{"id":"F2006B02990","name":"AD/B737/9 - Horizontal Stabilizer - Centre Section Rear Spar","slug":"ad-b737-9-horizontal-stabilizer-centre-section-rear-spar","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42349,"registerId":"commonwealth-F2006B02990-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B737/9 - Horizontal Stabilizer - Centre Section Rear Spar","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nBoeing 737 Series Aeroplanes\n\nAD/B737/9 Horizontal Stabilizer \\- Centre Section Rear Spar 9/86\n\nApplicability: Line numbers 209 and on, except 737-300 models. Requirement: Inspect in accordance with Boeing SB No. 737-55-1034.\n\nNote: FAA AD 86-12-04 refers.\n\nCompliance: (a) Before exceeding 50,000 landings; or\n\n    (b) Before exceeding 50,000 landings after chord replacement; or\n\n    (c) Before exceeding 35,000 landings after modification in accordance with Part II of the Requirement Document; or\n\n    (d) Before exceeding 9,000 landings after repair in accordance with Part ;II of the Requirement Document; or\n\n    (e) Within 500 landings after 30 September 1986;\n\nwhichever is the latest, and thereafter at intervals not exceeding 4,500 landings.\n\nBackground: 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.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted airworthiness directive focused on a specific structural inspection for a defined aircraft population. It has not expanded beyond its original safety purpose."},"complexity_factors":["Multiple alternative compliance deadlines (5 different triggering conditions in sub-paragraphs a-e)","Cross-reference to external technical document (Boeing Service Bulletin 737-55-1034) without reproducing its contents","Reference to US FAA directive (FAA AD 86-12-04) for additional context","Technical aviation terminology requiring specialized knowledge (horizontal stabilizer, rear spar, upper chord, gusset plates, tapered shank fasteners)","Conditional logic ('whichever is the latest') determining actual compliance date","Ongoing recurring obligation ('thereafter at intervals not exceeding 4,500 landings')"],"plain_english_summary":"This AD requires operators of Boeing 737s (line numbers 209 and higher; excludes 737-300) to inspect the horizontal stabilizer centre-section rear spar per Boeing Service Bulletin 737-55-1034. \n\nIt's a preventive safety measure prompted by earlier cracking on older 737s. Inspection timing depends on landing counts and component history, with repeat checks every 4,500 landings."},"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":true,"description":"The directive applies precautionary inspections to later‑production Boeing 737s (line numbers 209 and on, excluding 737‑300) even though the documented cracking history concerned earlier production aircraft (lines 1–208). This extends inspection obligations beyond the set of aircraft where cracks were reported (Applicability; Background)."},"complexity_factors":["Multiple conditional compliance triggers tied to different events and landing counts (Compliance (a)–(e)).","Recurring inspection interval requirement after initial compliance (every 4,500 landings) (Compliance).","Mandates work to an external normative document (Boeing Service Bulletin No. 737‑55‑1034) rather than setting detailed procedures in the AD (Requirement).","Applicability is limited and model‑specific (line numbers 209 and on; excludes 737‑300), requiring operators to determine line number applicability (Applicability).","Contrast between technical history and scope: earlier production (lines 1–208) had cracking, later production shows no reported cracks but is still subject to precautionary inspections (Background).","Cross‑reference to FAA AD (Note), adding another external regulatory source for interpretive context."],"plain_english_summary":"Requires operators of Boeing 737s (line numbers 209 and later, excluding 737‑300s) to carry out inspections of the horizontal stabilizer centre‑section rear spar following Boeing SB 737‑55‑1034. Inspections must occur at specified landing‑count triggers (Compliance (a)–(e)) and then every 4,500 landings. The measure is a precautionary check though previous cracking was reported on earlier‑production aircraft (Background)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-9-horizontal-stabilizer-centre-section-rear-spar","history":"/api/acts/ad-b737-9-horizontal-stabilizer-centre-section-rear-spar/history","analysis":"/api/acts/ad-b737-9-horizontal-stabilizer-centre-section-rear-spar/analysis","conflicts":"/api/acts/ad-b737-9-horizontal-stabilizer-centre-section-rear-spar/conflicts","importantCases":"/api/acts/ad-b737-9-horizontal-stabilizer-centre-section-rear-spar/important-cases","documents":"/api/acts/ad-b737-9-horizontal-stabilizer-centre-section-rear-spar/documents"}}