title-14-part-27-sec27-685

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14 CFR Ch. I (1–1–24 Edition)

§ 27.673

Primary flight control.

Primary flight controls are those

used by the pilot for immediate control
of pitch, roll, yaw, and vertical motion
of the rotorcraft.

[Amdt. 27–21, 49 FR 44434, Nov. 6, 1984]

§ 27.674

Interconnected controls.

Each primary flight control system

must provide for safe flight and landing
and operate independently after a mal-
function, failure, or jam of any auxil-
iary interconnected control.

[Amdt. 27–26, 55 FR 8001, Mar. 6, 1990]

§ 27.675

Stops.

(a) Each control system must have

stops that positively limit the range of
motion of the pilot’s controls.

(b) Each stop must be located in the

system so that the range of travel of
its control is not appreciably affected
by—

(1) Wear;
(2) Slackness; or
(3) Takeup adjustments.
(c) Each stop must be able to with-

stand the loads corresponding to the
design conditions for the system.

(d) For each main rotor blade—
(1) Stops that are appropriate to the

blade design must be provided to limit
travel of the blade about its hinge
points; and

(2) There must be means to keep the

blade from hitting the droop stops dur-
ing any operation other than starting
and stopping the rotor.

(Secs. 313(a), 601, 603, 604, Federal Aviation
Act of 1958 (49 U.S.C. 1354(a), 1421, 1423, 1424),
sec. 6(c), Dept. of Transportation Act (49
U.S.C. 1655(c)))

[Doc. No. 5074, 29 FR 15695, Nov. 24, 1964, as
amended by Amdt. 27–16, 43 FR 50599, Oct. 30,
1978]

§ 27.679

Control system locks.

If there is a device to lock the con-

trol system with the rotorcraft on the
ground or water, there must be means
to—

(a) Give unmistakable warning to the

pilot when the lock is engaged; and

(b) Prevent the lock from engaging in

flight.

§ 27.681

Limit load static tests.

(a) Compliance with the limit load

requirements of this part must be
shown by tests in which—

(1) The direction of the test loads

produces the most severe loading in the
control system; and

(2) Each fitting, pulley, and bracket

used in attaching the system to the
main structure is included.

(b) Compliance must be shown (by

analyses or individual load tests) with
the special factor requirements for
control system joints subject to angu-
lar motion.

§ 27.683

Operation tests.

It must be shown by operation tests

that, when the controls are operated
from the pilot compartment with the
control system loaded to correspond
with loads specified for the system, the
system is free from—

(a) Jamming;
(b) Excessive friction; and
(c) Excessive deflection.

§ 27.685

Control system details.

(a) Each detail of each control sys-

tem must be designed to prevent jam-
ming, chafing, and interference from
cargo, passengers, loose objects or the
freezing of moisture.

(b) There must be means in the cock-

pit to prevent the entry of foreign ob-
jects into places where they would jam
the system.

the slapping of cables or tubes against
other parts.

(d) Cable systems must be designed

as follows:

(1) Cables, cable fittings, turn-

buckles, splices, and pulleys must be of
an acceptable kind.

(2) The design of the cable systems

must prevent any hazardous change in
cable tension throughout the range of
travel under any operating conditions
and temperature variations.

(3) No cable smaller than three thir-

ty-seconds of an inch diameter may be
used in any primary control system.

(4) Pulley kinds and sizes must cor-

respond to the cables with which they
are used. The pulley cable combina-
tions and strength values which must
be used are specified in Military Hand-
book MIL-HDBK-5C, Vol. 1 & Vol. 2,

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Federal Aviation Administration, DOT

§ 27.725

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, Pennsyl-
vania, 19120. Copies may be inspected
at the National Archives and Records
Administration (NARA). For informa-
tion on the availability of this mate-
rial at NARA, call 202–741–6030, or go
to:

http://www.archives.gov/federal-reg-

ister/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 3

(8) No clevis pin subject to load or

motion and retained only by cotter
pins may be used in the control sys-
tem.

(9) Turnbuckles attached to parts

having angular motion must be in-
stalled to prevent binding throughout
the range of travel.

(10) There must be means for visual

inspection at each fairlead, pulley, ter-
minal, 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 rat-
ing of ball and roller bearings must not
be exceeded.

[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]

§ 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.

§ 27.691

Autorotation control mecha-

nism.

Each main rotor blade pitch control

mechanism must allow rapid entry into
autorotation after power failure.

§ 27.695

Power boost and power-oper-

ated control system.

(a) If a power boost or power-oper-

ated control system is used, an alter-
nate 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 actu-
ators.

(such as piston rods and links), and the
jamming of power cylinders, must be
considered unless they are extremely
improbable.

ANDING

EAR

§ 27.723

Shock absorption tests.

The landing inertia load factor and

the reserve energy absorption capacity
of the landing gear must be substan-
tiated by the tests prescribed in
§§ 27.725 and 27.727, respectively. These
tests must be conducted on the com-
plete rotorcraft or on units consisting
of wheel, tire, and shock absorber in
their proper relation.

§ 27.725

Limit drop test.

The limit drop test must be con-

ducted 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 con-
tact velocity equal to the greatest
probable sinking speed likely to occur