Title 14: Aeronautics and Space
PART 171—NON-FEDERAL NAVIGATION FACILITIES
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Subpart J—Microwave Landing System (MLS)
Source: Docket No. 20669, 51 FR 33177, Sept. 18, 1986, unless otherwise noted.
§ 171.301 Scope.
This subpart sets forth minimum requirements for the approval, installation, operation and maintenance of non-Federal Microwave Landing System (MLS) facilities that provide the basis for instrument flight rules (IFR) and air traffic control procedures.
§ 171.303 Definitions.
As used in this subpart:
Auxiliary data means data transmitted in addition to basic data that provide ground equipment siting information for use in refining airborne position calculations and other supplementary information.
Basic data means data transmitted by the ground equipment that are associated directly with the operation of the landing guidance system.
Beam center means the midpoint between the –3 dB points on the leading and trailing edges of the scanning beam main lobe.
Beamwidth means the width of the scanning beam main lobe measured at the –3 dB points and defined in angular units on the boresight, in the horizontal plane for the azimuth function and in the vertical plane for the elevation function.
Clearance guidance sector means the volume of airspace, inside the coverage sector, within which the azimuth guidance information provided is not proportional to the angular displacement of the aircraft, but is a constant fly-left or fly-right indication of the direction relative to the approach course the aircraft should proceed in order to enter the proportional guidance sector.
Control Motion Noise (CMN) means those fluctuations in the guidance which affect aircraft attitude, control surface motion, column motion, and wheel motion. Control motion noise is evaluated by filtering the flight error record with a band-pass filter which has corner frequencies at 0.3 radian/sec and 10 radians/sec for azimuth data and 0.5 radian/sec and 10 radians/sec for elevation data.
Data rate means the average number of times per second that transmissions occur for a given function.
Differential Phase Shift Keying (DPSK) means differential phase modulation of the radio frequency carrier with relative phase states of 0 degree or 180 degrees.
Failure means the inability of an item to perform within previously specified limits.
Guard time means an unused period of time provided in the transmitted signal format to allow for equipment tolerances.
Integrity means that quality which relates to the trust which can be placed in the correctness of the information supplied by the facility.
Mean corrective time means the average time required to correct an equipment failure over a given period, after a service technician reaches the facility.
Mean course error means the mean value of the azimuth error along a specified radial of the azimuth function.
Mean glide path error means the mean value of the elevation error along a specified glidepath of the elevation function.
Mean-time-between-failures (MTBF) means the average time between equipment failures over a given period.
Microwave Landing System (MLS) means the MLS selected by ICAO for international standardization.
Minimum glidepath means the lowest angle of descent along the zero degree azimuth that is consistent with published approach procedures and obstacle clearance criteria.
MLS Approach Reference Datum is a point at a specified height located vertically above the intersection of the runway centerline and the threshold.
MLS back azimuth reference datum means a point 15 meters (50 feet) above the runway centerline at the runway midpoint.
MLS datum point means a point defined by the intersection of the runway centerline with a vertical plane perpendicular to the centerline and passing through the elevation antenna phase center.
Out of coverage indication (OCI) means a signal radiated into areas outside the intended coverage sector, where required, to specifically prevent invalid removal of an airborne warning indication in the presence of misleading guidance information.
Path Following Error (PFE) means the guidance perturbations which could cause aircraft displacement from the desired course or glidepath. It is composed of the path following noise and of the mean course error in the case of azimuth functions, or the mean glidepath error in the case of elevation functions. Path following errors are evaluated by filtering the flight error record with a second order low pass filter which has a corner frequency at 0.5 radian/sec for azimuth data or 1.5 radians/sec for elevation data.
Path following noise (PFN) means that portion of the guidance signal error which could cause displacement from the actual mean course line or mean glidepath as appropriate.
Split-site ground station means the type of ground station in which the azimuth portion of the ground station is located near the stop end of the runway, and the elevation portion is located near the approach end.
Time division multiplex (TDM) means that each function is transmitted on the same frequency in time sequence, with a distinct preamble preceding each function transmission.
§ 171.305 Requests for IFR procedure.
(a) Each person who requests an IFR procedure based on an MLS facility which that person owns must submit the following information with that request:
(1) A description of the facility and evidence that the equipment meets the performance requirements of §§171.309, 171.311, 171.313, 171.315, 171.317, 171.319, and 171.321 and is fabricated and installed in accordance with §171.323.
(2) A proposed procedure for operating the facility.
(3) A proposed maintenance organization and a maintenance manual that meets the requirements of §171.325.
(4) A statement of intent to meet the requirements of this subpart.
(5) A showing that the facility has an acceptable level of operational reliability and an acceptable standard of performance. Previous equivalent operational experience with a facility with identical design and operational characteristics will be considered in showing compliance with this subparagraph.
(b) FAA inspects and evaluates the MLS facility; it advises the owner of the results, and of any required changes in the MLS facility or in the maintenance manual or maintenance organization. The owner must then correct the deficiencies, if any, and operate the MLS facility for an in-service evaluation by the FAA.
§ 171.307 Minimum requirements for approval.
(a) The following are the minimum requirements that must be met before the FAA approves an IFR procedure for a non-Federal MLS facility:
(1) The performance of the MLS facility, as determined by flight and ground inspection conducted by the FAA, must meet the requirements of §§171.309, 171.311, 171.313, 171.315, 171.317, 171.319, and 171.321.
(2) The fabrication and installation of the equipment must meet the requirements of §171.323.
(3) The owner must agree to operate and maintain the MLS facility in accordance with §171.325.
(4) The owner must agree to furnish operational records as set forth in §171.327 and agree to allow the FAA to inspect the facility and its operation whenever necessary.
(5) The owner must assure the FAA that he will not withdraw the MLS facility from service without the permission of the FAA.
(6) The owner must bear all costs of meeting the requirements of this section and of any flight or ground inspection made before the MLS facility is commissioned.
(b) [Reserved]
§ 171.309 General requirements.
The MLS is a precision approach and landing guidance system which provides position information and various ground-to-air data. The position information is provided in a wide coverage sector and is determined by an azimuth angle measurement, an elevation angle measurement and a range (distance) measurement.
(a) An MLS constructed to meet the requirements of this subpart must include:
(1) Approach azimuth equipment, associated monitor, remote control and indicator equipment.
(2) Approach elevation equipment, associated monitor, remote control and indicator equipment.
(3) A means for the encoding and transmission of essential data words, associated monitor, remote control and indicator equipment. Essential data are basic data words 1, 2, 3, 4, and 6 and auxiliary data words A1, A2 and A3.
(4) Distance measuring equipment (DME), associated monitor, remote control and indicator equipment.
(5) Remote controls for paragraphs (a) (1), (2), (3), and (4) of this section must include as a minimum on/off and reset capabilities and may be integrated in the same equipment.
(6) At locations where a VHF marker beacon (75 MHz) is already installed, it may be used in lieu of the DME equipment.
(b) In addition to the equipment required in paragraph (a) of this section the MLS may include:
(1) Back azimuth equipment, associated monitor, remote control and indicator equipment. When Back Azimuth is provided, a means for transmission of Basic Data Word 5 and Auxiliary Data Word A4 shall also be provided.
(2) A wider proportional guidance sector which exceeds the minimum specified in §§171.313 and 171.317.
(3) Precision DME, associated monitor, remote control and indicator equipment.
(4) VHF marker beacon (75 MHz), associated monitor, remote control and indicator equipment.
(5) The MLS signal format will accommodate additional functions (e.g., flare elevation) which may be included as desired. Remote controls for paragraphs (b) (1), (3) and (4) of this section must include as a minimum on/off and reset capabilities, and may be integrated in the same equipment.
(6) Provisions for the encoding and transmission of additional auxiliary data words, associated monitor, remote control and indicator equipment.
(c) MLS ground equipment must be designed to operate on a nominal 120/240 volt, 60 Hz, 3-wire single phase AC power source and must meet the following service conditions:
(1) AC line parameters, DC voltage, elevation and duty:
120 VAC nominal value—102 V to 138 V (±1 V)*
240 VAC nominal value—204 V to 276 V (±2 V)*
60 Hz AC line frequency—57 Hz to 63 Hz (±0.2 Hz)*
*Note: Where discrete values of the above frequency or voltages are specified for testing purposes, the tolerances given in parentheses indicated by an asterisk apply to the test instruments used to measure these parameters.
Elevation—0 to 3000 meters (10,000 feet) above sea level
Duty—Continuous, unattended
(2) Ambient conditions within the shelter for electronic equipment installed in shelters are:
Temperature, −10 °C to +50 °C
Relative humidity, 5% to 90%
(3) Ambient conditions for electronic equipment and all other equipment installed outdoors (for example, antenna, field detectors, and shelters):
Temperature, −50 °C to +70 °C
Relative humidity, 5% to 100%
(4) All equipment installed outdoors must operate satisfactorily under the following conditions:
Wind Velocity: The ground equipment shall remain within monitor limits with wind velocities of up to 70 knots from such directions that the velocity component perpendicular to runway centerline does not exceed 35 knots. The ground equipment shall withstand winds up to 100 knots from any direction without damage.
Hail Stones: 1.25 centimeters (1/2 inch) diameter.
Rain: Provide required coverage with rain falling at a rate of 50 millimeters (2 inches) per hour, through a distance of 9 kilometers (5 nautical miles) and with rain falling at the rate of 25 millimeters (1 inch) per hour for the additional 28 kilometers (15 nautical miles).
Ice Loading: Encased in 1.25 centimeters (1/2 inch) radial thickness of clear ice.
Antenna Radome De-Icing: Down to −6°C (20 °F) and wind up to 35 knots.
(d) The transmitter frequencies of an MLS must be in accordance with the frequency plan approved by the FAA.
(e) The DME component listed in paragraph (a)(4) of this section must comply with the minimum standard performance requirements specified in subpart G of this part.
(f) The marker beacon components listed in paragraph (b)(4) of this section must comply with the minimum standard performance requirements specified in subpart H of this part.
§ 171.311 Signal format requirements.
The signals radiated by the MLS must conform to the signal format in which angle guidance functions and data functions are transmitted sequentially on the same C-band frequency. Each function is identified by a unique digital code which initializes the airborne receiver for proper processing. The signal format must meet the following minimum requirements:
(a) Frequency assignment. The ground components (except DME/Marker Beacon) must operate on a single frequency assignment or channel, using time division multiplexing. These components must be capable of operating on any one of the 200 channels spaced 300 KHz apart with center frequencies from 5031.0 MHz to 5090.7 MHz and with channel numbering as shown in Table 1a. The operating radio frequencies of all ground components must not vary by more than ±10 KHz from the assigned frequency. Any one transmitter frequency must not vary more than ±50 Hz in any one second period. The MLS angle/data and DME equipment must operate on one of the paired channels as shown in Table 1b.
