14 CFR § 25.939 - Turbine engine operating characteristics.
---
identifier: "/us/cfr/t14/s25.939"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "14 CFR § 25.939 - Turbine engine operating characteristics."
title_number: 14
title_name: "Aeronautics and Space"
section_number: "25.939"
section_name: "Turbine engine operating characteristics."
chapter_name: "FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION"
subchapter_number: "C"
subchapter_name: "AIRCRAFT"
part_number: "25"
part_name: "AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "49 U.S.C. 106(f), 106(g), 40113, 44701, 44702 and 44704; Pub. L. 115-254, 132 Stat 3281 (49 U.S.C. 44903 note)."
regulatory_source: "Docket No. 5066, 29 FR 18291, Dec. 24, 1964, unless otherwise noted."
cfr_part: "25"
---
# 25.939 Turbine engine operating characteristics.
(a) Turbine engine operating characteristics must be investigated in flight to determine that no adverse characteristics (such as stall, surge, or flameout) are present, to a hazardous degree, during normal and emergency operation within the range of operating limitations of the airplane and of the engine.
(b) [Reserved]
(c) The turbine engine air inlet system may not, as a result of air flow distortion during normal operation, cause vibration harmful to the engine.
[Amdt. 25-11, 32 FR 6912, May 5, 1967, as amended by Amdt. 25-40, 42 FR 15043, Mar. 17, 1977]