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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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271 

Federal Aviation Administration, DOT 

§ 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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