Table 1a_Frequency Channel Plan------------------------------------------------------------------------ Frequency Channel No. (MHz)------------------------------------------------------------------------500.......................................................... 5031.0501.......................................................... 5031.3502.......................................................... 5031.6503.......................................................... 5031.9504.......................................................... 5032.2505.......................................................... 5032.5506.......................................................... 5032.8507.......................................................... 5033.1508.......................................................... 5033.4509.......................................................... 5033.7510.......................................................... 5034.0511.......................................................... 5034.3 * * * * *598.......................................................... 5060.4599.......................................................... 5060.7600.......................................................... 5061.0601.......................................................... 5061.3 * * * * *698.......................................................... 5090.4699.......................................................... 5090.7------------------------------------------------------------------------
Table 1b_Channels-------------------------------------------------------------------------------------------------------------------------------------------------------- Channel pairing DME parameters-------------------------------------------------------------------------------------------------------------------------------------------------------- Interrogation Reply ----------------------------------------------------------- MLS Pulse codes VHF angle MLS Ch. ------------------------------ DME No. freq. freq. No. Freq. DME/P Mode Freq. Pulse MHz MHz MHz DME/N -------------------- MHz codes µs IA FA µs µs µs--------------------------------------------------------------------------------------------------------------------------------------------------------* 1X.......................................................... ........ ........ ........ 1025 12 ........ ........ 962 12** 1Y......................................................... ........ ........ ........ 1025 36 ........ ........ 1088 30* 2X.......................................................... ........ ........ ........ 1026 12 ........ ........ 963 12** 2Y......................................................... ........ ........ ........ 1026 36 ........ ........ 1089 30* 3X.......................................................... ........ ........ ........ 1027 12 ........ ........ 964 12** 3Y......................................................... ........ ........ ........ 1027 36 ........ ........ 1090 30* 4X.......................................................... ........ ........ ........ 1028 12 ........ ........ 965 12** 4Y......................................................... ........ ........ ........ 1028 36 ........ ........ 1091 30* 5X.......................................................... ........ ........ ........ 1029 12 ........ ........ 966 12** 5Y......................................................... ........ ........ ........ 1029 36 ........ ........ 1092 30* 6X.......................................................... ........ ........ ........ 1030 12 ........ ........ 967 12** 6Y......................................................... ........ ........ ........ 1030 36 ........ ........ 1093 30* 7X.......................................................... ........ ........ ........ 1031 12 ........ ........ 968 12** 7Y......................................................... ........ ........ ........ 1031 36 ........ ........ 1094 30* 8X.......................................................... ........ ........ ........ 1032 12 ........ ........ 969 12** 8Y......................................................... ........ ........ ........ 1032 36 ........ ........ 1095 30* 9X.......................................................... ........ ........ ........ 1033 12 ........ ........ 970 12** 9Y......................................................... ........ ........ ........ 1033 36 ........ ........ 1096 30* 10X......................................................... ........ ........ ........ 1034 12 ........ ........ 971 12** 10Y........................................................ ........ ........ ........ 1034 36 ........ ........ 1097 30* 11X......................................................... ........ ........ ........ 1035 12 ........ ........ 972 12** 11Y........................................................ ........ ........ ........ 1035 36 ........ ........ 1098 30* 12X......................................................... ........ ........ ........ 1036 12 ........ ........ 973 12** 12Y........................................................ ........ ........ ........ 1036 36 ........ ........ 1099 30* 13X......................................................... ........ ........ ........ 1037 12 ........ ........ 974 12** 13Y........................................................ ........ ........ ........ 1037 36 ........ ........ 1100 30* 14X......................................................... ........ ........ ........ 1038 12 ........ ........ 975 12** 14Y........................................................ ........ ........ ........ 1038 36 ........ ........ 1101 30* 15X......................................................... ........ ........ ........ 1039 12 ........ ........ 976 12** 15Y........................................................ ........ ........ ........ 1039 36 ........ ........ 1102 30* 16X......................................................... ........ ........ ........ 1040 12 ........ ........ 977 12** 16Y........................................................ ........ ........ ........ 1040 36 ........ ........ 1103 30Δ17X.................................................... 108.00 ........ ........ 1041 12 ........ ........ 978 1217Y........................................................... 108.05 5043.0 540 1041 36 36 42 1104 3017Z........................................................... ........ 5043.3 541 1041 ........ 21 27 1104 1518X........................................................... 108.10 5031.0 500 1042 12 12 18 979 1218W........................................................... ........ 5031.3 501 1042 ........ 24 30 979 2418Y........................................................... 108.15 5043.6 542 1042 36 36 42 1105 3018Z........................................................... ........ 5043.9 543 1042 ........ 21 27 1105 1519X........................................................... 108.20 ........ ........ 1043 12 ........ ........ 980 1219Y........................................................... 108.25 5044.2 544 1043 36 36 42 1106 3019Z........................................................... ........ 5044.5 545 1043 ........ 21 27 1106 1520X........................................................... 108.30 5031.6 502 1044 12 12 18 981 1220W........................................................... ........ 5031.9 503 1044 ........ 24 30 981 2420Y........................................................... 108.35 5044.8 546 1044 36 36 42 1107 3020Z........................................................... ........ 5045.1 547 1044 ........ 21 27 1107 1521X........................................................... 108.40 ........ ........ 1045 12 ........ ........ 982 1221Y........................................................... 108.45 5045.4 548 1045 36 36 42 1108 3021Z........................................................... ........ 5045.7 549 1045 ........ 21 27 1108 1522X........................................................... 108.50 5032.2 504 1046 12 12 18 983 1222W........................................................... ........ 5032.5 505 1046 ........ 24 30 983 2422Y........................................................... 108.55 5046.0 550 1046 36 36 42 1109 3022Z........................................................... ........ 5046.3 551 1046 ........ 21 27 1109 1523X........................................................... 108.60 ........ ........ 1047 12 ........ ........ 984 1223Y........................................................... 108.65 5046.6 552 1047 36 36 42 1110 3023Z........................................................... ........ 5046.9 553 1047 ........ 21 27 1110 1524X........................................................... 108.70 5032.8 506 1048 12 12 18 985 1224W........................................................... ........ 5033.1 507 1048 ........ 24 30 985 2424Y........................................................... 108.75 5047.2 554 1048 36 36 42 1111 3024Z........................................................... ........ 5047.5 555 1048 ........ 21 27 1111 1525X........................................................... 108.80 ........ ........ 1049 12 ........ ........ 986 1225Y........................................................... 108.85 5047.8 556 1049 36 36 42 1112 3025Z........................................................... ........ 5048.1 557 1049 ........ 21 27 1112 1526X........................................................... 108.90 5033.4 508 1050 12 12 18 987 1226W........................................................... ........ 5033.7 509 1050 ........ 24 30 987 2426Y........................................................... 108.95 5048.4 558 1050 36 36 42 1113 3026Z........................................................... ........ 5048.7 559 1050 ........ 21 27 1113 1527X........................................................... 109.00 ........ ........ 1051 12 ........ ........ 988 1227Y........................................................... 109.05 5049.0 560 1051 36 36 42 1114 3027Z........................................................... ........ 5049.3 561 1051 ........ 21 27 1114 1528X........................................................... 109.10 5034.0 510 1052 12 12 18 989 1228W........................................................... ........ 5034.3 511 1052 ........ 24 30 989 2428Y........................................................... 109.15 5049.6 562 1052 36 36 42 1115 3028Z........................................................... ........ 5049.9 563 1052 ........ 21 27 1115 1529X........................................................... 109.20 ........ ........ 1053 12 ........ ........ 990 1229Y........................................................... 109.25 5050.2 564 1053 36 36 42 1116 3029Z........................................................... ........ 5050.5 565 1043 ........ 21 27 1116 1530X........................................................... 109.30 5034.6 512 1054 12 12 18 991 1230W........................................................... ........ 5034.9 513 1054 ........ 24 30 991 2430Y........................................................... 109.35 5050.8 566 1054 36 36 42 1117 3030Z........................................................... ........ 5051.1 567 1054 ........ 21 27 1117 1531X........................................................... 109.40 ........ ........ 1055 12 ........ ........ 992 1231Y........................................................... 109.45 5051.4 568 1055 36 36 42 1118 3031Z........................................................... ........ 5051.7 569 1055 ........ 21 27 1118 1532X........................................................... 109.50 5035.2 514 1056 12 12 18 993 1232W........................................................... ........ 5035.5 515 1056 ........ 24 30 993 2432Y........................................................... 109.55 5052.0 570 1056 36 36 42 1119 3032Z........................................................... ........ 5052.3 571 1056 ........ 21 27 1119 1533X........................................................... 109.60 ........ ........ 1057 12 ........ ........ 994 1233Y........................................................... 109.65 5052.6 572 1057 36 36 42 1120 3033Z........................................................... ........ 5052.9 573 1057 ........ 21 27 1120 1534X........................................................... 109.70 5035.8 516 1058 12 12 18 995 1234W........................................................... ........ 5036.1 517 1058 ........ 24 30 995 2434Y........................................................... 109.75 5053.2 574 1058 36 36 42 1121 3034Z........................................................... ........ 5053.5 575 1058 ........ 21 27 1121 1535X........................................................... 109.80 ........ ........ 1059 12 ........ ........ 996 1235Y........................................................... 109.85 5053.8 576 1059 36 36 42 1122 3035Z........................................................... ........ 5054.1 577 1059 ........ 21 27 1122 1536X........................................................... 109.90 5036.4 518 1060 12 12 18 997 1236W........................................................... ........ 5036.7 519 1060 ........ 24 30 997 2436Y........................................................... 109.95 5054.4 578 1060 36 36 42 1123 3036Z........................................................... ........ 5054.7 579 1060 ........ 21 27 1123 1537X........................................................... 110.00 ........ ........ 1061 12 ........ ........ 998 1237Y........................................................... 110.05 5055.0 580 1061 36 36 42 1124 3037Z........................................................... ........ 5055.3 581 1061 ........ 21 27 1124 1538X........................................................... 110.10 5037.0 520 1062 12 12 18 999 1238W........................................................... ........ 5037.3 521 1062 ........ 24 30 999 2438Y........................................................... 110.15 5055.6 582 1062 36 36 42 1125 3038Z........................................................... ........ 5055.9 583 1062 ........ 21 27 1125 1539X........................................................... 110.20 ........ ........ 1063 12 ........ ........ 1000 1239Y........................................................... 110.25 5056.2 584 1063 36 36 42 1126 3039Z........................................................... ........ 5056.5 585 1063 ........ 21 27 1126 1540X........................................................... 110.30 5037.6 522 1064 12 12 18 1001 1240W........................................................... ........ 5037.9 523 1064 ........ 24 30 1001 2440Y........................................................... 110.35 5056.8 586 1064 36 36 42 1127 3040Z........................................................... ........ 5057.1 587 1064 ........ 21 27 1127 1541X........................................................... 110.40 ........ ........ 1065 12 ........ ........ 1002 1241Y........................................................... 110.45 5057.4 588 1065 36 36 42 1128 3041Z........................................................... ........ 5057.7 589 1065 ........ 21 27 1128 1542X........................................................... 110.50 5038.2 524 1066 12 12 18 1003 1242W........................................................... ........ 5038.5 525 1066 ........ 24 30 1003 2442Y........................................................... 110.55 5058.0 590 1066 36 36 42 1129 3042Z........................................................... ........ 5058.3 591 1066 ........ 21 27 1129 1543X........................................................... 110.60 ........ ........ 1067 12 ........ ........ 1004 1243Y........................................................... 110.65 5058.6 592 1067 36 36 42 1130 3043Z........................................................... ........ 5058.9 593 1067 ........ 21 27 1130 1544X........................................................... 110.70 5038.8 526 1068 12 12 18 1005 1244W........................................................... ........ 5039.1 527 1068 ........ 24 30 1005 2444Y........................................................... 110.75 5059.2 594 1068 36 36 42 1131 3044Z........................................................... ........ 5059.5 595 1068 ........ 21 27 1131 1545X........................................................... 110.80 ........ ........ 1069 12 ........ ........ 1006 1245Y........................................................... 110.85 5059.8 596 1069 36 36 42 1132 3045Z........................................................... ........ 5060.1 597 1069 ........ 21 27 1132 1546X........................................................... 110.90 5039.4 528 1070 12 12 18 1007 1246W........................................................... ........ 5039.7 529 1070 ........ 24 30 1007 2446Y........................................................... 110.95 5060.4 598 1070 36 36 42 1133 3046Z........................................................... ........ 5060.7 599 1070 ........ 21 27 1133 1547X........................................................... 111.00 ........ ........ 1071 12 ........ ........ 1008 1247Y........................................................... 111.05 5061.0 600 1071 36 36 42 1134 3047Z........................................................... ........ 5061.3 601 1071 ........ 21 27 1134 1548X........................................................... 111.10 5040.0 530 1072 12 12 18 1009 1248W........................................................... ........ 5040.3 531 1072 ........ 24 30 1009 2448Y........................................................... 111.15 5061.6 602 1072 36 36 42 1135 3048Z........................................................... ........ 5061.9 603 1072 ........ 21 27 1135 1549X........................................................... 111.20 ........ ........ 1073 12 ........ ........ 1010 1249Y........................................................... 111.25 5062.2 604 1073 36 36 42 1136 3049Z........................................................... ........ 5062.5 605 1073 ........ 21 27 1136 1550X........................................................... 111.30 5040.6 532 1074 12 12 18 1011 1250W........................................................... ........ 5040.9 533 1074 ........ 24 30 1011 2450Y........................................................... 111.35 5062.8 606 1074 36 36 42 1137 3050Z........................................................... ........ 5063.1 607 1074 ........ 21 27 1137 1551X........................................................... 111.40 ........ ........ 1075 12 ........ ........ 1012 1251Y........................................................... 111.45 5063.4 608 1075 36 36 42 1138 3051Z........................................................... ........ 5063.7 609 1075 ........ 21 27 1138 1552X........................................................... 111.50 5041.2 534 1076 12 12 18 1013 1252W........................................................... ........ 5041.5 535 1076 ........ 24 30 1013 2452Y........................................................... 111.55 5064.0 610 1076 36 36 42 1139 3052Z........................................................... ........ 5064.3 611 1076 ........ 21 27 1139 1553X........................................................... 111.60 ........ ........ 1077 12 ........ ........ 1014 1253Y........................................................... 111.65 5064.6 612 1077 36 36 42 1140 3053Z........................................................... ........ 5064.9 613 1077 ........ 21 27 1140 1554X........................................................... 111.70 5041.8 536 1078 12 12 18 1015 1254W........................................................... ........ 5042.1 537 1078 ........ 24 30 1015 2454Y........................................................... 111.75 5065.2 614 1078 36 36 42 1141 3054Z........................................................... ........ 5065.5 615 1078 ........ 21 27 1141 1555X........................................................... 111.80 ........ ........ 1079 12 ........ ........ 1016 1255Y........................................................... 111.85 5065.8 616 1079 36 36 42 1142 3055Z........................................................... ........ 5066.1 617 1079 ........ 21 27 1142 1556X........................................................... 111.90 5042.4 538 1080 12 12 18 1017 1256W........................................................... ........ 5042.7 539 1080 ........ 24 30 1017 2456Y........................................................... 111.95 5066.4 618 1080 36 36 42 1143 3056Z........................................................... ........ 5066.7 619 1080 ........ 21 27 1143 1557X........................................................... 112.00 ........ ........ 1081 12 ........ ........ 1018 1257Y........................................................... 112.05 ........ ........ 1081 36 ........ ........ 1144 3058X........................................................... 112.10 ........ ........ 1082 12 ........ ........ 1019 1258Y........................................................... 112.15 ........ ........ 1082 36 ........ ........ 1145 3059X........................................................... 112.20 ........ ........ 1083 12 ........ ........ 1020 1259Y........................................................... 122.25 ........ ........ 1083 36 ........ ........ 1146 30** 60X........................................................ ........ ........ ........ 1084 12 ........ ........ 1021 12** 60Y........................................................ ........ ........ ........ 1084 36 ........ ........ 1147 30** 61X........................................................ ........ ........ ........ 1085 12 ........ ........ 