Section 27.687

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

Metallic Materials and Elements for
Flight Vehicle Structures, (Sept. 15,
1976, as amended through December 15,
1978). This incorporation by reference
was approved by the Director of the
Federal Register in accordance with 5
U.S.C. section 552(a) and 1 CFR part 51.
Copies may be obtained from the Naval
Publications and Forms Center, 5801
Tabor Avenue, Philadelphia, Pennsylvania, 19120. Copies may be inspected
at the National Archives and Records
Administration (NARA). For information on the availability of this material at NARA, call 202-741-6030, or go
to:
http://www.archives.gov/federal-register/cfr/ibr-locations.html
(5) Pulleys must have close fitting
guards to prevent the cables from being
displaced or fouled.
(6) Pulleys must lie close enough to
the plane passing through the cable to
prevent the cable from rubbing against
the pulley flange.
(7) No fairlead may cause a change in
cable direction of more than 3Section.
(8) No clevis pin subject to load or
motion and retained only by cotter
pins may be used in the control system.
(9) Turnbuckles attached to parts
having angular motion must be installed to prevent binding throughout
the range of travel.
(10) There must be means for visual
inspection at each fairlead, pulley, terminal, and turnbuckle.
(e) Control system joints subject to
angular motion must incorporate the
following special factors with respect
to the ultimate bearing strength of the
softest material used as a bearing:
(1) 3.33 for push-pull systems other
than ball and roller bearing systems.
(2) 2.0 for cable systems.
(f) For control system joints, the
manufacturer-s static, non-Brinell rating of ball and roller bearings must not
be exceeded.

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; Amdt. 27-26, 55 FR 8001, Mar. 6, 1990; 69
FR 18803, Apr. 9, 2004; Doc. No. FAA-2018-
0119, Amdt. 27-49, 83 FR 9170, Mar. 5, 2018]

Section 27.687

Spring devices.

(a) Each control system spring device
whose failure could cause flutter or

other unsafe characteristics must be
reliable.
(b) Compliance with paragraph (a) of
this section must be shown by tests
simulating service conditions.
Section 27.691 Autorotation control mechanism.
Each main rotor blade pitch control
mechanism must allow rapid entry into
autorotation after power failure.
Section 27.695 Power boost and power-operated control system.
(a) If a power boost or power-operated control system is used, an alternate system must be immediately
available that allows continued safe
flight and landing in the event of - 
(1) Any single failure in the power
portion of the system; or
(2) The failure of all engines.
(b) Each alternate system may be a
duplicate power portion or a manually
operated mechanical system. The
power portion includes the power
source (such as hydraulic pumps), and
such items as valves, lines, and actuators.
(c) The failure of mechanical parts
(such as piston rods and links), and the
jamming of power cylinders, must be
considered unless they are extremely
improbable.
LANDING GEAR
Section 27.723

Shock absorption tests.

The landing inertia load factor and
the reserve energy absorption capacity
of the landing gear must be substantiated by the tests prescribed in
SectionSection 27.725 and 27.727, respectively. These
tests must be conducted on the complete rotorcraft or on units consisting
of wheel, tire, and shock absorber in
their proper relation.
Section 27.725

Limit drop test.

The limit drop test must be conducted as follows:
(a) The drop height must be - 
(1) 13 inches from the lowest point of
the landing gear to the ground; or
(2) Any lesser height, not less than
eight inches, resulting in a drop contact velocity equal to the greatest
probable sinking speed likely to occur

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