14 CFR § 27.939 - Turbine engine operating characteristics.
---
identifier: "/us/cfr/t14/s27.939"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "14 CFR § 27.939 - Turbine engine operating characteristics."
title_number: 14
title_name: "Aeronautics and Space"
section_number: "27.939"
section_name: "Turbine engine operating characteristics."
chapter_name: "FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION"
subchapter_number: "C"
subchapter_name: "AIRCRAFT"
part_number: "27"
part_name: "AIRWORTHINESS STANDARDS: NORMAL CATEGORY ROTORCRAFT"
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, 44704."
regulatory_source: "Docket No. 5074, 29 FR 15695, Nov. 24, 1964, unless otherwise noted."
cfr_part: "27"
---
# 27.939 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 rotorcraft and of the engine.
(b) The turbine engine air inlet system may not, as a result of airflow distortion during normal operation, cause vibration harmful to the engine.
(c) For governor-controlled engines, it must be shown that there exists no hazardous torsional instability of the drive system associated with critical combinations of power, rotational speed, and control displacement.
[Amdt. 27-1, 32 FR 6914, May 5, 1967, as amended by Amdt. 27-11, 41 FR 55469, Dec. 20, 1976]