14 C.F.R. § 23.959 Unusable fuel supply.
Title 14 - Aeronautics and Space
(a) The unusable fuel supply for each tank must be established as not less than that quantity at which the first evidence of malfunctioning occurs under the most adverse fuel feed condition occurring under each intended operation and flight maneuver involving that tank. Fuel system component failures need not be considered. (b) The effect on the usable fuel quantity as a result of a failure of any pump shall be determined. [Amdt. 23–7, 34 FR 13093, Aug. 13, 1969, as amended by Amdt. 23–18, 42 FR 15041, Mar. 17, 1977; Amdt. 23–51, 61 FR 5136, Feb. 9, 1996]
Title 14: Aeronautics and Space
PART 23—AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES
Subpart E—Powerplant
Fuel System
§ 23.959 Unusable fuel supply.