1022 12** 61Y........................................................ ........ ........ ........ 1085 36 ........ ........ 1148 30** 62X........................................................ ........ ........ ........ 1086 12 ........ ........ 1023 12** 62Y........................................................ ........ ........ ........ 1086 36 ........ ........ 1149 30** 63X........................................................ ........ ........ ........ 1037 12 ........ ........ 1024 12** 63Y........................................................ ........ ........ ........ 1087 36 ........ ........ 1150 30** 64X........................................................ ........ ........ ........ 1088 12 ........ ........ 1151 12** 64Y........................................................ ........ ........ ........ 1088 36 ........ ........ 1025 30** 65X........................................................ ........ ........ ........ 1089 12 ........ ........ 1152 12** 65Y........................................................ ........ ........ ........ 1089 36 ........ ........ 1026 30** 66X........................................................ ........ ........ ........ 1090 12 ........ ........ 1153 12** 66Y........................................................ ........ ........ ........ 1090 36 ........ ........ 1027 30** 67X........................................................ ........ ........ ........ 1091 12 ........ ........ 1154 12** 67Y........................................................ ........ ........ ........ 1091 36 ........ ........ 1028 30** 68X........................................................ ........ ........ ........ 1092 12 ........ ........ 1155 12** 68Y........................................................ ........ ........ ........ 1092 36 ........ ........ 1029 30** 69X........................................................ ........ ........ ........ 1093 12 ........ ........ 1156 12** 69Y........................................................ ........ ........ ........ 1093 36 ........ ........ 1030 3070X........................................................... 112.30 ........ ........ 1094 12 ........ ........ 1157 12** 70Y........................................................ 112.35 ........ ........ 1094 36 ........ ........ 1031 3071X........................................................... 112.40 ........ ........ 1095 12 ........ ........ 1158 12** 71Y........................................................ 112.45 ........ ........ 1095 36 ........ ........ 1032 3072X........................................................... 112.50 ........ ........ 1096 12 ........ ........ 1159 12** 72Y........................................................ 112.55 ........ ........ 1096 36 ........ ........ 1033 3073X........................................................... 112.60 ........ ........ 1097 12 ........ ........ 1160 12** 73Y........................................................ 112.65 ........ ........ 1097 36 ........ ........ 1034 3074X........................................................... 112.70 ........ ........ 1098 12 ........ ........ 1161 12** 74Y........................................................ 112.75 ........ ........ 1098 36 ........ ........ 1035 3075X........................................................... 112.80 ........ ........ 1099 12 ........ ........ 1162 12** 75Y........................................................ 112.85 ........ ........ 1099 36 ........ ........ 1036 3076X........................................................... 112.90 ........ ........ 1100 12 ........ ........ 1163 12** 76Y........................................................ 112.95 ........ ........ 1100 36 ........ ........ 1037 3077X........................................................... 113.00 ........ ........ 1101 12 ........ ........ 1164 12** 77Y........................................................ 113.05 ........ ........ 1101 36 ........ ........ 1038 3078X........................................................... 113.10 ........ ........ 1102 12 ........ ........ 1165 12** 78Y........................................................ 113.15 ........ ........ 1102 36 ........ ........ 1039 3079X........................................................... 113.20 ........ ........ 1103 12 ........ ........ 1166 12** 79Y........................................................ 113.25 ........ ........ 1103 36 ........ ........ 1040 3080X........................................................... 113.30 ........ ........ 1104 12 ........ ........ 1167 1280Y........................................................... 113.35 5067.0 620 1104 36 36 42 1041 3080Z........................................................... ........ 5067.3 621 1104 ........ 21 27 1041 1581X........................................................... 113.40 ........ ........ 1105 12 ........ ........ 1168 1281Y........................................................... 113.45 5067.6 622 1105 36 36 42 1042 3081Z........................................................... ........ 5067.9 623 1005 ........ 21 27 1042 1582X........................................................... 113.50 ........ ........ 1106 12 ........ ........ 1169 1282Y........................................................... 113.55 5068.2 624 1106 36 36 42 1043 3082Z........................................................... ........ 5068.5 625 1106 ........ 21 27 1043 1583X........................................................... 113.60 ........ ........ 1107 12 ........ ........ 1170 1283Y........................................................... 113.65 5068.8 626 1107 36 36 42 1044 3083Z........................................................... ........ 5069.1 627 1107 ........ 21 27 1044 1584X........................................................... 113.70 ........ ........ 1108 12 ........ ........ 1171 1284Y........................................................... 113.75 5069.4 628 1108 36 36 42 1045 3084Z........................................................... ........ 6069.7 629 1108 ........ 21 27 1045 1585X........................................................... 113.80 ........ ........ 1109 12 ........ ........ 1172 1285Y........................................................... 113.85 5070.0 630 1109 36 36 42 1046 3085Z........................................................... ........ 5070.3 631 1109 ........ 21 27 1046 1586X........................................................... 113.90 ........ ........ 1110 12 ........ ........ 1173 1286Y........................................................... 113.95 5070.6 632 1110 36 36 42 1047 3086Z........................................................... ........ 5070.9 633 1110 ........ 21 27 1047 1587X........................................................... 114.00 ........ ........ 1111 12 ........ ........ 1174 1287Y........................................................... 114.05 5071.2 634 1111 36 36 42 1048 3087Z........................................................... ........ 5071.5 635 1111 ........ 21 27 1048 1588X........................................................... 114.10 ........ ........ 1112 12 ........ ........ 1175 1288Y........................................................... 114.15 5071.8 636 1112 36 36 42 1049 3088Z........................................................... ........ 5072.1 637 1112 ........ 21 27 1049 1589X........................................................... 114.20 ........ ........ 1113 12 ........ ........ 1176 1289Y........................................................... 114.25 5072.4 638 1113 36 36 42 1050 3089Z........................................................... ........ 5072.7 639 1113 ........ 21 27 1050 1590X........................................................... 114.30 ........ ........ 1114 12 ........ ........ 1177 1290Y........................................................... 114.35 5073.0 640 1114 36 36 42 1051 3090Z........................................................... ........ 5073.3 641 1114 ........ 21 27 1051 1591X........................................................... 114.40 ........ ........ 1115 12 ........ ........ 1178 1291Y........................................................... 114.45 5073.6 642 1115 36 36 42 1052 3091Z........................................................... ........ 5073.9 643 1115 ........ 21 27 1052 1592X........................................................... 114.50 ........ ........ 1116 12 ........ ........ 1179 1292Y........................................................... 114.55 5074.2 644 1116 36 36 42 1053 3092Z........................................................... ........ 5074.5 645 1116 ........ 21 27 1053 1593X........................................................... 114.60 ........ ........ 1117 12 ........ ........ 1180 1293Y........................................................... 114.65 5074.8 646 1117 36 36 42 1054 3093Z........................................................... ........ 5075.1 647 1117 ........ 21 27 1054 1594X........................................................... 114.70 ........ ........ 1118 12 ........ ........ 1181 1294Y........................................................... 114.75 5075.4 648 1118 36 36 42 1055 3094Z........................................................... ........ 5075.7 649 1118 ........ 21 27 1055 1595X........................................................... 114.80 ........ ........ 1119 12 ........ ........ 1182 1295Y........................................................... 114.85 5076.0 650 1119 36 36 42 1056 3095Z........................................................... ........ 5076.3 651 1119 ........ 21 27 1056 1596X........................................................... 114.90 ........ ........ 1120 12 ........ ........ 1183 1296Y........................................................... 114.95 5076.6 652 1120 36 36 42 1057 3096Z........................................................... ........ 5076.9 653 1120 ........ 21 27 1057 1597X........................................................... 115.00 ........ ........ 1121 12 ........ ........ 1184 1297Y........................................................... 115.05 5077.2 654 1121 36 36 42 1058 3097Z........................................................... ........ 5077.5 655 1121 ........ 21 27 1058 1598X........................................................... 115.10 ........ ........ 1122 12 ........ ........ 1185 1298Y........................................................... 115.15 5077.8 656 1122 36 36 42 1059 3098Z........................................................... ........ 5078.1 657 1122 ........ 21 27 1059 1599X........................................................... 115.20 ........ ........ 1123 12 ........ ........ 1186 1299Y........................................................... 115.25 5078.4 658 1123 36 36 42 1060 3099Z........................................................... ........ 5078.7 659 1123 ........ 21 27 1060 15100X.......................................................... 115.30 ........ ........ 1124 12 ........ ........ 1187 12100Y.......................................................... 115.35 5079.0 660 1124 36 36 42 1061 30100Z.......................................................... ........ 5079.3 661 1124 ........ 21 27 1061 15101X.......................................................... 115.40 ........ ........ 1125 12 ........ ........ 1188 12101Y.......................................................... 115.45 5079.6 662 1125 36 36 42 1062 30101Z.......................................................... ........ 5079.9 663 1125 ........ 21 27 1062 15102X.......................................................... 115.50 ........ ........ 1126 12 ........ ........ 1189 12102Y.......................................................... 115.55 5080.2 664 1126 36 36 42 1063 30102Z.......................................................... ........ 5080.5 665 1126 ........ 21 27 1063 15103X.......................................................... 115.60 ........ ........ 1127 12 ........ ........ 1190 12103Y.......................................................... 115.65 5080.B 666 1127 36 36 42 1064 30103Z.......................................................... ........ 5081.1 667 1127 ........ 21 27 1064 19104X.......................................................... 115.70 ........ ........ 1128 12 ........ ........ 1191 12104Y.......................................................... 115.75 5081.4 668 1128 36 36 42 1065 30104Z.......................................................... ........ 5081.7 669 1128 ........ 21 27 1065 19105X.......................................................... 115.80 ........ ........ 1129 12 ........ ........ 1192 12105Y.......................................................... 115.85 5082.0 670 1129 36 36 42 1066 30105Z.......................................................... ........ 5082.3 671 1129 ........ 21 27 1066 15106X.......................................................... 115.90 ........ ........ 1130 12 ........ ........ 1193 12106Y.......................................................... 115.95 5082.6 672 1130 36 36 42 1067 30106Z.......................................................... ........ 5082.9 673 1130 ........ 21 27 1067 15107X.......................................................... 116.00 ........ ........ 1131 12 ........ ........ 1194 12107Y.......................................................... 116.05 5083.2 674 1131 36 36 42 1068 30107Z.......................................................... ........ 5083.5 675 1131 ........ 21 27 1068 15108X.......................................................... 116.10 508 ........ 1132 12 ........ ........ 1195 12108Y.......................................................... 116.15 5083.8 676 1132 36 36 42 1069 30108Z.......................................................... ........ 5084.1 677 1132 ........ 21 27 1069 15109X.......................................................... 116.20 ........ ........ 1133 12 ........ ........ 1196 12109Y.......................................................... 116.25 5084.4 678 1133 36 36 42 1070 30109Z.......................................................... ........ 5084.7 679 1133 ........ 21 27 1070 15110X.......................................................... 116.30 ........ ........ 1134 12 ........ ........ 1197 12110Y.......................................................... 116.35 5085.0 680 1134 36 36 42 1071 30110Z.......................................................... ........ 5085.3 681 1134 ........ 21 27 1071 15111X.......................................................... 116.40 ........ ........ 1135 12 ........ ........ 1198 12111Y.......................................................... 116.45 5086.6 682 1135 36 36 42 1072 30111Z.......................................................... ........ 5085.9 683 1135 ........ 21 27 1072 15112X.......................................................... 116.50 ........ ........ 1136 12 ........ ........ 1199 12112Y.......................................................... 116.55 5086.2 684 1136 36 36 42 1073 30112Z.......................................................... ........ 5086.5 685 1136 ........ 21 27 1073 15113X.......................................................... 116.60 ........ ........ 1137 12 ........ ........ 1200 12113Y.......................................................... 116.65 5086.8 686 1137 36 36 42 1074 30113Z.......................................................... ........ 5087.1 687 1137 ........ 21 27 1074 15114X.......................................................... 116.70 ........ ........ 1138 12 ........ ........ 1201 12114Y.......................................................... 116.75 5087.4 688 1138 36 36 42 1075 30114Z.......................................................... ........ 5087.7 689 1138 ........ 21 27 1075 15115X.......................................................... 116.80 ........ ........ 1139 12 ........ ........ 1202 12115Y.......................................................... 116.85 5088.0 690 1139 36 36 42 1076 30115Z.......................................................... ........ 5088.3 691 1139 ........ 21 27 1076 15116X.......................................................... 116.90 ........ ........ 1140 12 ........ ........ 1203 12116Y.......................................................... 116.95 5088.6 692 1140 36 36 42 1077 30116Z.......................................................... ........ 5088.9 693 1140 ........ 21 27 1077 15117X.......................................................... 117.00 ........ ........ 1141 12 ........ ........ 1204 12117Y.......................................................... 117.05 5089.2 694 1141 36 36 42 1078 30117Z.......................................................... ........ 5089.5 695 1141 ........ 21 27 1078 15118X.......................................................... 117.10 ........ ........ 1142 12 ........ ........ 12.5 12118Y.......................................................... 117.15 5089.8 696 1142 36 36 42 1079 30118Z.......................................................... ........ 5090.1 697 1142 ........ 21 27 1079 12119X.......................................................... 117.20 ........ ........ 1143 12 ........ ........ 1206 12119Y.......................................................... 117.25 5090.4 698 1143 36 36 42 1080 30119Z.......................................................... ........ 5090.7 699 1143 ........ 21 27 1080 15120X.......................................................... 117.30 ........ ........ 1144 12 ........ ........ 1207 12120Y.......................................................... 117.35 ........ ........ 1144 36 ........ ........ 1081 30121X.......................................................... 117.40 ........ ........ 1145 12 ........ ........ 1208 12121Y.......................................................... 117.45 ........ ........ 1145 36 ........ ........ 1082 30122X.......................................................... 117.50 ........ ........ 1146 12 ........ ........ 1209 12122Y.......................................................... 117.55 ........ ........ 1146 36 ........ ........ 1083 30123X.......................................................... 117.60 ........ ........ 1147 12 ........ ........ 1210 12123Y.......................................................... 117.65 ........ ........ 1147 36 ........ ........ 1084 30124X.......................................................... 117.70 ........ ........ 1148 12 ........ ........ 1211 12** 124Y....................................................... 117.75 ........ ........ 1148 36 ........ ........ 1085 30125X.......................................................... 117.80 ........ ........ 1149 12 ........ ........ 1212 12** 125Y....................................................... 117.85 ........ ........ 1149 36 ........ ........ 1086 30126X.......................................................... 117.90 ........ ........ 1150 12 ........ ........ 1213 12** 126Y....................................................... 117.95 ........ ........ 1150 36 ........ ........ 1087 30--------------------------------------------------------------------------------------------------------------------------------------------------------Notes:* These channels are reserved exclusively for national allotments.** These channels may be used for national allotment on a secondary basis. The primary reason for reserving these channels is to provide protection for the secondary Surveillance Radar (SSR) system.Δ 108.0 MHz is not scheduled for assignment to ILS service. The associated DME operating channel No. 17X may be assigned to the emergency service.
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(b) Polarization. (1) The radio frequency emissions from all ground equipment must be nominally vertically polarized. Any horizontally polarized radio frequency emission component from the ground equipment must not have incorrectly coded angle information such that the limits specified in paragraphs (b) (2) and (3) of this section are exceeded.
(2) Rotation of the receiving antenna thirty degrees from the vertically polarized position must not cause the path following error to exceed the allowed error at that location.
(c) Modulation requirements. Each function transmitter must be capable of DPSK and continuous wave (CW) modulations of the RF carrier which have the following characteristics.
(1) DPSK. The DPSK signal must have the following characteristics:
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bit rate.................................. 15.625 KHzbit length................................ 64 microsecondslogic ``0''............................... no phase transitionlogic ``1''............................... phase transitionphase transition.......................... less than 10 microsecondsphase tolerance........................... ±10 degrees
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The phase shall advance (or retard) monotonically throughout the transition region. Amplitude modulation during the phase transition period shall not be used.
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(2) CW. The CW pulse transmissions and the CW angle transmissions as may be required in the signal format of any function must have characteristics such that the requirements of paragraph (d) of this section are met.
(d) Radio frequency signal spectrum. The transmitted signal must be such that during the transmission time, the mean power density above a height of 600 meters (2000 feet) does not exceed −100.5 dBW/m2 for angle guidance and −95.5 dBW/m2 for data, as measured in a 150 KHz bandwidth centered at a frequency of 840 KHz or more from the assigned frequency.
(e) Synchronization. Synchronization between the azimuth and elevation components is required and, in split-site configurations, would normally be accomplished by landline interconnections. Synchronization monitoring must be provided to preclude function overlap.
