CS 22.689  Cable systems

CAA ORS9 Decision No. 1

(a) Each cable, cable fitting, turnbuckle, splice, and pulley used must meet approved specifications.

In addition – 

(1) no cable smaller than 3 mm diameter may be used in primary control systems; 

(2) each cable system must be designed so that there will be no hazardous change in cable tension throughout the range of travel under operating conditions and temperature variations; and 

(3) there must be means for visual inspection at each fairlead, pulley, terminal, and turnbuckle. The need for this requirement may be waived when it can be shown that airworthiness will not be affected within the service life of these components. 

(b) Each kind and size of pulley must correspond to the cable with which it is used. Each pulley must have closely fitted guards to prevent the cables from being misplaced or fouled, even when slack. Each pulley must lie in the plane passing through the cable so that the cable does not rub against the pulley flange.

(c) Fairleads must be installed so that they do not cause a change in cable direction of more than 3°, except where tests or experience indicate that a higher value would be satisfactory. The radius of curvature of fairleads must not be smaller than the radius of a pulley for the same cable.

(d) Turnbuckles must be attached to parts having angular motion in a manner that will positively prevent binding throughout the range of travel.

(e) Tab control cables are not part of the primary control system and may be less than 3 mm diameter in sailplanes that are safely controllable with the tabs in the most adverse positions.