271 

Federal Aviation Administration, DOT 

§ 25.701 

(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 
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 

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