(f) Transmission rates. Angle guidance and data signals must be transmitted at the following average repetition rates:
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------------------------------------------------------------------------ Average Function data rate (Hertz)------------------------------------------------------------------------Approach Azimuth............................................. 13 ±0 .5High Rate Approach Azimuth................................... \1\ 39 ±1 .5Approach Elevation........................................... 39 ±1 .5Back Azimuth................................................. 6.5 ±0 .25Basic Data................................................... (\2\)Auxiliary Data............................................... (\3\)------------------------------------------------------------------------\1\ The higher rate is recommended for azimuth scanning antennas with beamwidths greater than two degrees. It should be noted that the time available in the signal format for additional functions is limited when the higher rate is used.\2\ Refer to Table 8a.\3\ Refer to Table 8c.
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(g) Transmission sequences. Sequences of angle transmissions which will generate the required repetition rates are shown in Figures 2 and 3.
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(h) TDM cycle. The time periods between angle transmission sequences must be varied so that exact repetitions do not occur within periods of less than 0.5 second in order to protect against synchronous interference. One such combination of sequences is shown in Figure 4 which forms a full multiplex cycle. Data may be transmitted during suitable open times within or between the sequences.
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(i) Function Formats (General). Each angle function must contain the following elements: a preamble; sector signals; and a TO and FRO angle scan organized as shown in Figure 5a. Each data function must contain a preamble and a data transmission period organized as shown in Figure 5b.
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(1) Preamble format. The transmitted angle and date functions must use the preamble format shown in Figure 6. This format consists of a carrier acquisition period of unmodulated CW transmission followed by a receiver synchronization code and a function identification code. The preamble timing must be in accordance with Table 2.
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(i) Digital codes. The coding used in the preamble for receiver synchronization is a Barker code logic 11101. The time of the last phase transition midpoint in the code shall be the receiver reference time (see Table 2). The function identification codes must be as shown in Table 3. The last two bits (I11 and I12) of the code are parity bits obeying the equations:
I6+I7+I8+I9+I10+I11=Even
I6+I8+I10+I12=Even
(ii) Data modulation. The digital code portions of the preamble must be DPSK modulated in accordance with §171.311(c)(1) and must be transmitted throughout the function coverage volume.
(2) Angle function formats. The timing of the angle transmissions must be in accordance with Tables 4a, 4b, and 5. The actual timing of the TO and FRO scans must be as required to meet the accuracy requirements of §§171.313 and 171.317.
(i) Preamble. Must be in accordance with requirements of §171.311(i)(1).
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Table 2_Preamble Timing \1\------------------------------------------------------------------------ Event time slot begins at_ ------------------------- 15.625 Event kHz clock Time pulse (milliseconds) (number)------------------------------------------------------------------------Carrier acquisition: (CW transmission)........................... 0 0Receiver reference time code: I1=1........................................ 13 0.832 I2=1........................................ 14 0.896 I3=1........................................ 15 0.960 I4=0........................................ 16 1.024 I5=1........................................ 17 \2\ 1.088Function identification: I6.......................................... 18 1.152 I7.......................................... 19 1.216 I8.......................................... 20 1.280 I9.......................................... 21 1.344 I10 (see table 1)........................... 22 1.408 I11......................................... 23 1.472 I12......................................... 24 1.536 END PREAMBLE................................ 25 1.600------------------------------------------------------------------------\1\ Applies to all functions transmitted.\2\ Reference time for receiver synchronization for all function timing.
Table 3_Function Identification Codes------------------------------------------------------------------------ Code Function ------------------------------ I6 I7 I8 I9 I10 I11 I12------------------------------------------------------------------------Approach azimuth......................... 0 0 1 1 0 0 1High rate approach azimuth............... 0 0 1 0 1 0 0Approach elevation....................... 1 1 0 0 0 0 1Back azimuth............................. 1 0 0 1 0 0 1Basic data 1............................. 0 1 0 1 0 0 0Basic data 2............................. 0 1 1 1 1 0 0Basic data 3............................. 1 0 1 0 0 0 0Basic data 4............................. 1 0 0 0 1 0 0Basic data 5............................. 1 1 0 1 1 0 0Dasic data 6............................. 0 0 0 1 1 0 1Auxiliary data A......................... 1 1 1 0 0 1 0Auxiliary data B......................... 1 0 1 0 1 1 1Auxiliary data C......................... 1 1 1 1 0 0 0------------------------------------------------------------------------
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(ii) Sector signals. In all azimuth formats, sector signals must be transmitted to provide Morse Code identification, airborne antenna selection, and system test signals. These signals are not required in the elevation formats. In addition, if the signal from an installed ground component results in a valid indication in an area where no valid guidance should exist, OCI signals must be radiated as provided for in the signal format (see Tables 4a, 4b, and 5). The sector signals are defined as follows:
(A) Morse Code. DPSK transmissions that will permit Morse Code facility identification in the aircraft by a four letter code starting with the letter “M” must be included in all azimuth functions. They must be transmitted and repeated at approximately equal intervals, not less than six times per minute, during which time the ground subsystem is available for operational use. When the transmissions of the ground subsystem are not available, the identification signal must be suppressed. The audible tone in the aircraft is started by setting the Morse Code bit to logic “1” and stopped by a logic “0” (see Tables 4a and 4b). The identification code characteristics must conform to the following: the dot must be between 0.13 and 0.16 second in duration, and the dash between 0.39 and 0.48 second. The duration between dots and/or dashes must be one dot plus or minus 10%. The duration between characters (letters) must not be less than three dots. When back azimuth is provided, the code shall be transmitted by the approach azimuth and back azimuth within plus or minus 0.08 seconds.
(B) Airborne antenna selection. A signal for airborne antenna selection shall be transmitted as a “zero” DPSK signal lasting for a six-bit period (see Tables 4a and 4b).
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Table 4a_Approach Azimuth Function timing------------------------------------------------------------------------ Event time slot begins at_ ------------------------- 15.625 Event kHz clock Time pulse (milliseconds) (number)------------------------------------------------------------------------Preamble...................................... 0 0Morse code.................................... 25 1.600Antenna select................................ 26 1.664Rear OCI...................................... 32 2.048Left OCI...................................... 34 2.176Right OCI..................................... 36 2.304To test....................................... 38 2.432To scan \1\................................... 40 2.560Pause......................................... ........ 8.760Midscan point................................. ........ 9.060FRO scan \1\.................................. ........ 9.360FRO test...................................... ........ 15.560End Function (Airborne)....................... ........ 15.688End guard time; end function (ground)......... ........ 15.900------------------------------------------------------------------------ AA\1\The actual commencement and completion of the TO and the FRO scan transmissions are dependent on the amount of proportional guidance provided. The time slots provided shall accommodate a maximum scan of plus or minus 62.0 degrees. Scan timing shall be compatible with accuracy requirements.
Table 4b_High Rate Approach Azimuth and Back Azimuth Function Timing------------------------------------------------------------------------ Event time slot begins at_ ------------------------- 15.625 Event kHz clock Time pulse (milliseconds) (number)------------------------------------------------------------------------Preamble...................................... 0 0Morse Code.................................... 25 1.600Antenna select................................ 26 1.664Rear OCI...................................... 32 2.048Left OCI...................................... 34 2.176Right OCI..................................... 36 2.304To test....................................... 38 2.432To scan \1\................................... 40 2.560Pause......................................... ........ 6.760Midscan point................................. ........ 7.060FRO scan \1\.................................. ........ 7.360FRO test pulse................................ ........ 11.560End function (airborne)....................... ........ 11.688End guard time; end function (ground)......... ........ 11.900------------------------------------------------------------------------\1\ The actual commencement and completion of the TO and the FRO scan transmissions are dependent on the amount of proportional guidance provided. The time slots provided will accommodate a maximum scan of plus or minus 42.0 degrees. Scan timing shall be compatible with accuracy requirements.
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(C) OCI. Where OCI pulses are used, they must be: (1) greater than any guidance signal in the OCI sector; (2) at least 5 dB less than the level of the scanning beam within the proportional guidance sector; and (3) for azimuth functions with clearance signals, at least 5 dB less than the level of the left (right) clearance pulses within the left (right) clearance sector.
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Table 5_Approach Elevation Function Timing------------------------------------------------------------------------ Event time slot begins at: ------------------------- 15.625 Event kHz clock Time pluse (milliseconds) (number)------------------------------------------------------------------------Preamble...................................... 0 0Processor pause............................... 25 1.600OCI........................................... 27 1.728To scan \1\................................... 29 1.856Pause......................................... ........ 3.406Midscan point................................. ........ 3.606FRO scan \1\.................................. ........ 3.806End function (airborne)....................... ........ 5.356End guard time; end function (ground)......... ........ 5.600------------------------------------------------------------------------\1\ The actual commencement and completion of the TO and FRO scan transmissions are dependent upon the amount of proportional guidance provided. The time slots provided will accommodate a maximum scan of - 1.5 degrees to +29.5 degrees. Scan timing shall be compatible with accuracy requirements.
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The duration of each pulse measured at the half amplitude point shall be at least 100 microseconds, and the rise and fall times shall be less then 10 microseconds. It shall be permissible to sequentially transmit two pulses in each out-of-coverage indication time slot. Where pulse pairs are used, the duration of each pulse shall be at least 50 microseconds, and the rise and fall times shall be less then 10 microseconds. The transmission of out-of-coverage indication pulses radiated from antennas with overlapping coverage patterns shall be separated by at least 10 microseconds.
Note: If desired, two pulses may be sequentially transmitted in each OCI time slot. Where pulse pairs are used, the duration of each pulse must be 45 (±5) microseconds and the rise and fall times must be less than 10 microseconds.
(D) System test. Time slots are provided in Tables 4a and 4b to allow radiation of TO and FRO test pulses. However, radiation of these pulses is not required since the characteristics of these pulses have not yet been standardized.
(iii) Angle encoding. The encoding must be as follows:
(A) General. Azimuth and elevation angles are encoded by scanning a narrow beam between the limits of the proportional coverage sector first in one direction (the TO scan) and then in the opposite direction (the FRO scan). Angular information must be encoded by the amount of time separation between the beam centers of the TO and FRO scanning beam pulses. The TO and FRO transmissions must be symmetrically disposed about the midscan point listed in Tables 4a, 4b, 5, and 7. The midscan point and the center of the time interval between the TO and FRO scan transmissions must coincide with a tolerance of ±10 microseconds. Angular coding must be linear with angle and properly decoded using the formula:
where:
Θ=Receiver angle in degrees.
V= Scan velocity in degrees per microsecond.
T0=Time separation in microseconds between TO and FRO beam centers corresponding to zero degrees.
t= Time separation in microseconds between TO and FRO beam centers.
The timing requirements are listed in Table 6 and illustrated in Figure 7.
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(B) Azimuth angle encoding. Each guidance angle transmitted must consist of a clockwise TO scan followed by a counterclockwise FRO scan as viewed from above the antenna. For approach azimuth functions, increasing angle values must be in the direction of the TO scan; for the back azimuth function, increasing angle values must be in the direction of the FRO scan. The antenna has a narrow beam in the plane of the scan direction and a broad beam in the orthogonal plane which fills the vertical coverage.
(C) Elevation angle encoding. The radiation from elevation equipment must produce a beam which scans from the horizon up to the highest elevation angle and then scans back down to the horizon. The antenna has a narrow beam in the plane of the scan direction and a broad beam in the orthogonal plane which fills the horizontal coverage. Elevation angles are defined from the horizontal plane containing the antenna phase center; positive angles are above the horizontal and zero angle is along the horizontal.
(iv) Clearance guidance. The timing of the clearance pulses must be in accordance with Figure 8. For azimuth elements with proportional coverage of less than ±40 degrees (±20 degrees for back azimuth), clearance guidance information must be provided by transmitting pulses in a TO and FRO format adjacent to the stop/start times of the scanning beam signal. The fly-right clearance pulses must represent positive angles and the fly-left clearance pulses must represent negative angles. The duration of each clearance pulse must be 50 microseconds with a tolerance of ±5 microseconds. The transmitter switching time between the clearance pulses and the scanning beam transmissions must not exceed 10 microseconds. The rise time at the edge of each clearance pulse must be less than 10 microseconds. Within the fly-right clearance guidance section, the fly-right clearance guidance signal shall exceed scanning beam antenna sidelobes and other guidance and OCI signals by at least 5 dB; within the fly-left clearance guidance sector, the fly left clearance guidance signal shall exceed scanning beam antenna sidelobes and all other guidance and OCI signals by at least 5 dB; within the proportional guidance sector, the clearance guidance signals shall be at least 5dB below the proportional guidance signal. Optionally, clearance guidance may be provided by scanning throughout the approach guidance sector. For angles outside the approach azimuth proportional coverage limits as set in Basic Data Word One (Basic Data Word 5 for back azimuth), proper decode and display of clearance guidance must occur to the limits of the guidance region. Where used, clearance pulses shall be transmitted adjacent to the scanning beam signals at the edges of proportional coverage as shown in Figure 8. The proportional coverage boundary shall be established at one beamwidth inside the scan start/stop angles, such that the transition between scanning beam and clearance signals occurs outside the proportional coverage sector. When clearance pulses are provided in conjunction with a narrow beamwidth (e.g., one degree) scanning antenna, the scanning beam antenna shall radiate for 15 microseconds while stationary at the scan start/stop angles.
(3) Data function format. Basic data words provide equipment characteristics and certain siting information. Basic data words must be transmitted from an antenna located at the approach azimuth or back azimuth site which provides coverage throughout the appropriate sector. Data function timing must be in accordance with Table 7a.
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Table 6_Angle Scan Timing Constants---------------------------------------------------------------------------------------------------------------- Max Pause Function value of To(usec) V(deg/ Tm time Tt t(usec) usec) (usec) (usec) (usec)----------------------------------------------------------------------------------------------------------------Approach azimuth.................................... 13,000 6,800 0.02 7,972 600 13,128High rate approach azimuth.......................... 9,000 4,800 0.02 5,972 600 9,128Approach elevation.................................. 3,500 3,350 0.02 2,518 400 N/ABack azimuth........................................ 9,000 4,800 -0.02 5,972 600 9,128----------------------------------------------------------------------------------------------------------------
Table 7a_Basic Data Function Timing------------------------------------------------------------------------ Event time slot begins at:\1\ ------------------------- 15.625 Event kHz clock Time pulse (milliseconds) (number)------------------------------------------------------------------------Preamble...................................... 0 0Data transmission (bits I13-I30).............. 25 1.600Parity transmission (bits I31-I32)............ 43 2.752End function (airborne)....................... 45 2.880End guard time: end function (ground)......... ........ 3.100------------------------------------------------------------------------\1\ The previous event time slot ends at this time.
