---
kind: "section"
citation: "14 C.F.R. § 29.685"
title: "14"
number: "29.685"
heading: "Control system details."
url: "https://uscodex.org/cfr/14/29.685"
---

# §29.685. Control system details.

- (a) Each detail of each control system must be designed to prevent jamming, chafing, and interference from cargo, passengers, loose objects, or the freezing of moisture.
- (b) There must be means in the cockpit to prevent the entry of foreign objects 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, turnbuckles, 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 1/8 inch diameter may be used in any primary control system.
  - (4) Pulley kinds and sizes must correspond to the cables with which they are used. The pulley-cable combinations 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 degrees.
  - (8) No clevis pin subject to load or motion and retained only by cotter pins may be used in the control system.
  - (9) Turnbuckles attached to parts having angular motion must be installed to prevent binding throughout the range of travel.
  - (10) There must be means for visual inspection at each fairlead, pulley, terminal, 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 rating of ball and roller bearings may not be exceeded.

## Notes

### Amendments

[Doc. No. 5084, 29 FR 16150, Dec. 3, 1964, as amended by Amdt. 29-12, 41 FR 55471, Dec. 20, 1976]

### Authority

Authority: 49 U.S.C. 106(f), 106(g), 40113, 44701-44702, 44704.

### Source

Source: Docket No. 5084, 29 FR 16150, Dec. 3, 1964, unless otherwise noted.

### Amendments

[Doc. No. 5084, 29 FR 16150, Dec. 3, 1964, as amended by Amdt. 29-12, 41 FR 55471, Dec. 20, 1976]