background image


14 CFR Ch. I (1–1–19 Edition) 

§ 29.681 

(a) Automatically disengage the lock 

when the pilot operates the controls in 
a normal manner, or limit the oper-
ation of the rotorcraft so as to give un-
mistakable warning to the pilot before 
takeoff; and 

(b) Prevent the lock from engaging in 


§ 29.681

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. 

§ 29.683

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. 

§ 29.685

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. 

(c) There must be means to prevent 

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 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 



inch di-

ameter 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 specified in 
MIL-HDBK-5 must be used unless they 
are inapplicable. 

(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 three de-

(8) No clevis pin subject to load or 

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

(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 may not 
be exceeded. 

[Doc. No. 5084, 29 FR 16150, Dec. 3, 1964, as 
amended by Amdt. 29–12, 41 FR 55471, Dec. 20, 

§ 29.687

Spring devices. 

(a) Each control system spring device 

whose failure could cause flutter or 
other unsafe characteristics must be 

(b) Compliance with paragraph (a) of 

this section must be shown by tests 
simulating service conditions. 

VerDate Sep<11>2014 

12:50 Apr 30, 2019

Jkt 247046

PO 00000

Frm 00616

Fmt 8010

Sfmt 8010



spaschal on DSK3GDR082PROD with CFR