Table 7b_Auxiliary Data Function Timing_(Digital)------------------------------------------------------------------------ Event time slot begins at: ------------------------- 15.625 Event kHz clock Time pulse (milliseconds) (number)------------------------------------------------------------------------Preamble...................................... 0 0Address transmission (bits I13-I20)........... 25 1.600Data transmission: (bits I21-I69)............. 33 2.112Parity transmission (bits I70-I76)............ 82 5.248End function (airborne)....................... 89 5.696End guard time; end function (ground)......... ........ 5.900------------------------------------------------------------------------
Table 7c_Auxiliary Data Function Timing_(Alphanumeric)------------------------------------------------------------------------ Event time slot begins at: ------------------------- 15.615 Event kHz clock Time pulse (milliseconds) (number)------------------------------------------------------------------------Preamble...................................... 0 0Address transmission (bits I13-I20)........... 25 1.600Data transmission: (bits I21-I76.............. 33 2.112End function (airborne)....................... 89 5.696End guard time; (end function ground)......... ........ 5.900------------------------------------------------------------------------
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(i) Preamble. Must be in accordance with requirements of §171.311(i)(1).
(ii) Data transmissions. Basic data must be transmitted using DPSK modulation. The content and repetition rate of each basic data word must be in accordance with Table 8a. For data containing digital information, binary number 1 must represent the lower range limit with increments in binary steps to the upper range limit shown in Table 8a. Data containing digital information shall be transmitted with the least significant bit first.
(j) Basic Data word requirements. Basic Data shall consist of the items specified in Table 8a. Basic Data word contents shall be defined as follows:
(1) Approach azimuth to threshold distance shall represent the minimum distance between the Approach Azimuth antenna phase center and the vertical plane perpendicular to the centerline which contains the landing threshold.
(2) Approach azimuth proportional coverage limit shall represent the limit of the sector in which proportional approach azimuth guidance is transmitted.
(3) Clearance signal type shall represent the type of clearance when used. Pulse clearance is that which is in accordance with §171.311 (i) (2) (iv). Scanning Beam (SB) clearance indicates that the proportional guidance sector is limited by the proportional coverage limits set in basic data.
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Table 8a_Basic Data Words------------------------------------------------------------------------ LSB Data bit # Data item definition value Data bit value------------------------------------------------------------------------ Basic Data Word No. 1------------------------------------------------------------------------1 Preamble................ N/A 12 ........................ ....... 13 ........................ ....... 14 ........................ ....... 05 ........................ ....... 16 ........................ ....... 07 ........................ ....... 18 ........................ ....... 09 ........................ ....... 110 ........................ ....... 011 ........................ ....... 012 ........................ ....... 013 Approach azimuth to 100m 100m threshold distance (Om- 630m).14 ........................ ....... 200m15 ........................ ....... 400m16 ........................ ....... 800m17 ........................ ....... 1600m18 ........................ ....... 3200m19 Approach azimuth 2° -2° proportional coverage limit (negative limit) (0° to -62°).20 ........................ ....... -4°21 ........................ ....... -8°22 ........................ ....... -16°23 ........................ ....... -32°24 Approach azimuth 2° 2° proportional coverage limit (positive limit) (0° to +62°).25 ........................ ....... 4°26 ........................ ....... 8°27 ........................ ....... 16°28 ........................ ....... 32°29 Clearance signal type... N/A 0=pulse; 1=SB30 Spare................... ....... Transmit zero31 Parity: (13+14+15. . N/A N/A .+30 +31=odd).32 Parity: (14+16+18. . N/A N/A .+30 +32=odd).Note 1: Transmit throughout the Approach Azimuth guidance sector at intervals of 1.0 seconds or less.Note 2: The all zero state of the data field represents the lower limit of the absolute value of the coded parameter unless otherwise noted.------------------------------------------------------------------------Basic Data Word No. 2------------------------------------------------------------------------1 Preamble................ N/A 12 ........................ ....... 13 ........................ ....... 14 ........................ ....... 05 ........................ ....... 16 ........................ ....... 07 ........................ ....... 18 ........................ ....... 19 ........................ ....... 110 ........................ ....... 111 ........................ ....... 012 ........................ ....... 013 Minimum glide path 0.1° 0.1° (2.0° to 14.7°). ;14 ........................ ....... 0.2°15 ........................ ....... 0.4°16 ........................ ....... 0.8°17 ........................ ....... 1.6°18 ........................ ....... 3.2°19 ........................ ....... 6.4°20 Back azimuth status..... ....... see note 421 DME status.............. ....... see note 622 ........................ ....... ....................23 Approach azimuth status. ....... see note 424 Approach azimuth status. ....... see note 425 Spare................... ....... Transmit zero26 ......do................ ....... Do.27 ......do................ ....... Do.28 ......do................ ....... Do.29 ......do................ ....... Do.30 ......do................ ....... Do.31 Parity: (13+14+15. . N/A N/A .+30 +31)=odd).32 Parity: (14+16+18. . N/A N/A .+30 +32=odd).Note 1: Transmit throughout the Approach Azimuth guidance sector at intervals of 0.16 seconds or less.Note 2: The all zero state of the data field represents the lower limit of the absolute range of the coded parameter unless otherwise noted.------------------------------------------------------------------------Basic Data Word No. 3------------------------------------------------------------------------1 Preamble................ N/A 12 ........................ ....... 13 ........................ ....... 14 ........................ ....... 05 ........................ ....... 16 ........................ ....... 17 ........................ ....... 08 ........................ ....... 19 ........................ ....... 010 ........................ ....... 011 ........................ ....... 012 ........................ ....... 013 Approach azimuth 0.5° 0.5° beamwidth (0.5°- ; 4.0°) See note 7.14 ........................ ....... 1.0°15 ........................ ....... 2.0°16 Approach elevation 0.5° 0.5° beamwidth (0.5° to ; 2.5°) See note 7.17 ........................ ....... 1.0°18 Note: values greater ....... 2.0° than 2.5° are invalid.19 DME distance (Om to 12.5m 12.5m 6387.5m.20 ........................ ....... 25.0m21 ........................ ....... 50.0m22 ........................ ....... 100.0m23 ........................ ....... 200.0m24 ........................ ....... 400.0m25 ........................ ....... 800.0m26 ........................ ....... 1600.0m27 ........................ ....... 3200.0m28 Spare................... ....... Transmit zero29 ......do................ ....... Do.30 ......do................ ....... Do.31 Parity: (13+14+15. . ....... .................... .+30 +31=odd).32 Parity: (14+16+18. . N/A N/A .+30 +32=odd).Note 1: Transmit throughout the Approach Azimuth guidance sector at intervals of 1.0 seconds or less.Note 2: The all zero state of the data field represents the lower limit of the absolute range of the coded parameter unless otherwise noted.------------------------------------------------------------------------Basic Data Word No. 4------------------------------------------------------------------------1 Preamble................ N/A 12 ........................ ....... 13 ........................ ....... 14 ........................ ....... 05 ........................ ....... 16 ........................ ....... 17 ........................ ....... 08 ........................ ....... 09 ........................ ....... 010 ........................ ....... 111 ........................ ....... 012 ........................ ....... 013 Approach azimuth 1° 1° magnetic orientation (0° to 359°).14 ........................ ....... 2°15 ........................ ....... 4°16 ........................ ....... 8°17 ........................ ....... 16°18 ........................ ....... 32°19 ........................ ....... 64°20 ........................ ....... 128°21 ........................ ....... 256°22 Back azimuth magnetic 1° 1° orientation (0° to 359°).23 ........................ ....... 2°24 ........................ ....... 4°25 ........................ ....... 8°26 ........................ ....... 16°27 ........................ ....... 32°28 ........................ ....... 64°29 ........................ ....... 128°30 ........................ ....... 256°31 Parity: (13+14+15. . N/A N/A .+30 +31=odd).32 Parity: (14+16+18. . N/A N/A .+30 +32=odd).Note 1: Transmit at intervals of 1.0 second or less throughout the Approach Azimuth guidance sector, except when Back Azimuth guidance is provided. See Note 8.Note 2: The all zero state of the data field represents the lower limit of the absolute range of the coded parameter unless otherwise noted.------------------------------------------------------------------------Basic Data Word No. 5------------------------------------------------------------------------1 Preamble................ N/A 12 ........................ ....... 13 ........................ ....... 14 ........................ ....... 05 ........................ ....... 16 ........................ ....... 17 ........................ ....... 18 ........................ ....... 09 ........................ ....... 110 ........................ ....... 111 ........................ ....... 012 ........................ ....... 013 Back azimuth 2° -2° proportional coverage negative limit (0° to -42°).14 ........................ ....... -4°15 ........................ ....... -8°16 ........................ ....... -16°17 ........................ ....... -32°18 Back azimuth 2° 2° proportional coverage positive limit (0° to +42°).19 ........................ ....... 4°20 ........................ ....... 8°21 ........................ ....... 16°22 ........................ ....... 32°23 Back azimuth beamwidth 0.5° 0.5° (0.5° to 4.0°) ; See note 7.24 ........................ ....... 1.0°25 ........................ ....... 2.0°26 Back azimuth status..... ....... See Note 1027 ......do................ ....... Do.28 ......do................ ....... Do.29 ......do................ ....... Do.30 ......do................ ....... Do.31 Parity: (13+14+15. . N/A N/A .+30 +31=odd).32 Parity: (14+16+18. . N/A N/A .+30 +32=odd).Note 1: Transmit only when Back Azimuth guidance is provided. See note 9.Note 2: The all zero state of the data filed represents the lower limit of the absolute range of the coded parameter unless otherwise noted.------------------------------------------------------------------------Basic Data Word No. 6------------------------------------------------------------------------1 Preamble................ N/A 12 ........................ ....... 13 ........................ ....... 14 ........................ ....... 05 ........................ ....... 16 ........................ ....... 07 ........................ ....... 08 ........................ ....... 09 ........................ ....... 110 ........................ ....... 111 ........................ ....... 012 ........................ ....... 1(13- MLS ground equipment ....... ....................30) identification (Note 3).13 Character 2............. N/A B114 ........................ ....... B215 ........................ ....... B316 ........................ ....... B417 ........................ ....... B518 ........................ ....... B619 Character 3............. N/A B120 ........................ ....... B221 ........................ ....... B322 ........................ ....... B423 ........................ ....... B524 ........................ ....... B625 Character 4............. N/A B126 ........................ ....... B227 ........................ ....... B328 ........................ ....... B429 ........................ ....... B530 ........................ ....... B631 Parity: (13+14+15. . N/A N/A .+30 +31=odd).32 Parity: (14+16+18. . N/A N/A .+30 +32=odd). Note 1: Transmit at intervals of 1.0 second or less throughout the Approach Azimuth guidance sector, except when Back Azimuth guidance is provided. See note 8. Note 3: Characters are encoded using the International Alphabet Number 5, (IA-5):Note 4: Coding for status bit:0=Function not radiated, or radiated in test mode (not reliable for navigation).1=Function radiated in normal mode (for Back Azimuth, this also indicates that a Back Azimuth transmission follows).Note 5: Date items which are not applicable to a particular ground equipment shall be transmitted as all zeros.Note 6: Coding for status bits:
I21 I22................ ...0 0.................. DME tra nsp ond er ino per ati ve or not ava ila ble .1 0.................. Onl y IA mod e or DME/ N ava ila ble .0 0.................. FA mod e, Sta nda rd 1, ava ila ble .1 1.................. FA mod e, Sta nda rd 2, ava ila ble . Note 7: The value coded shall be the actual beamwidth (as defined in § 171.311 (j)(9) rounded to the nearest 0.5 degree.Note 8: When back Azimuth guidance is provided, Data Words 4 and 6 shall be transmitted at intervals of 1.33 seconds or less throughout the Approach Azimuth coverage and 4 seconds or less throughout the Back Azimuth coverage.Note 9: When Back Azimuth guidance is provided, Data Word 5 shall be transmitted at an interval of 1.33 seconds or less throughout the Back Azimuth coverage sector and 4 seconds or less throughout the Approach Azimuth coverage sector.Note 10: Coding for status bit:0=Function not radiated, or radiated in test mode (not reliable for navigation).1=Function radiated in normal mode.
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(4) Minimum glidepath the lowest angle of descent along the zero degree azimuth that is consistent with published approach procedures and obstacle clearance criteria.
(5) Back azimuth status shall represent the operational status of the Back Azimuth equipment.
(6) DME status shall represent the operational status of the DME equipment.
(7) Approach azimuth status shall represent the operational status of the approach azimuth equipment.
(8) Approach elevation status shall represent the operational status of the approach elevation equipment.
(9) Beamwidth the width of the scanning beam main lobe measured at the -3 dB points and defined in angular units on the antenna boresight, in the horizontal plane for the azimuth function and in the vertical plane for the elevation function.
(10) DME distance shall represent the minimum distance between the DME antenna phase center and the vertical plane perpendicular to the runway centerline which contains the MLS datum point.
(11) Approach azimuth magnetic orientation shall represent the angle measured in the horizontal plane clockwise from Magnetic North to the zero-degree angle guidance radial originating from the approach azimuth antenna phase center. The vertex of the measured angle shall be at the approach azimuth antenna phase center.
Note: For example, this data item would be encoded 090 for an approach azimuth antenna serving runway 27 (assuming the magnetic heading is 270 degrees) when sited such that the zero degree radial is parallel to centerline.
(12) Back azimuth magnetic orientation shall represent the angle measured in the horizontal plane clockwise from Magnetic North to the zero-degree angle guidance radial originating from the Back Azimuth antenna. The vertex of the measured angle shall be at the Back Azimuth antenna phase center.
Note: For example, this data item would be encoded 270 for a Back Azimuth Antenna serving runway 27 (assuming the magnetic heading is 270 degrees) when sited such that the zero degree radial is parallel to centerline.
(13) Back azimuth proportional coverage limit shall represent the limit of the sector in which proportional back azimuth guidance is transmitted.
(14) MLS ground equipment identification shall represent the last three characters of the system identification specified in §171.311(i)(2). The characters shall be encoded in accordance with International Alphabet No. 5 (IA–5) using bits b1 through b6.
Note: Bit b7 of this code may be reconstructed in the airborne receiver by taking the complement of bit b6.
(k) Residual radiation. The residual radiation of a transmitter associated with an MLS function during time intervals when it should not be transmitting shall not adversely affect the reception of any other function. The residual radiation of an MLS function at times when another function is radiating shall be at least 70 dB below the level provided when transmitting.
(l) Symmetrical scanning. The TO and FRO scan transmissions shall be symmetrically disposed about the mid-scan point listed in Tables 4a, 4b and 5. The mid-scan point and the center of the time interval between the TO and FRO scan shall coincide with a tolerance of plus or minus 10 microseconds.
