COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 737 Series Aeroplanes AD/B737/63 Stabilizer Trim Jackscrew Actuator 12/91 Applicability: Model 737-300, -400 and -500 series, as listed in Boeing SB 737-27-1161. Requirement: Action in accordance with the Technical Requirements of FAA AD 91-20-04 Amdt 39-8038. Note: Boeing SB 737-27-1161 refers. Compliance: As specified in the requirement document with a revised effective date of 12 December 1991 for Australian registered aircraft. Background: Reports have been received of worn auxiliary trim brakes that may allow slippage and movement of the horizontal stabilizer under certain conditions. The effective date required by the FAA is extended by one month.