Section 27.907

14 CFR Ch. I (1-1-19 Edition)

(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. 27-44, 73 FR 11000, Feb. 29, 2008]

Section 27.907 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 vibration investigation.
(c) No part of the rotor drive system
may be subjected to excessive vibration stresses.
ROTOR DRIVE SYSTEM
Section 27.917 Design.
(a) Each rotor drive system must incorporate a unit for each engine to
automatically disengage that engine
from the main and auxiliary rotors if
that engine fails.
(b) Each rotor drive system must be
arranged so that each rotor necessary
for control in autorotation will continue to be driven by the main rotors
after disengagement of the engine from
the main and auxiliary rotors.
(c) If a torque limiting device is used
in the rotor drive system, it must be
located so as to allow continued control of the rotorcraft when the device
is operating.
(d) The rotor drive system includes
any part necessary to transmit power
from the engines to the rotor hubs.
This includes gear boxes, shafting, universal joints, couplings, rotor brake assemblies, clutches, supporting bearings
for shafting, any attendant accessory
pads or drives, and any cooling fans
that are a part of, attached to, or
mounted on the rotor drive system.

spaschal on DSK3GDR082PROD with CFR

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27-11, 41 FR 55469, Dec. 20,
1976]

Section 27.921 Rotor brake.
If there is a means to control the rotation of the rotor drive system independently 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 inadvertent operation.
Section 27.923 Rotor drive system and control mechanism tests.
(a) Each part tested as prescribed in
this section must be in a serviceable
condition at the end of the tests. No intervening disassembly which might affect test results may be conducted.
(b) Each rotor drive system and control mechanism must be tested for not
less than 100 hours. The test must be
conducted on the rotorcraft, and the
torque must be absorbed by the rotors
to be installed, except that other
ground or flight test facilities with
other appropriate methods of torque
absorption may be used if the conditions of support and vibration closely
simulate the conditions that would
exist during a test on the rotorcraft.
(c) A 60-hour part of the test prescribed in paragraph (b) of this section
must be run at not less than maximum
continuous torque and the maximum
speed for use with maximum continuous torque. In this test, the main
rotor controls must be set in the position that will give maximum longitudinal cyclic pitch change to simulate
forward flight. The auxiliary rotor controls must be in the position for normal operation under the conditions of
the test.
(d) A 30-hour or, for rotorcraft for
which the use of either 30-minute OEI
power or continuous OEI power is requested, a 25-hour part of the test prescribed in paragraph (b) of this section
must be run at not less than 75 percent
of maximum continuous torque and the
minimum speed for use with 75 percent
of maximum continuous torque. The
main and auxiliary rotor controls must
be in the position for normal operation
under the conditions of the test.
(e) A 10-hour part of the test prescribed in paragraph (b) of this section
must be run at not less than takeoff
torque and the maximum speed for use
with takeoff torque. The main and auxiliary rotor controls must be in the
normal position for vertical ascent.
(1) For multiengine rotorcraft for
which the use of 21-2 minute OEI power

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