(m) Auxiliary data—(1) Addresses. Three function identification codes are reserved to indicate transmission of Auxiliary Data A, Auxiliary Data B, and Auxiliary Data C. Auxiliary Data A contents are specified below, Auxiliary Data B contents are reserved for future use, and Auxiliary Data C contents are reserved for national use. The address codes of the auxiliary data words shall be as shown in Table 8b.
(2) Organization and timing. The organization and timing of digital auxiliary data must be as specified in Table 7b. Data containing digital information must be transmitted with the least significant bit first. Alphanumeric data characters must be encoded in accordance with the 7-unit code character set as defined by the American National Standard Code for Information Interchange (ASCII). An even parity bit is added to each character. Alphanumeric data must be transmitted in the order in which they are to be read. The serial transmission of a character must be with the lower order bit transmitted first and the parity bit transmitted last. The timing for alphanumeric auxiliary data must be as shown in Table 7c.
(3) Auxiliary Data A content: The data items specified in Table 8c are defined as follows:
(i) Approach azimuth antenna offset shall represent the minimum distance between the Approach Azimuth antenna phase center and the vertical plane containing the runway centerline.
(ii) Approach azimuth to MLS datum point distance shall represent the minimum distance between the Approach Azimuth antenna phase center and the vertical plane perpendicular to the centerline which contains the MLS datum point.
(iii) Approach azimuth alignment with runway centerline shall represent the minimum angle between the approach azimuth antenna zero-degree guidance plane and the runway certerline.
(iv) Approach azimuth antenna coordinate system shall represent the coordinate system (planar or conical) of the angle data transmitted by the approach azimuth antenna.
(v) Approach elevation antenna offset shall represent the minimum distance between the elevation antenna phase center and the vertical plane containing the runway centerline.
(vi) MLS datum point to threshold distance shall represent the distance measured along the runway centerline from the MLS datum point to the runway threshold.
(vii) Approach elevation antenna height shall represent the height of the elevation antenna phase center relative to the height of the MLS datum point.
(viii) DME offset shall represent the minimum distance between the DME antenna phase center and the vertical plane containing the runway centerline.
(ix) DME to MLS datum point distance shall represent the minimum distance between the DME antenna phase center and the vertical plane perpendicular to the centerline which contains the MLS datum point.
(x) Back azimuth antenna offset shall represent the minimum distance between the back azimuth antenna phase center and the vertical plane containing the runway centerline.
(xi) Back azimuth to MLS datum point distance shall represent the minimum distance between the Back Azimuth antenna and the vertical plane perpendicular to the centerline which contains the MLS datum point.
(xii) Back azimuth antenna alignment with runway centerline shall represent the minimum angle between the back azimuth antenna zero-degree guidance plane and the runway centerline. § 171.313 Azimuth performance requirements.
This section prescribes the performance requirements for the azimuth equipment of the MLS as follows:
(a) Approach azimuth coverage requirements. The approach azimuth equipment must provide guidance information in at least the following volume of space (see Figure 9):
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Table 8b_Auxiliary Data Word Address Codes------------------------------------------------------------------------ No. I13 I14 I15 I16 I17 I18 I19 I20------------------------------------------------------------------------ 1. 0 0 0 0 0 1 1 1 2. 0 0 0 0 1 0 1 0 3. 0 0 0 0 1 1 0 1 4. 0 0 0 1 0 0 1 1 5. 0 0 0 1 0 1 0 0 6. 0 0 0 1 1 0 0 1 7. 0 0 0 1 1 1 1 0 8. 0 0 1 0 0 0 1 0 9. 0 0 1 0 0 1 0 1 10. 0 0 1 0 1 0 0 0 11. 0 0 1 0 1 1 1 1 12. 0 0 1 1 0 0 0 1 13. 0 0 1 1 0 1 1 0 14. 0 0 1 1 1 0 1 1 15. 0 0 1 1 1 1 0 0 16. 0 1 0 0 0 0 1 1 17. 0 1 0 0 0 1 0 0 18. 0 1 0 0 1 0 0 1 19. 0 1 0 0 1 1 1 0 20. 0 1 0 1 0 0 0 0 21. 0 1 0 1 0 1 1 1 22. 0 1 0 1 1 0 1 0 23. 0 1 0 1 1 1 0 1 24. 0 1 1 0 0 0 0 1 25. 0 1 1 0 0 1 1 0 26. 0 1 1 0 1 0 1 1 27. 0 1 1 0 1 1 0 0 28. 0 1 1 1 0 0 1 0 29. 0 1 1 1 0 1 0 1 30. 0 1 1 1 1 0 0 0 31. 0 1 1 1 1 1 1 1 32. 1 0 0 0 0 0 1 0 33. 1 0 0 0 0 1 0 1 34. 1 0 0 0 1 0 0 0 35. 1 0 0 0 1 1 1 1 36. 1 0 0 1 0 0 0 1 37. 1 0 0 1 0 1 1 0 38. 1 0 0 1 1 0 1 1 39. 1 0 0 1 1 1 0 0 40. 1 0 1 0 0 0 0 0 41. 1 0 1 0 0 1 1 1 42. 1 0 1 0 1 0 1 0 43. 1 0 1 0 1 1 0 1 44. 1 0 1 1 0 0 1 1 45. 1 0 1 1 0 1 0 0 46. 1 0 1 1 1 0 0 1 47. 1 0 1 1 1 1 1 0 48. 1 1 0 0 0 0 0 1 49. 1 1 0 0 0 1 1 0 50. 1 1 0 0 1 0 1 1 51. 1 1 0 0 1 1 0 0 52. 1 1 0 1 0 0 1 0 53. 1 1 0 1 0 1 0 1 54. 1 1 0 1 1 0 0 0 55. 1 1 0 1 1 1 1 1 56. 1 1 1 0 0 0 1 1 57. 1 1 1 0 0 1 0 0 58. 1 1 1 0 1 0 0 1 59. 1 1 1 0 1 1 1 0 60. 1 1 1 1 0 0 0 0 61. 1 1 1 1 0 1 1 1 62. 1 1 1 1 1 0 1 0 63. 1 1 1 1 1 1 0 1 64. 0 0 0 0 0 0 0 0------------------------------------------------------------------------
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Note 1: Parity bits I19 and I20 are chosen to satisfy the equations:
I13 + I14 + I15 + I16 + I17 + I18 + I19 = EVEN
I14 + I16 + I18 + I20 = EVEN
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Table 8c_Auxiliary Data-------------------------------------------------------------------------------------------------------------------------------------------------------- Maximun time between Bits Least Word (See note 6) Data content Type of data transmissions used Range of values significant (Seconds) bit--------------------------------------------------------------------------------------------------------------------------------------------------------A1.................................... Preamble................. Digital................. 1.0 12 ........................ ........... Address.................. ........................ ............. 8 ........................ ........... Approach azimuth antenna ........................ ............. 10 -511 m to +511 m (See 1 m offset. note 3). Approach azimuth to MLS ........................ ............. 13 0 m to 8 191 m.......... 1 m datum point distance. Approach azimuth antenna ........................ ............. 12 -20.47° to 0.01° alignment with runway 20.47° (See note 3). centerline. Approach azimuth antenna ........................ ............. 1 (See note 2)............ ........... coordinate system. Spare.................... ........................ ............. 13 ........................ ........... Parity................... ........................ ............. 7 (See note 1)............ ...........A2.................................... Preamble................. Digital................. 1.0 12 ........................ ........... Address.................. ........................ ............. 8 ........................ ........... Approach elevation ........................ ............. 10 -511 m to +511 m (See 1 m antenna offset. note 3). MLS datum point to ........................ ............. 10 0 m to 1 023 m.......... 1 m threshold distance. Approach elevation ........................ ............. 7 -6.3 m to +6.3 m (See 0.1 m antenna height. note 3). Spare.................... ........................ ............. 22 ........................ ........... Parity................... ........................ ............. 7 (See note 1)............ ...........A3.................................... Preamble................. Digital................. (See note 4) 12 ........................ ........... Address.................. ........................ ............. 8 ........................ ........... DME offset............... ........................ ............. 10 -511 m to +511 m........ 1 m DME to MLS datum point ........................ ............. 14 -8 191 m to +8 191 m 1 m distance. (See note 3). Spare.................... ........................ ............. 25 ........................ ........... Parity................... ........................ ............. 7 (See note 1)............ ...........A4.................................... Preamble................. Digital................. (See note 5) 12 ........................ ........... Address.................. ........................ ............. 8 ........................ ........... Back azimuth antenna..... ........................ ............. 10 -511 m to +511 m (See 1 m note 3). Back azimuth to MLS datum ........................ ............. 11 0 m to 2 047 m.......... 1 m point distance. Back azimuth antenna ........................ ............. 12 -20.47° to 0.01° alignment with runway 20.47° (See note 3). centerline. Spare.................... ........................ ............. 16 ........................ ........... Parity................... ........................ ............. 7 (See note 1)............ ...........--------------------------------------------------------------------------------------------------------------------------------------------------------
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Note 1: Parity bits I70 to I76 are chosen to satisfy the equations which follow:
For BIT I70:
Even = (I13 + ... + I18) + I20 + I22 + I24 + I25 + I28 + I29 + I31 + I32 + I33 + I35 + I36 + I38 + I41 + I44 + I45 + I46 + I50 + (I52 + ... + I55) + I58 + I60 + I64 + I65 + I70
For BIT I71:
Even = (I14 + ... + I19) + I21 + I23 + I25 + I26 + I29 + I30 + I32 + I33 + I34 + I36 + I37 + I39 + I42 + I45 + I46 + I47 + I51 + (I53 + ... + I56) + I59 + I61 + I65 + I66 + I71
For BIT I72:
Even = (I15 + ... + I20) + I22 + I24 + I26 + I27 + I30 + I31 + I33 + I34 + I35 + I37 + I38 + I40 + I43 + I46 + I47 + I48 + I52 + (I54 + ... + I57) + I60 + I62 + I66 + I67 + I72
For BIT I73:
Even = (I16 + ... + I21) + I23 + I25 + I27 + I28 + I31 + I32 + I34 + I35 + I36 + I38 + I39 + I41 + I44 + I47 + I48 + I49 + I53 + (I55 + ... + I58) + I61 + I63 + I67 + I68 + I73
For BIT I74:
Even = (I17 + ... + I22) + I24 + I26 + I28 + I29 + I32 + I33 + I35 + I36 + I37 + I39 + I40 + I42 + I45 + I48 + I49 + I50 + I54 + (I56 + ... + I59) + I62 + I64 + I68 + I69 + I74
For BIT I75:
Even = (I13 + ... + I17) + I19 + I21 + I23 + I24 + I27 + I28 + I30 + I31 + I32 + I34 + I35 + I37 + I40 + I43 + I44 + I45 + I49 + (I51 + ... + I54) + I57 + I59 + I63 + I64 + I69 + I75
For BIT I76:
Even = I13 + I14 + ... + I75 + I76
Note 2: Code for I56 is: 0 = conical; 1 = planar.
Note 3: The convention for the coding of negative numbers is as follows: − MSB is the sign bit; 0 = + ; 1 = −.
—Other bits represent the absolute value.
The convention for the antenna location is as follows: As viewed from the MLS approach reference datum looking toward the datum point, a positive number shall represent a location to the right of the runway centerline (lateral offset) or above the runway (vertical offset), or towards the stop end of the runway (longitudinal distance).
The convention for the antenna alignment is as follows: As viewed from above, a positive number shall represent clockwise rotation from the runway centerline to the respective zero-degree guidance plane.
Note 4: Data Word A3 is transmitted at intervals of 1.0 seconds or less throughout the approach Azimuth coverage sector, except when back Azimuth guidance is provided. Where back Azimuth is provided transmit at intervals of 1.33 seconds or less throughout the approach Azimuth sector and 4.0 seconds or less throughout the back Azimuth coverage sector.
Note 5: When back Azimuth guidance is provided, transmit at intervals of 1.33 seconds or less throughout the back Azimuth coverage sector and 4.0 seconds or less throughout the approach Azimuth coverage sector.
Note 6: The designation “A1” represents the function identification code for “Auxiliary Data A” and address code number 1.
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(1) Horizontally within a sector plus or minus 40 degrees about the runway centerline originating at the datum point and extending in the direction of the approach to 20 nautical miles from the runway threshold. The minimum proportional guidance sector must be plus or minus 10 degrees about the runway centerline. Clearance signals must be used to provide the balance of the required coverage, where the proportional sector is less than plus or minus 40 degrees. When intervening obstacles prevent full coverage, the ±40° guidance sector can be reduced as required. For systems providing ±60° lateral guidance the coverage requirement is reduced to 14 nm beyond ±40°.
(2) Vertically between:
(i) A conical surface originating 2.5 meters (8 feet) above the runway centerline at threshold inclined at 0.9 degree above the horizontal.
(ii) A conical surface originating at the azimuth ground equipment antenna inclined at 15 degrees above the horizontal to a height of 6,000 meters (20,000 feet).
(iii) Where intervening obstacles penetrate the lower surface, coverage need be provided only to the minimum line of sight.
(3) Runway region:
(i) Proportional guidance horizontally within a sector 45 meters (150 feet) each side of the runway centerline beginning at the stop end and extending parallel with the runway centerline in the direction of the approach to join the approach region. This requirement does not apply to offset azimuth installations.
(ii) Vertically between a horizontal surface which is 2.5 meters (8 feet) above the farthest point of runway centerline which is in line of sight of the azimuth antenna, and in a conical surface originating at the azimuth ground equipment antenna inclined at 20 degrees above the horizontal up to a height to 600 meters (2,000 feet). This requirement does not apply to offset azimuth installations.
(4) Within the approach azimuth coverage sector defined in paragraphs (a) (1), and (2) and (3) of this section, the power densities must not be less than those shown in Table 9 but the equipment design must also allow for:
(i) Transmitter power degradation from normal by −1.5 dB;
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Table 9_Minimum Power Density Within Coverage Boundaries(dBW/m\2\)---------------------------------------------------------------------------------------------------------------- Angle signals for various antenna Data beamwidths Clearance Function signals -------------------------------------- signals 1° 1.5° 2° 3°----------------------------------------------------------------------------------------------------------------Approach azimuth................................... -89.5 -88 ........ -85.5 -82 -88High rate approach azimuth......................... -89.5 -88 ........ -88 -86.5 -88Back azimuth....................................... -89.5 -88 ........ -85.5 -82 -88Approach elevation................................. -89.5 -88 -88 -88 ........ ...........----------------------------------------------------------------------------------------------------------------
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(ii) Rain loss of −2.2 dB at the longitudinal coverage extremes.
