AD/INST/12 SEP 6 Automatic Pilot Roll Computer Clutch Circuit Modification Cancelled (Cth)

AIRWORTHINESS DIRECTIVE

On the effective date specified below, and for the reasons set out in the background section, the CASA delegate whose signature appears below revokes Airworthiness Directive AD/INST/12.

Instruments and Automatic Pilots

AD/INST/12 SEP 6 Automatic Pilot Roll Computer
Clutch Circuit - Modification 3/2009

Requirement:

CANCELLED.

This AD is cancelled on 12 March 2009.

Background:

This unique Australian AD raised in 1975 against Smiths Industries Ltd Service Bulletin (SB) SB 22-778 which recommended that a modification to the existing design of the roll computer clutch circuit be accomplished as it had been found that it was possible for the autopilot to inadvertently disengage, then re-engage.

Compliance was within 3000 hours TIS after 30 April 1975.

At the time the AD was raised, no defects described in the SB had been reported in Australia, and none since.  Also, Smith Industries (Aust) stated that the possibility of such a defect occurring was unlikely.  For this reason, the compliance period was arrived at to allow for adequate time for industry to program the modification of the applicable units during routine maintenance.

Given the foregoing, and the extended time this AD has been promulgated it is considered that the clutch circuits of the affected roll computers would have been modified by now, therefore this AD is considered to be no longer required.

James Coyne
Delegate of the Civil Aviation Safety Authority

27 January 2009