270
14 CFR Ch. I (1–1–24 Edition)
§ 25.683
(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.
§ 25.683
Operation tests.
(a) It must be shown by operation
tests that when portions of the control
system subject to pilot effort loads are
loaded to 80 percent of the limit load
specified for the system and the pow-
ered portions of the control system are
loaded to the maximum load expected
in normal operation, the system is free
from—
(1) Jamming;
(2) Excessive friction; and
(3) Excessive deflection.
(b) It must be shown by analysis and,
where necessary, by tests, that in the
presence of deflections of the airplane
structure due to the separate applica-
tion of pitch, roll, and yaw limit ma-
neuver loads, the control system, when
loaded to obtain these limit loads and
operated within its operational range
of deflections, can be exercised about
all control axes and remain free from—
(1) Jamming;
(2) Excessive friction;
(3) Disconnection; and
(4) Any form of permanent damage.
(c) It must be shown that under vi-
bration loads in the normal flight and
ground operating conditions, no hazard
can result from interference or contact
with adjacent elements.
[Amdt. 25–139, 79 FR 59430, Oct. 2, 2014]
§ 25.685
Control system details.
(a) Each detail of each control sys-
tem must be designed and installed to
prevent jamming, chafing, and inter-
ference 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.
(c) There must be means to prevent
the slapping of cables or tubes against
other parts.
(d) Sections 25.689 and 25.693 apply to
cable systems and joints.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as
amended by Amdt. 25–38, 41 FR 55466, Dec. 20,
1976]
§ 25.689
Cable systems.
(a) Each cable, cable fitting, turn-
buckle, splice, and pulley must be ap-
proved. In addition—
(1) No cable smaller than
1
⁄
8
inch in
diameter may be used in the aileron,
elevator, or rudder systems; and
(2) Each cable system must be de-
signed so that there will be no haz-
ardous change in cable tension
throughout the range of travel under
operating conditions and temperature
variations.
(b) Each kind and size of pulley must
correspond to the cable with which it is
used. Pulleys and sprockets must have
closely fitted guards to prevent the ca-
bles and chains from being displaced or
fouled. Each pulley must lie in the
plane passing through the cable so that
the cable does not rub against the pul-
ley flange.
(c) Fairleads must be installed so
that they do not cause a change in
cable direction of more than three de-
grees.
(d) Clevis pins subject to load or mo-
tion and retained only by cotter pins
may not be used in the control system.
(e) Turnbuckles must be attached to
parts having angular motion in a man-
ner that will positively prevent binding
throughout the range of travel.
(f) There must be provisions for vis-
ual inspection of fairleads, pulleys, ter-
minals, and turnbuckles.
§ 25.693
Joints.
Control system joints (in push-pull
systems) that are subject to angular
motion, except those in ball and roller
bearing systems, must have a special
factor of safety of not less than 3.33
with respect to the ultimate bearing
strength of the softest material used as
a bearing. This factor may be reduced
to 2.0 for joints in cable control sys-
tems. For ball or roller bearings, the
approved ratings may not be exceeded.
[Amdt. 25–72, 55 FR 29777, July 20, 1990]
§ 25.697
Lift and drag devices, con-
trols.
(a) Each lift device control must be
designed so that the pilots can place
the device in any takeoff, en route, ap-
proach, or landing position established
under § 25.101(d). Lift and drag devices
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§ 25.703
must maintain the selected positions,
except for movement produced by an
automatic positioning or load limiting
device, without further attention by
the pilots.
(b) Each lift and drag device control
must be designed and located to make
inadvertent operation improbable. Lift
and drag devices intended for ground
operation only must have means to
prevent the inadvertant operation of
their controls in flight if that oper-
ation could be hazardous.
(c) The rate of motion of the surfaces
in response to the operation of the con-
trol and the characteristics of the
automatic positioning or load limiting
device must give satisfactory flight
and performance characteristics under
steady or changing conditions of air-
speed, engine power, and airplane atti-
tude.
(d) The lift device control must be
designed to retract the surfaces from
the fully extended position, during
steady flight at maximum continuous
engine power at any speed below
V
F
+
9.0 (knots).
[Amdt. 25–23, 35 FR 5675, Apr. 8, 1970, as
amended by Amdt. 25–46, 43 FR 50595, Oct. 30,
1978; Amdt. 25–57, 49 FR 6848, Feb. 23, 1984]
§ 25.699
Lift and drag device indicator.
(a) There must be means to indicate
to the pilots the position of each lift or
drag device having a separate control
in the cockpit to adjust its position. In
addition, an indication of unsymmet-
rical operation or other malfunction in
the lift or drag device systems must be
provided when such indication is nec-
essary to enable the pilots to prevent
or counteract an unsafe flight or
ground condition, considering the ef-
fects on flight characteristics and per-
formance.
(b) There must be means to indicate
to the pilots the takeoff, en route, ap-
proach, and landing lift device posi-
tions.
(c) If any extension of the lift and
drag devices beyond the landing posi-
tion is possible, the controls must be
clearly marked to identify this range
of extension.
[Amdt. 25–23, 35 FR 5675, Apr. 8, 1970]
§ 25.701
Flap and slat interconnection.
(a) Unless the airplane has safe flight
characteristics with the flaps or slats
retracted on one side and extended on
the other, the motion of flaps or slats
on opposite sides of the plane of sym-
metry must be synchronized by a me-
chanical interconnection or approved
equivalent means.
(b) If a wing flap or slat interconnec-
tion or equivalent means is used, it
must be designed to account for the ap-
plicable unsymmetrical loads, includ-
ing those resulting from flight with the
engines on one side of the plane of sym-
metry inoperative and the remaining
engines at takeoff power.
(c) For airplanes with flaps or slats
that are not subjected to slipstream
conditions, the structure must be de-
signed for the loads imposed when the
wing flaps or slats on one side are car-
rying the most severe load occurring in
the prescribed symmetrical conditions
and those on the other side are car-
rying not more than 80 percent of that
load.
(d) The interconnection must be de-
signed for the loads resulting when
interconnected flap or slat surfaces on
one side of the plane of symmetry are
jammed and immovable while the sur-
faces on the other side are free to move
and the full power of the surface actu-
ating system is applied.
[Amdt. 25–72, 55 FR 29777, July 20, 1990]
§ 25.703
Takeoff warning system.
A takeoff warning system must be in-
stalled and must meet the following re-
quirements:
(a) The system must provide to the
pilots an aural warning that is auto-
matically activated during the initial
portion of the takeoff roll if the air-
plane is in a configuration, including
any of the following, that would not
allow a safe takeoff:
(1) The wing flaps or leading edge de-
vices are not within the approved range
of takeoff positions.
(2) Wing spoilers (except lateral con-
trol spoilers meeting the requirements
of § 25.671), speed brakes, or longitu-
dinal trim devices are in a position
that would not allow a safe takeoff.
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