(b) Siting requirements. The approach azimuth antenna system must, except as allowed in paragraph (c) of this section:
(1) Be located on the extension of the centerline of the runway beyond the stop end;
(2) Be adjusted so that the zero degree azimuth plane will be a vertical plane which contains the centerline of the runway served;
(3) Have the minimum height necessary to comply with the coverage requirements prescribed in paragraph (a) of this section;
(4) Be located at a distance from the stop end of the runway that is consistent with safe obstruction clearance practices;
(5) Not obscure any light of an approach lighting system; and
(6) Be installed on frangible mounts or beyond the 300 meter (1,000 feet) light bar.
(c) On runways where limited terrain prevents the azimuth antenna from being positioned on the runway centerline extended, and the cost of the land fill or a tall tower antenna support is prohibitive, the azimuth antenna may be offset.
(d) Antenna coordinates. The scanning beams transmitted by the approach azimuth equipment within ±40° of the centerline may be either conical or planar.
(e) Approach azimuth accuracy. (1) The system and subsystem errors shall not exceed those listed in Table 10 at the approach reference datum.
At the approach reference datum, temporal sinusoidal noise components shall not exceed 0.025 degree peak in the frequency band 0.01 Hz to 1.6 Hz, and the CMN shall not exceed 0.10 degree. From the approach reference datum to the coverage limit, the PFE, PFN and CMN limits, expressed in angular terms, shall be allowed to linearly increase as follows:
(i) With distance along the runway centerline extended, by a factor of 1.2 for the PFE and PFN limits and to ±0.10 degree for the CMN limits.
(ii) With azimuth angle, by a factor of 1.5 at the ±40 degree and a factor of 2.0 at the ±60 degree azimuth angles for the PFE, PFN and CMN limits.
(iii) With elevation angle from +9 degrees to +15 degrees, by a factor of 1.5 for the PFE and PFN limits.
(iv) Maximum angular limits. The PFE limits shall not exceed ±0.25 degree in any coverage region below an elevation angle of +9 degrees nor exceed ±0.50 degree in any coverage region above that elevation angle. The CMN limits shall not exceed ±0.10 degree in any coverage region within ±10 degrees of runway centerline extended nor exceed ±0.20 degree in any other region within coverage.
Note: It is desirable that the CMN not exceed ±0.10 degree throughout the coverage.
(f) Approach azimuth antenna characteristics are as follows:
(1) Drift. Any azimuth angle as encoded by the scanning beam at any point within the proportional coverage must not vary more than ±0.07 degree over the range of service conditions specified in §171.309(d) without the use of internal environmental controls. Multipath effects are excluded from this requirement.
(2) Beam pointing errors. The azimuth angle as encoded by the scanning beam at any point within ±0.5 degree of the zero degree azimuth must not deviate from the true azimuth angle at that point by more than ±.05 degree. Multipath and drift effects are excluded from this requirement.
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Table 10_Approach Azimuth Accuracies at the Approach Reference Datum---------------------------------------------------------------------------------------------------------------- Angular error (degrees) Error type System ----------------------------------------- Ground subsystem Airborne subsystem----------------------------------------------------------------------------------------------------------------PFE................................... ±20 ft. (6.1m) 1,2 ±0.118° ±0.017° \3\.CMN................................... ±10.5 ft. (3.2m) 1,2,4 ±0.030°. ±0.050°----------------------------------------------------------------------------------------------------------------Notes:\1\ Includes errors due to ground and airborne equipment and propagation effects.\2\ The system PFN component must not exceed ±3.5 meters (11.5 feet).\3\ The mean (bias) error component contributed by the ground equipment should not exceed ±10 feet.\4\ The system control motion noise must not exceed 0.1 degree.\5\ The airborne subsystem angular errors are provided for information only.
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(3) Antenna alignment. The antenna must be equipped with suitable optical, electrical or mechanical means or any combination of the three, to bring the zero degree azimuth radial into coincidence with the approach reference datum (for centerline siting) with a maximum error of 0.02 degree. Additionally, the azimuth antenna bias adjustment must be electronically steerable at least to the monitor limits in steps not greater than 0.005 degree.
(4) Antenna far field patterns in the plane of scan. On boresight, the azimuth antenna mainlobe pattern must conform to Figure 10, and the beamwidth must be such that, in the installed environment, no significant lateral reflections of the mainlobe exist along the approach course. In any case the beamwidth must not exceed three degrees. Anywhere within coverage the −3 dB width of the antenna mainlobe, while scanning normally, must not be less than 25 microseconds (0.5 degree) or greater than 250 microseconds (5 degrees). The antenna mainlobe may be allowed to broaden from the value at boresight by a factor of 1/cosΘ, where Θ is the angle off boresight. The sidelobe levels must be as follows:
(i) Dynamic sidelobe levels. With the antenna scanning normally, the dynamic sidelobe level that is detected by a receiver at any point within the proportional coverage sector must be down at least 10 dB from the peak of the main beam. Outside the coverage sector, the radiation from the scanning beam antenna must be of such a nature that receiver warning will not be removed or suitable OCI signals must be provided.
(ii) Effective sidelobe levels. With the antenna scanning normally, the sidelobe levels in the plane of scan must be such that, in the installed environment, the CMN contributed by sidelobe reflections will not exceed the angular equivalent of 9 feet at approach reference datum over the required range of aircraft approach speeds.
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(5) Antenna far field pattern in the vertical plane. The azimuth antenna free space radiation pattern below the horizon must have a slope of at least −8 dB/degree at the horizon and all sidelobes below the horizon must be at least 13 dB below the pattern peak. The antenna radiation pattern above the horizon must satisfy both the system coverage requirements and the spurious radiation requirement.
(6) Data antenna. The data antenna must have horizontal and vertical patterns as required for its function.
(g) Back azimuth coverage requirements. The back azimuth equipment where used must provide guidance information in at least the following volume of space (see Figure 11):
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(1) Horizontally within a sector ±40 degrees about the runway centerline originating at the back azimuth ground equipment antenna and extending in the direction of the missed approach at least to 20 nautical miles from the runway stop end. The minimum proportional guidance sector must be ±10 degrees about the runway centerline. Clearance signals must be used to provide the balance of the required coverage where the proportional sector is less than ±40 degrees.
(2) Vertically in the runway region between:
(i) A horizontal surface 2.5 meters (8 feet) above the farthest point of runway centerline which is in line of sight of the azimuth antenna, and,
(ii) A conical surface originating at the azimuth ground equipment antenna inclined at 20 degrees above the horizontal up to a height of 600 meters (2000 feet).
(3) Vertically in the back azimuth region between:
(i) A conical surface originating 2.5 meters (8 feet) above the runway stop end, included at 0.9 degree above the horizontal, and,
(ii) A conical surface orginating at the missed approach azimuth ground equipment antenna, inclined at 15 degrees above the horizontal up to a height of 1500 meters (5000 feet).
(iii) Where obstacles penetrate the lower coverage limits, coverage need be provided only to minimum line of sight.
(4) Within the back azimuth coverage sector defined in paragraph (q) (1), (2), and (3) of this section the power densities must not be less than those shown in Table 9, but the equipment design must also allow for:
(i) Transmitter power degradation from normal −1.5 dB.
(ii) Rain loss of −2.2 dB at the longitudinal coverage extremes.
(h) Back azimuth siting. The back azimuth equipment antenna must:
(1) Normally be located on the extension of the runway centerline at the threshold end;
(2) Be adjusted so that the vertical plane containing the zero degree course line contains the back azimuth reference datum;
(3) Have minimum height necessary to comply with the course requirements prescribed in paragraph (g) of this section;
(4) Be located at a distance from the threshold end that is consistent with safe obstruction clearance practices;
(5) Not obscure any light of an approach lighting system; and
(6) Be installed on frangible mounts or beyond the 300 meter (1000 feet) light bar.
(i) Back azimuth antenna coordinates. The scanning beams transmitted by the back azimuth equipment may be either conical or planar.
(j) Back azimuth accuracy. The requirements specified in §171.313(e) apply except that the reference point is the back azimuth reference datum.
(k) Back azimuth antenna characteristics. The requirements specified in §171.313(f) apply.
(l) Scanning conventions. Figure 12 shows the approach azimuth and back azimuth scanning conventions.
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(m) False guidance. False courses which can be acquired and tracked by an aircraft shall not exist anywhere either inside or outside of the MLS coverage sector. False courses which exist outside of the minimum coverage sector may be suppressed by the use of OCI.
Note: False courses may be due to (but not limited to) MLS airborne receiver acquisition of the following types of false guidance: reflections of the scanning beam, scanning beam antenna sidelobes and grating lobes, and incorrect clearance.
§ 171.315 Azimuth monitor system requirements.
(a) The approach azimuth or back azimuth monitor system must cause the radiation to cease and a warning must be provided at the designated control point if any of the following conditions persist for longer than the periods specified:
(1) There is a change in the ground equipment contribution to the mean course error component such that the path following error at the reference datum or in the direction of any azimuth radial, exceeds the limits specified in §§171.313(e)(1) or 171.313(j) for a period of more than one second.
Note: The above requirement and the requirement to limit the ground equipment mean error to ±10 ft. can be satisfied by the following procedure. The integral monitor alarm limit should be set to the angular equivalent of ±10 ft. at the approach reference datum. This will limit the electrical component of the mean course error to ±10 ft. The field monitor alarm limit should be set such that with the mean course error at the alarm limit the total allowed PFE is not exceeded on any commissioned approach course from the limit of coverage to an altitude of 100 feet.
(2) There are errors in two consecutive transmissions of Basic Data Words 1, 2, 4 or 5.
(3) There is a reduction in the radiated power to a level not less than that specified in §§171.313(a)(4) or 171.313(g)(4) for a period of more than one second.
(4) There is an error in the preamble DPSK transmissions which occurs more than once in any one second period.
(5) There is an error in the time division multiplex synchronization of a particular azimuth function that the requirement specified in §171.311(e) is not satisfied and if this condition persists for more than one second.
(6) A failure of the monitor is detected.
(b) Radiation of the following fuctions must cease and a warning provided at the designated control point if there are errors in 2 consecutive transmissions:
(1) Morse Code Identification,
(2) Basic Data Words 3 and 6,
(3) Auxiliary Data Words.
(c) The period during which erroneous guidance information is radiated must not exceed the periods specified in §171.315(a). If the fault is not cleared within the time allowed, the ground equipment must be shut down. After shutdown, no attempt must be made to restore service until a period of 20 seconds has elapsed. § 171.317 Approach elevation performance requirements.
This section prescribes the performance requirements for the elevation equipment components of the MLS as follows:
(a) Elevation coverage requirements. The approach elevation facility must provide proportional guidance information in at least the following volume of space (see Figure 13):
(1) Laterally within a sector originating at the datum point which is at least equal to the proportional guidance sector provided by the approach azimuth ground equipment.
(2) Longitudinally from 75 meters (250 feet) from the datum point to 20 nautical miles from threshold in the direction of the approach.
(3) Vertically within the sector bounded by:
(i) A surface which is the locus of points 2.5 meters (8 feet) above the runway surface;
(ii) A conical surface originating at the datum point and inclined 0.9 degree above the horizontal and,
(iii) A conical surface originating at the datum point and inclined at 15.0 degrees above the horizontal up to a height of 6000 meters (20,000 feet).
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Where the physical characteristics of the approach region prevent theachievement of the standards under paragraphs (a) (1), (2), and (3) of this section, guidance need not be provided below a conical surface originating at the elevation antenna and inclined 0.9 degree above the line of sight.
(4) Within the elevation coverage sector defined in paragraphs (a) (1), (2) and (3) of this section, the power densities must not be less than those shown in Table 9, but the equipment design must also allow for:
(i) Transmitter power degradation from normal by −1.5 dB.
(ii) Rain loss of −2.2 dB at the coverage extremes.
(b) Elevation siting requirements. The Elevation Antenna System must:
(1) Be located as close to runway centerline as possible (without violating obstacle clearance criteria).
(2) Be located near runway threshold such that the asymptote of the minimum glidepath crosses the threshold of the runway at the Approach Reference Datum height. Normally, the minimum glidepath should be 3 degrees and the Approach Reference Datum height should be 50 feet. However, there are circumstances where other glideslopes and reference datum heights are appropriate. Some of these instances are discussed in FAA Order 8260.34 (Glide Slope Threshold Crossing Height Requirements) and Order 8260.3 (IFR Approval of MLS.)
(3) Be located such that the MLS Approach Reference Datum and ILS Reference Datum heights are coincident within a tolerance of 3 feet when MLS is installed on a runway already served by an ILS. This requirement applies only if the ILS glide slope is sited such that the height of the reference datum meets the requirements of FAA Order 8260.34.
(c) Antenna coordinates. The scanning beams transmitted by the elevation subsystem must be conical.
(d) Elevation accuracy. (1) The accuracies shown in Table 13 are required at the approach reference datum. From the approach reference datum to the coverage limit, the PFE, PFN and CMN limits shall be allowed to linearly increase as follows:
(i) With distance along the runway centerline extended at the minimum glide path angle, by a factor of 1.2 for the PFE and PFN limits and to ±0.10 degree for the CMN limits;
(ii) With azimuth angle, from runway centerline extended to the coverage extreme, by a factor of 1.2 for the PFE and PFN limits and by a factor of 2.0 for the CMN limits;
(iii) With increasing elevation angles from +3 degrees to +15 degrees, by a factor of 2.0 for the PFE and PFN limits;
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Table 13_Elevation Accuracies at the Approach Reference Datum------------------------------------------------------------------------ Angular error (degrees) ------------------------- Error type System Airborne Ground subsystem subsystem \4\------------------------------------------------------------------------PFE.............................. \1,2\ (\3\) ±0.0 ±0.1 17 33CMN.............................. \1\± ±0.0 ±0.0 0.050 20 10------------------------------------------------------------------------Notes:\1\ Includes errors due to ground and airborne equipment and propagation effects.\2\ The system PFN component must not exceed ±0.087 degree.\3\ The mean (bias) error component contributed by the ground equipment should not exceed ±0.067 degree.\4\ The airborne subsystem angular errors are provided for information only.
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(iv) With decreasing elevation angle from +3 degrees (or 60% of the minimum glide path angle, whichever is less) to the coverage extreme, by a factor of 3 for the PFE, PFN and CMN limits; and
(v) Maximum angular limits. the CMN limits shall not exceed ±0.10 degree in any coverage region within ±10 degrees laterally of runway centerline extended which is above the elevation angle specified in (iv) above.
Note: It is desirable that the CMN not exceed ±0.10 degree throughout the coverage region above the elevation angle specified in paragraph (d)(1)(iv) of this section.
(2) The system and ground subsystem accuracies shown in Table 13 are to be demonstrated at commissioning as maximum error limits. Subsequent to commissioning, the accuracies are to be considered at 95% probability limits.
