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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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