COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY SCHEDULE OF AIRWORTHINESS DIRECTIVES Boeing 737 Series Aeroplanes AD/B737/9 Horizontal Stabilizer - Centre Section Rear Spar 9/86 Applicability: Line numbers 209 and on, except 737-300 models. Requirement: Inspect in accordance with Boeing SB No. 737-55-1034. Note: FAA AD 86-12-04 refers. Compliance: (a) Before exceeding 50,000 landings; or (b) Before exceeding 50,000 landings after chord replacement; or (c) Before exceeding 35,000 landings after modification in accordance with Part II of the Requirement Document; or (d) Before exceeding 9,000 landings after repair in accordance with Part ;II of the Requirement Document; or (e) Within 500 landings after 30 September 1986; whichever is the latest, and thereafter at intervals not exceeding 4,500 landings. Background: Earlier production 737 aircraft, ie line numbers 1 to 208, had a history of cracking in the rear spar upper chord at the gusset plates. Although later production aircraft have tapered shank fasteners at these locations, and no cracks have been reported to date, it is felt that the structural significance of this area warrants precautionary inspections to ensure flight safety.