title-14-part-29-sec29-908

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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§ 29.923

fan blades are not operating at reso-
nant conditions within the operating
limits of the rotorcraft.

(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))

[Amdt. 29–13, 42 FR 15046, Mar. 17, 1977, as
amended by Amdt. 29–26, 53 FR 34215, Sept. 2,
1988]

OTOR

RIVE

YSTEM

§ 29.917

Design.

(a)

General. The rotor drive system

includes any part necessary to trans-
mit power from the engines to the
rotor hubs. This includes gear boxes,
shafting, universal joints, couplings,
rotor brake assemblies, clutches, sup-
porting bearings for shafting, any at-
tendant accessory pads or drives, and
any cooling fans that are a part of, at-
tached to, or mounted on the rotor
drive system.

(b)

Design assessment. A design assess-

ment must be performed to ensure that
the rotor drive system functions safely
over the full range of conditions for
which certification is sought. The de-
sign assessment must include a de-
tailed failure analysis to identify all
failures that will prevent continued
safe flight or safe landing and must
identify the means to minimize the
likelihood of their occurrence.

(c)

Arrangement. Rotor drive systems

must be arranged as follows:

(1) Each rotor drive system of multi-

engine rotorcraft must be arranged so
that each rotor necessary for operation
and control will continue to be driven
by the remaining engines if any engine
fails.

(2) For single-engine rotorcraft, each

rotor drive system must be so arranged
that each rotor necessary for control in
autorotation will continue to be driven
by the main rotors after disengage-
ment of the engine from the main and
auxiliary rotors.

(3) Each rotor drive system must in-

corporate a unit for each engine to
automatically disengage that engine
from the main and auxiliary rotors if
that engine fails.

(4) If a torque limiting device is used

in the rotor drive system, it must be
located so as to allow continued con-

trol of the rotorcraft when the device
is operating.

(5) If the rotors must be phased for

intermeshing, each system must pro-
vide constant and positive phase rela-
tionship under any operating condi-
tion.

(6) If a rotor dephasing device is in-

corporated, there must be means to
keep the rotors locked in proper phase
before operation.

[Doc. No. 5084, 29 FR 16150, Dec. 3, 1964, as
amended by Amdt. 29–12, 41 FR 55472, Dec. 20,
1976; Amdt. 29–40, 61 FR 21908, May 10, 1996]

§ 29.921

Rotor brake.

If there is a means to control the ro-

tation of the rotor drive system inde-
pendently of the engine, any limita-
tions on the use of that means must be
specified, and the control for that
means must be guarded to prevent in-
advertent operation.

§ 29.923

Rotor drive system and con-

trol mechanism tests.

(a)

Endurance tests, general. Each

rotor drive system and rotor control
mechanism must be tested, as pre-
scribed in paragraphs (b) through (n)
and (p) of this section, for at least 200
hours plus the time required to meet
the requirements of paragraphs (b)(2),
(b)(3), and (k) of this section. These
tests must be conducted as follows:

(1) Ten-hour test cycles must be used,

except that the test cycle must be ex-
tended to include the OEI test of para-
graphs (b)(2) and (k), of this section if
OEI ratings are requested.

(2) The tests must be conducted on

the rotorcraft.

(3) The test torque and rotational

speed must be—

(i) Determined by the powerplant

limitations; and

(ii) Absorbed by the rotors to be ap-

proved for the rotorcraft.

(b)

Endurance tests; takeoff run. The

takeoff run must be conducted as fol-
lows:

(1) Except as prescribed in para-

graphs (b)(2) and (b)(3) of this section,
the takeoff torque run must consist of
1 hour of alternate runs of 5 minutes at
takeoff torque and the maximum speed
for use with takeoff torque, and 5 min-
utes at as low an engine idle speed as