626 

14 CFR Ch. I (1–1–24 Edition) 

§ 29.907 

(b) 

Category A; engine isolation. For 

each category A rotorcraft, the power-
plants must be arranged and isolated 
from each other to allow operation, in 
at least one configuration, so that the 
failure or malfunction of any engine, or 
the failure of any system that can af-
fect any engine, will not— 

(1) Prevent the continued safe oper-

ation of the remaining engines; or 

(2) Require immediate action, other 

than normal pilot action with primary 
flight controls, by any crewmember to 
maintain safe operation. 

(c) 

Category A; control of engine rota-

tion.  For each Category A rotorcraft, 
there must be a means for stopping the 
rotation of any engine individually in 
flight, except that, for turbine engine 
installations, the means for stopping 
the engine need be provided only where 
necessary for safety. In addition— 

(1) Each component of the engine 

stopping system that is located on the 
engine side of the firewall, and that 
might be exposed to fire, must be at 
least fire resistant; or 

(2) Duplicate means must be avail-

able for stopping the engine and the 
controls must be where all are not like-
ly to be damaged at the same time in 
case of fire. 

(d) 

Turbine engine installation. For 

turbine engine installations— 

(1) Design precautions must be taken 

to minimize the hazards to the rotor-
craft in the event of an engine rotor 
failure; and 

(2) The powerplant systems associ-

ated with engine control devices, sys-
tems, and instrumentation must be de-
signed to give reasonable assurance 
that those engine operating limitations 
that adversely affect engine rotor 
structural integrity will not be exceed-
ed in service. 

(e) 

Restart capability. (1) A means to 

restart any engine in flight must be 
provided. 

(2) Except for the in-flight shutdown 

of all engines, engine restart capability 
must be demonstrated throughout a 
flight envelope for the rotorcraft. 

(3) Following the in-flight shutdown 

of all engines, in-flight engine restart 
capability must be provided. 

(Secs. 313(a), 601, and 603, 72 Stat. 752, 775, 49 
U.S.C. 1354(a), 1421, and 1423; sec. 6(c), 49 
U.S.C. 1655(c)) 

[Doc. No. 5084, 29 FR 16150, Dec. 3, 1964, as 
amended by Amdt. 29–12, 41 FR 55472, Dec. 20, 
1976; Amdt. 29–26, 53 FR 34215, Sept. 2, 1988; 
Amdt. 29–31, 55 FR 38967, Sept. 21, 1990; 55 FR 
41309, Oct. 10, 1990; Amdt. 29–36, 60 FR 55776, 
Nov. 2, 1995] 

§ 29.907

Engine vibration. 

(a) Each engine must be installed to 

prevent the harmful vibration of any 
part of the engine or rotorcraft. 

(b) The addition of the rotor and the 

rotor drive system to the engine may 
not subject the principal rotating parts 
of the engine to excessive vibration 
stresses. This must be shown by a vi-
bration investigation. 

§ 29.908

Cooling fans. 

For cooling fans that are a part of a 

powerplant installation the following 
apply: 

(a) 

Category A. For cooling fans in-

stalled in Category A rotorcraft, it 
must be shown that a fan blade failure 
will not prevent continued safe flight 
either because of damage caused by the 
failed blade or loss of cooling air. 

(b) 

Category B. For cooling fans in-

stalled in category B rotorcraft, there 
must be means to protect the rotor-
craft and allow a safe landing if a fan 
blade fails. It must be shown that— 

(1) The fan blade would be contained 

in the case of a failure; 

(2) Each fan is located so that a fan 

blade failure will not jeopardize safety; 
or 

(3) Each fan blade can withstand an 

ultimate load of 1.5 times the cen-
trifugal force expected in service, lim-
ited by either— 

(i) The highest rotational speeds 

achievable under uncontrolled condi-
tions; or 

(ii) An overspeed limiting device. 
(c) 

Fatigue evaluation. Unless a fa-

tigue evaluation under § 29.571 is con-
ducted, it must be shown that cooling 

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