(b) Engine or drive system cooling fan blade protection. (1) If an engine or rotor drive system cooling fan is installed, there must be a means to protect the rotorcraft and allow a safe landing if a fan blade fails. This must be shown by showing that—
(i) The fan blades are contained in case of failure;
(ii) Each fan is located so that a failure will not jeopardize safety; or
(iii) Each fan blade can withstand an ultimate load of 1.5 times the centrifugal force resulting from operation limited by the following:
(A) For fans driven directly by the engine—
( 1 ) The terminal engine r.p.m. under uncontrolled conditions; or
( 2 ) An overspeed limiting device.
(B) For fans driven by the rotor drive system, the maximum rotor drive system rotational speed to be expected in service, including transients.
(2) Unless a fatigue evaluation under §27.571 is conducted, it must be shown that cooling fan blades are not operating at resonant conditions within the operating limits of the rotorcraft.
(c) Turbine engine installation. For turbine engine installations, the powerplant systems associated with engine control devices, systems, and instrumentation must be designed to give reasonable assurance that those engine operating limitations that adversely affect turbine rotor structural integrity will not be exceeded in service.
(d) Restart capability: A means to restart any engine in flight must be provided.
(1) Except for the in-flight shutdown of all engines, engine restart capability must be demonstrated throughout a flight envelope for the rotorcraft.
(2) Following the in-flight shutdown of all engines, in-flight engine restart capability must be provided.
[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as amended by Amdt. 27–11, 41 FR 55469, Dec. 20, 1976; Amdt. 27–23, 53 FR 34211, Sept. 2, 1988; Amdt. No. 27–44, 73 FR 11000, Feb. 29, 2008]