14 C.F.R. § 125.115 Internal doors.
Title 14 - Aeronautics and Space
In any case where internal doors are equipped with louvres or other ventilating means, there must be a means convenient to the crew for closing the flow of air through the door when necessary.
Title 14: Aeronautics and Space
PART 125—CERTIFICATION AND OPERATIONS: AIRPLANES HAVING A SEATING CAPACITY OF 20 OR MORE PASSENGERS OR A MAXIMUM PAYLOAD CAPACITY OF 6,000 POUNDS OR MORE; AND RULES GOVERNING PERSONS ON BOARD SUCH AIRCRAFT
Subpart E—Special Airworthiness Requirements
§ 125.115 Internal doors.