(e) Elevation antenna characteristics are as follows:
(1) Drift. Any elevation angle as encoded by the scanning beam at any point within the coverage sector must not vary more than 0.04 degree over the range of service conditions specified in §171.309(d) without the use of internal environmental controls. Multipath effects are excluded from this requirement.
(2) Beam pointing errors. The elevation angle as encoded by the scanning beam at any point within the coverage sector must not deviate from the true elevation angle at that point by more than ±0.04 degree for elevation angles from 2.5° to 3.5°. Above 3.5° these errors may linearly increase to ±0.1 degree at 7.5°. Multipath and drift effects are excluded from this requirement.
(3) Antenna alignment. The antenna must be equipped with suitable optical, electrical, or mechanical means or any combination of the three, to align the lowest operationally required glidepath to the true glidepath angle with a maximum error of 0.01 degree. Additionally, the elevation antenna bias adjustment must be electronically steerable at least to the monitor limits in steps not greater than 0.005 degrees.
(4) Antenna far field patterns in the plane of scan. On the lowest operationally required glidepath, the antenna mainlobe pattern must conform to Figure 10, and the beamwidth must be such that in the installed environment, no significant ground reflections of the mainlobe exist. In any case, the beamwidth must not exceed 2 degrees. The antenna mainlobe may be allowed to broaden from the value at boresight by a factor of 1/cosΘ, where Θ is the angle of boresight. Anywhere within coverage, the −3 dB width of the antenna mainlobe, while scanning normally, must not be less than 25 microseconds (0.5 degrees) or greater than 250 microseconds (5 degrees). The sidelobe levels must be as follows:
(i) Dynamic sidelobe levels. With the antenna scanning normally, the dynamic sidelobe level that is detected by a receiver at any point within the proportional coverage sector must be down at least 10 dB from the peak of the mainlobe. Outside the proportional coverage sector, the radiation from the scanning beam antenna must be of such a nature that receiver warnings will not be removed or a suitable OCI signal must be provided.
(ii) Effective sidelobe levels. With the antenna scanning normally, the sidelobe levels in the plane of scan must be such that, when reflected from the ground, the resultant PFE along any glidepath does not exceed 0.083 degrees.
(5) Antenna far field pattern in the horizontal plane. The horizontal pattern of the antenna must gradually de-emphasize the signal away from antenna boresight. Typically, the horizontal pattern should be reduced by at least 3 dB at 20 degrees off boresight and by at least 6 dB at 40 degrees off boresight. Depending on the actual multipath conditions, the horizontal radiation patterns may require more or less de-emphasis.
(6) Data antenna. The data antenna must have horizontal and vertical patterns as required for its function.
(f) False guidance. False courses which can be acquired and tracked by an aircraft shall not exist anywhere either inside or outside of the MLS coverage sector. False courses which exist outside of the minimum coverage sector may be suppressed by the use of OCI.
Note: False courses may be due to (but not limited to) MLS airborne receiver acquisition of the following types of false guidance: reflections of the scanning beam and scanning beam antenna sidelobes and grating lobes.
§ 171.319 Approach elevation monitor system requirements.
(a) The monitor system must act to ensure that any of the following conditions do not persist for longer than the periods specified when:
(1) There is a change in the ground component contribution to the mean glidepath error component such that the path following error on any glidepath exceeds the limits specified in §171.317(d) for a period of more than one second.
Note: The above requirement and the requirement to limit the ground equipment mean error to ±0.067 degree can be satisfied by the following procedure. The integral monitor alarm limit should be set to ±0.067 degree. This will limit the electrical component of mean glidepath error to ±0.067 degree. The field monitor alarm limit should be set such that with the mean glidepath error at the alarm limit the total allowed PFE is not exceeded on any commissioned glidepath from the limit of coverage to an altitude of 100 feet.
(2) There is a reduction in the radiated power to a level not less than that specified in §171.317(a)(4) for a period of more than one second.
(3) There is an error in the preamble DPSK transmission which occurs more than once in any one second period.
(4) There is an error in the time division multiplex synchronization of a particular elevation function such that the requirement specified in §171.311(e) is not satisfied and this condition persists for more than one second.
(5) A failure of the monitor is detected.
(b) The period during which erroneous guidance information is radiated must not exceed the periods specified in §171.319(a). If the fault is not cleared within the time allowed, radiation shall cease. After shutdown, no attempt must be made to restore service until a period of 20 seconds has elapsed. § 171.321 DME and marker beacon performance requirements.
(a) The DME equipment must meet the performance requirements prescribed in subpart G of the part. This subpart imposes requirements that performance features must comply with International Standards and Recommended Practices, Aeronautical Telecommunications, Vol. I of Annex 10 to ICAO. It is available from ICAO, Aviation Building, 1080 University Street, Montreal 101, Quebec, Canada, Attention: Distribution Officer and also available for inspection at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, call 202–741–6030, or go to: http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.php.
(b) MLS marker beacon equipment must meet the performance requirements prescribed in subpart H of this part. This subpart imposes requirements that performance features must comply with International Standards and Recommended Practices, Aeronautical Telecommuncations, Vol. I of Annex 10 to ICAO.
[Doc. No. 5034, 29 FR 11337, Aug. 6, 1964, as amended at 69 FR 18803, Apr. 9, 2004] § 171.323 Fabrication and installation requirements.
(a) The MLS facility must be permanent and must be located, constructed, and installed in accordance with best commercial engineering practices, using applicable electric and safety codes and Federal Communications Commission (FCC) licensing requirements and siting requirements of §§171.313(b) and 171.317(b).
(b) The MLS facility components must utilize solid state technology except that traveling wave tube amplifiers (TWTA) may be used. A maximum level of common modularity must be provided along with diagnostics to facilitate maintenance and troubleshooting.
(c) An approved monitoring capability must be provided which indicates the status of the equipment at the site and at a remotely located maintenance area, with monitor capability that provides pre-alarm of impending system failures. This monitoring feature must be capable of transmitting the status and pre-alarm over standard phone lines to a remote section. In the event the sponsor requests the FAA to assume ownership of the facility, the monitoring feature must also be capable of interfacing with FAA remote monitoring requirements. This requirement may be complied with by the addition of optional software and/or hardware in space provided in the original equipment.
(d) The mean corrective maintenance time of the MLS equipment must be equal to or less than 0.5 hours with a maximum corrective maintenance time not to exceed 1.5 hours. This measure applies to correction of unscheduled failures of the monitor, transmitter and associated antenna assemblies, limited to unscheduled outage and out of tolerance conditions.
(e) The mean-time-between-failures of the MLS angle system must not be less than 1,500 hours. This measure applies to unscheduled outage, out-of-tolerance conditions, and failures of the monitor, transmitter, and associated antenna assemblies.
(f) The MLS facility must have a reliable source of suitable primary power, either from a power distribution system or locally generated. Adequate power capacity must be provided for the operation of the MLS as well as the test and working equipment of the MLS.
(g) The MLS facility must have a continuously engaged or floating battery power source for the continued normal operation of the ground station operation if the primary power fails. A trickle charge must be supplied to recharge the batteries during the period of available primary power. Upon loss and subsequent restoration of power, the battery must be restored to full charge within 24 hours. When primary power is applied, the state of the battery charge must not affect the operation of the MLS ground station. The battery must allow continuation of normal operation of the MLS facility for at least 2 hours without the use of additional sources of power. When the system is operating from the battery supply without prime power, the radome deicers and the environmental system need not operate. The equipment must meet all specification requirements with or without batteries installed.
(h) There must be a means for determining, from the ground, the performance of the system including antenna, both initially and periodically.
(i) The facility must have, or be supplemented by, ground, air, or landline communications services. At facilities within or immediately adjacent to controlled airspace, that are intended for use as instrument approach aids for an airport, there must be ground air communications or reliable communications (at least a landline telephone) from the airport to the nearest FAA air traffic control or communication facility. Compliance with this paragraph need not be shown at airports where an adjacent FAA facility can communicate with aircraft on the ground at the airport and during the entire proposed instrument approach procedure. In addition, at low traffic density airports within or immediately adjacent to controlled airspace, and where extensive delays are not a factor, the requirements of this paragraph may be reduced to reliable communications from the airport to the nearest FAA air traffic control or communications facility. If the adjacent FAA facility can communicate with aircraft during the proposed instrument approach procedure down to the airport surface or at least down to the minimum en route altitude, this would require at least a landline telephone.
(j) The location of the phase center for all antennas must be clearly marked on the antenna enclosures.
(k) The latitude, longitude and mean sea level elevation of all MLS antennas, runway threshold and runway stop end must be determined by survey with an accuracy of ±3 meters (±10 feet) laterally and ±0.3 meter (±1.0 foot) vertically. The relative lateral and vertical offsets of all antenna phase centers, and both runway ends must be determined with an accuracy of ±0.3 meter (±1.0 foot) laterally and ±0.03 meter (±0.1 foot) vertically. The owner must bear all costs of the survey. The results of this survey must be included in the “operations and maintenance” manual required by section 171.325 of this subpart and will be noted on FAA Form 198 required by §171.327.
[Doc. No. 20669, 51 FR 33177, Sept. 18, 1986, as amended by Amdt. 171–16, 56 FR 65665, Dec. 17, 1991] § 171.325 Maintenance and operations requirements.
(a) The owner of the facility must establish an adequate maintenance system and provide MLS qualified maintenance personnel to maintain the facility at the level attained at the time it was commissioned. Each person who maintains a facility must meet the FCC licensing requirements and demonstrate that he has the special knowledge and skills needed to maintain an MLS facility, including proficiency in maintenance procedures and the use of specialized test equipment.
(b) In the event of out-of-tolerance conditions or malfunctions, as evidenced by receiving two successive pilot reports, the owner must close the facility by encasing radiation, and issue a “Notice to Airmen” (NOTAM) that the facility is out of service.
(c) The owner must prepare, and obtain approval of, an operations and maintenance manual that sets forth mandatory procedures for operations, periodic maintenance, and emergency maintenance, including instructions on each of the following:
(1) Physical security of the facility.
(2) Maintenance and operations by authorized persons.
(3) FCC licensing requirements for operations and maintenance personnel.
(4) Posting of licenses and signs.
(5) Relations between the facility and FAA air traffic control facilities, with a description of the boundaries of controlled airspace over or near the facility, instructions for relaying air traffic control instructions and information, if applicable, and instructions for the operation of an air traffic advisory service if the facility is located outside of controlled airspace.
(6) Notice to the Administrator of any suspension of service.
(7) Detailed and specific maintenance procedures and servicing guides stating the frequency of servicing.
(8) Air-ground communications, if provided, expressly written or incorporating appropriate sections of FAA manuals by reference.
(9) Keeping the station logs and other technical reports, and the submission of reports required by §171.327.
(10) Monitoring of the MLS facility.
(11) Inspections by United States personnel.
(12) Names, addresses, and telephone numbers of persons to be notified in an emergency.
(13) Shutdowns for periodic maintenance and issuing of NOTAM for routine or emergency shutdowns.
(14) Commissioning of the MLS facility.
(15) An acceptable procedure for amending or revising the manual.
(16) An explanation of the kinds of activities (such as construction or grading) in the vicinity of the MLS facility that may require shutdown or recertification of the MLS facility by FAA flight check.
(17) Procedures for conducting a ground check of the azimuth and elevation alignment.
(18) The following information concerning the MLS facility:
(i) Facility component locations with respect to airport layout, instrument runways, and similar areas.
(ii) The type, make and model of the basic radio equipment that provides the service including required test equipment.
(iii) The station power emission, channel, and frequency of the azimuth, elevation, DME, marker beacon, and associated compass locators, if any.
(iv) The hours of operation.
(v) Station identification call letters and method of station identification and the time spacing of the identification.
(vi) A description of the critical parts that may not be changed, adjusted, or repaired without an FAA flight check to confirm published operations.
(d) The owner or his maintenance representative must make a ground check of the MLS facility periodically in accordance with procedures approved by the FAA at the time of commissioning, and must report the results of the checks as provided in §171.327.
(e) The only modifications permitted are those that are submitted to FAA for approval by the MLS equipment manufacturer. The owner or sponsor of the facility must incorporate these modifications in the MLS equipment. Associated changes must also be made to the operations and maintenance manual required in paragraph (c) of this section. This and all other corrections and additions to this operations and maintenance manual must also be submitted to FAA for approval.
(f) The owner or the owner's maintenance representative must participate in inspections made by the FAA.
(g) The owner must ensure the availability of a sufficient stock of spare parts, including solid state components, or modules to make possible the prompt replacement of components or modules that fail or deteriorate in service.
(h) FAA approved test instruments must be used for maintenance of the MLS facility.
(i) Inspection consists of an examination of the MLS equipment to ensure that unsafe operating conditions do not exist.
(j) Monitoring of the MLS radiated signal must ensure a high degree of integrity and minimize the requirements for ground and flight inspection. The monitor must be checked daily during the in-service test evaluation period (96 hour burn in) for calibration and stability. These tests and ground checks or azimuth, elevation, DME, and marker beacon radiation characteristics must be conducted in accordance with the maintenance requirements of this section. § 171.327 Operational records.
The owner of the MLS facility or his maintenance representative must submit the following operational records at the indicated time to the appropriate FAA regional office where the facility is located.
(a) Facility Equipment Performance & Adjustment Data (FAA Form 198). The FAA Form 198 shall be filled out by the owner or his maintenance representative with the equipment adjustments and meter readings as of the time of facility commissioning. One copy must be kept in the permanent records of the facility and two copies must be sent to the appropriate FAA regional office. The owner or his maintenance representative must revise the FAA Form 198 data after any major repair, modernization, or retuning to reflect an accurate record of facility operation and adjustment.
(b) Facility Maintenance Log (FAA Form 6030–1). FAA Form 6030–1 is permanent record of all the activities required to maintain the MLS facility. The entries must include all malfunctions met in maintaining the facility including information on the kind of work and adjustments made, equipment failures, causes (if determined) and corrective action taken. In addition, the entries must include completion of periodic maintenance required to maintain the facility. The owner or his maintenance representative must keep the original of each form at the facility and send a copy to the appropriate FAA regional office at the end of each month in which it is prepared. However, where an FAA approved remote monitoring system is installed which precludes the need for periodic maintenance visits to the facility, monthly reports from the remote monitoring system control point must be forwarded to the appropriate FAA regional office, and a hard copy retained at the control point.
(c) Technical Performance Record (FAA Form 6830 (formerly FAA Form 418)). This form contains a record of system parameters as specified in the manufacturer's equipment manual. This data will be recorded on each scheduled visit to the facility. The owner or his maintenance representative shall keep the original of each record at the facility and send a copy of the form to the appropriate FAA regional office.
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