{"id":"F2006B02814","name":"AD/B737/11 - Horizontal Stabilizer Centre Section - Rear Spar Upper Chord Attach Lugs","slug":"ad-b737-11-horizontal-stabilizer-centre-section-rear-spar-upper-chord-attach-lugs","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":42156,"registerId":"commonwealth-F2006B02814-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/B737/11 - Horizontal Stabilizer Centre Section - Rear Spar Upper Chord Attach Lugs","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/B737/11 Horizontal Stabilizer Centre Section \\- Rear\n\nSpar Upper Chord Attach Lugs\n\n  \n10/86\n\nApplicability: All 737-100, \\-200 and \\-200C models with Line Numbers 316 to 322, and 325 and subsequent.\n\nRequirement: Inspect in accordance with the Flight Safety Inspection Program specified in Boeing S.B. 737-55-1033.\n\nNote: FAA AD 86-12-05 refers.\n\nCompliance: (a) Before exceeding 40,000 landings; or\n\n(b) Before exceeding 40,000 landings after a chord replacement or modification in accordance with Option 1 of the Requirement Document,\n\nwhichever is the later, and thereafter at intervals not exceeding 5,700 landings.\n\nBackground: Cracks in the lugs, if undetected, could lead to loss of the horizontal stabilizer.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, targeted airworthiness directive addressing a specific structural defect in specific aircraft models. It has not expanded beyond its original purpose of mandating inspections for cracked attach lugs."},"complexity_factors":["Single, specific mechanical component addressed (rear spar upper chord attach lugs)","Limited applicability (specific Boeing 737 models with defined line numbers only)","Straightforward compliance timeline based on landing counts (40,000 initial, 5,700 recurring)","Single reference document (Boeing S.B. 737-55-1033) for inspection procedures","No nested exceptions or conditional logic beyond the 'whichever is later' clause","Minimal defined terms (only standard aviation terminology like 'landings' and 'line numbers')","Short document (approximately 150 words excluding header)"],"plain_english_summary":"This is an **Airworthiness Directive** (a mandatory safety order) issued by Australia's Civil Aviation Safety Authority for specific Boeing 737 aircraft.\n\n**What it does:**\n- Requires owners/operators of certain older Boeing 737 models (-100, -200, and -200C) to inspect a critical structural component called the \"rear spar upper chord attach lugs\" on the horizontal stabilizer (the tail wing that controls the plane's pitch).\n\n**Who it affects:**\n- All Boeing 737-100, -200, and -200C aircraft with specific production line numbers (316-322 and 325 onwards).\n\n**What must be done:**\n- A detailed inspection must be carried out following Boeing's official safety bulletin (S.B. 737-55-1033).\n- **When:** Before the aircraft reaches 40,000 landings, or within 40,000 landings after certain repairs, whichever comes later.\n- **Ongoing:** Repeat the inspection every 5,700 landings after that.\n\n**Why it matters:**\nCracks in these metal lugs (attachment points) could cause the horizontal stabilizer to fail completely, potentially leading to loss of control of the aircraft. This directive prevents catastrophic failure by catching cracks early.\n\n**Note:** This aligns with a similar US Federal Aviation Administration directive (FAA AD 86-12-05)."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive sets a targeted inspection requirement for specific 737-100/200 series aircraft by line number and prescribes inspection intervals tied to landing counts and certain repair events. The prescription and the affected fleet are defined within the instrument itself (Applicability; Requirement; Compliance). There is no indication in the text that the directive expands or narrows that scope from a prior intent; it instead specifies who must inspect, how, and when, without altering applicability within the document."},"complexity_factors":["External technical dependence: The inspection procedure is specified in a Boeing service bulletin rather than fully described in the directive (Requirement).","Quantitative compliance metric: Compliance is tied to landing counts (initial at 40,000 landings and repeat every 5,700 landings), which requires accurate operational tracking (Compliance).","Triggering event nuance: A chord replacement or modification under Option 1 creates an alternate timing trigger for the initial inspection (Compliance (b)).","Narrow applicability by production line number: The directive applies only to particular line numbers of certain 737 models, requiring operators to check serial/line records (Applicability).","Regulatory enforcement: The directive is issued under the Civil Aviation Regulations framework, so non-compliance carries regulatory consequences (header)."],"plain_english_summary":"What