COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 727 Series Aeroplanes AD/B727/153 Main Landing Gear Manual Extension Gearbox 6/98 Applicability: All Model 727 series aircraft. Requirement: Inspect in accordance with the technical requirements of FAA AD 98-04-29 Amdt 39- 10341. Note: Boeing Service Bulletin 727-32-279 refers. Compliance: Before 21 November 1998 for the initial inspection and thereafter in accordance with FAA AD 98-04-29 Amdt 39-10341. This airworthiness directive becomes effective on 21 May 1998. Background: The FAA received a report indicating that a manual gearbox assembly which contained an incorrect housing, was installed on a Model 727 series aircraft. Incorrect housings are manufactured from 7079-T6 aluminium and may fail as a result of stress corrosion cracking, and ultimately result in an inability to lock the main landing gear in a down position during landing.