this directive does\n\n- Requires specific Boeing 737 aeroplanes to be inspected for cracks in the rear spar upper chord attach lugs of the horizontal stabilizer centre section. (Applicability; Requirement)\n\nWhich aeroplanes are affected\n\n- All Boeing 737-100, -200 and -200C models with line numbers 316 to 322, and 325 and subsequent. (Applicability)\n\nWhat operators must do, mechanically\n\n- Perform the inspection steps set out in Boeing Service Bulletin 737-55-1033 (referred to in the directive as the Flight Safety Inspection Program). (Requirement)\n- Carry out the initial inspection before the aeroplane exceeds 40,000 landings, or before it exceeds 40,000 landings following a chord replacement or modification done under Option 1 of the Requirement Document — whichever of those two is later. After that, repeat the inspection at intervals not greater than 5,700 landings. (Compliance)\n\nWho decides and who pays\n\n- The Civil Aviation Safety Authority (under the Commonwealth Civil Aviation Regulations, Part 39) issues and enforces the directive; the directive requires operators to follow the Boeing service bulletin. (header; Requirement)\n- Aircraft operators and owners bear the cost of performing the inspections, any consequential repairs, and the operational scheduling needed to meet the landing-count intervals. (Requirement; Compliance)\n\nWhy the inspection is required\n\n- The directive states that cracks in the attach lugs, if undetected, could lead to loss of the horizontal stabilizer. The inspection aims to find such cracks before they grow to a critical size. (Background)\n\nPractical consequences, trade-offs and implementation points to watch\n\n- Cost and downtime: Operators will incur direct costs for inspections and repairs and may incur aircraft out-of-service time while inspections or repairs are carried out. (Requirement; Compliance)\n- Reliance on manufacturer's procedure: The required inspection is carried out according to a Boeing service bulletin; operators must have access to and follow that external technical document. That creates operational dependence on the manufacturer's inspection method. (Requirement)\n- Recordkeeping and scheduling: Compliance is measured by landing counts. Operators must track landings accurately and schedule inspections at or before the numeric thresholds specified. (Compliance)\n- Triggering events: A chord replacement or modification done under Option 1 of the Requirement Document resets the timing for the initial inspection (Compliance (b)). Operators who carry out such work must note the new landing-count starting point. (Compliance)\n- Enforcement: The directive is issued under the Commonwealth civil aviation framework and is enforceable by the relevant safety authority; operators must comply or face regulatory consequences. (header)\n\nNet behaviour change\n\n- Operators of the listed 737s must add or maintain a recurring inspection task tied to landing counts and to certain repair/modification events. The directive shifts the private choice of when to inspect to a rule-based schedule tied to aircraft usage and modification history. (Requirement; Compliance)\n\nOfficial rationale vs costs and incentives\n\n- The stated safety rationale is detection of attach-lug cracks to prevent loss of the horizontal stabilizer. (Background)\n- The directive imposes recurring inspection costs and operational scheduling constraints on a relatively narrow set of aircraft (by model and line number). Those who operate the listed aircraft concentrate the costs; the safety benefit is concentrated toward preventing a low-frequency, high-consequence failure. (Applicability; Background; Compliance)\n\nReferences to the instrument text\n\n- Applicability: lists affected models and line numbers. (Applicability)\n- Requirement: mandates inspection per Boeing S.B. 737-55-1033. (Requirement)\n- Compliance: sets landing-count thresholds for initial and repeat inspections and addresses chord replacement/modification. (Compliance)\n- Background: explains the safety risk the inspections aim to address. (Background)\n- Note: references FAA AD 86-12-05. (Note)"}},"importantCases":[],"_links":{"self":"/api/acts/ad-b737-11-horizontal-stabilizer-centre-section-rear-spar-upper-chord-attach-lugs","history":"/api/acts/ad-b737-11-horizontal-stabilizer-centre-section-rear-spar-upper-chord-attach-lugs/history","analysis":"/api/acts/ad-b737-11-horizontal-stabilizer-centre-section-rear-spar-upper-chord-attach-lugs/analysis","conflicts":"/api/acts/ad-b737-11-horizontal-stabilizer-centre-section-rear-spar-upper-chord-attach-lugs/conflicts","importantCases":"/api/acts/ad-b737-11-horizontal-stabilizer-centre-section-rear-spar-upper-chord-attach-lugs/important-cases","documents":"/api/acts/ad-b737-11-horizontal-stabilizer-centre-section-rear-spar-upper-chord-attach-lugs/documents"}}