{"id":"F2006B02101","name":"AD/AC/42 Amdt 7 - Wing Main Spar Lower Cap W.S. 24","slug":"ad-ac-42-amdt-7-wing-main-spar-lower-cap-w-s-24","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41331,"registerId":"commonwealth-F2006B02101-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/AC/42 Amdt 7 - Wing Main Spar Lower Cap W.S. 24","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)  \nTwin Commander (Gulfstream/Rockwell/ Aerocommander 500, 600 and 700) Series Aeroplanes\n\nAD/AC/42\n\nAmdt 7\n\n  \nWing Main Spar Lower Cap W.S. 24 8/93\n\nApplicability: Models 500, 500A, 500B, 500S, 500U, 520, 560, 560A, 560E, 560F, 680, 680E, 680F, 680F(P), 680FL, 680FL(P), 680T, 680V, 680W, 681, and 720.\n\nRequirement: 1. Serial numbers 1 to 1730 only\n\nThese aircraft were not fitted with a spar reinforcement when they left the factory. Unless already accomplished install a wing front spar external reinforcement kit in accordance with Aero Commander Service Change 81A or 81B.\n\n    2. All serial numbers\n\nAs required for the particular model and serial number, in accordance with Twin Commander SB 90C:\n\n    modify the aircraft to improve access to W.S. 24;\n\n    b. modify the spar radius to improve its fatigue quality;\n\n    c. modify adjacent structure to eliminate interference; and\n\n    d. inspect for cracks and corrosion in the spar cap.\n\nAs noted in Twin Commander SB 90C, aircraft that have complied with earlier revisions of SB 90 may require additional work.\n\nCompliance: 1. Install the reinforcement kit before the issue of an Australian Certificate of Airworthiness.\n\n    2. If at 22 July 1993 the aircraft has not already been modified and inspected at\n\nW.S. 24, do so within 500 hours after 22 July 1993.\n\nIf at 22 July 1993 the aircraft has already been modified and inspected at W.S. 24, do the next inspection within 500 hours of the last one. In both cases re-inspect no less frequently than every:\n\n    \\- 500 hours for normal usage; or\n\n    \\- 200 hours for survey usage; or\n\n    \\- 100 hours for low level (less than 1000 feet AGL) survey usage.\n\nBackground: Wing station 24 has had a long history of fatigue cracking, including several fatal wing separations. Some form of spar reinforcement is necessary to lower stresses, to slow crack growth, to allow a practical inspection interval.\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\nThis latest amendment introduces Revision C to Service Bulletin 90. Revision C adds some additional models to the inspection program, and reduces the inspection interval for survey aircraft based on recent \\- including Australian - experience which indicates rapid crack growth under the severe flight loads experienced during such operations.\n\nAnother change is the elimination of the threshold for modification and inspection. Cracks have been found that probably started earlier. All aircraft must now be inspected regardless of hours flown.","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":4,"scope_assessment":{"changed":true,"description":"Yes. The amendment (Revision C to SB 90) broadens scope by adding additional models to the inspection program, reducing inspection intervals for survey operations, and eliminating the prior hours‑based threshold so that all affected aircraft must be inspected regardless of hours flown (Amendment summary). This change increases the population subject to inspection and tightens intervals for higher‑risk operations."},"complexity_factors":["Serial-number conditional requirement: install reinforcement kit only for serials 1–1730 (Requirement: 1).","Multiple technical documents referenced: installation per Aero Commander Service Change 81A/81B and modifications/inspections per Twin Commander SB 90C (Requirement: 1; Requirement: 2).","Several discrete modification tasks required (improve access, modify spar radius, modify adjacent structure, inspect for cracks/corrosion) creating multi-step work and potential coordination with maintenance facilities (Requirement: 2 a–d).","Staggered compliance timing and re‑inspection logic (install before Australian Certificate of Airworthiness for some; otherwise within 500 hours of 22 July 1993 or within 500 hours of last inspection) creates record‑keeping and scheduling burdens (Compliance: 1; Compliance: 2).","Different inspection intervals tied to operational use (500 hours normal; 200 hours survey; 100 hours low‑level survey) requires operators to classify usage and track flight hours precisely (Compliance: 2).","Removal of a previous threshold for modification/inspection expands applicability and may require inspections regardless of aircraft hours flown (Amendment summary).","Potential need for additional work where earlier SB revisions were complied with, increasing uncertainty about exact scope of required work on some aircraft (Requirement: 2 note)."],"plain_english_summary":"This Airworthiness Directive requires installation of a wing front spar external reinforcement kit on earlier Twin Commander models and mandates modifications and repeated inspections of the wing main spar lower cap (W.S. 24) on all listed models to detect and slow fatigue cracking. Aircraft owners/operators must arrange and pay for the modifications and inspections; the Civil Aviation Safety Authority sets the deadlines and inspection intervals, which are shortened for survey and low‑level survey operations."},"kimi_summary":{"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":true,"description":"The original directive likely applied only to higher-hour aircraft or had a threshold before inspections were required. Amendment 7 significantly expanded the scope by: (1) eliminating the hours-flown threshold so ALL aircraft must be inspected regardless of age or usage; (2) adding additional aircraft models to the inspection program via SB 90C Revision C; and (3) introducing more frequent inspection intervals for survey operations based on Australian operational data showing faster crack propagation than originally anticipated."},"complexity_factors":["Short, single-purpose directive focused on one mechanical issue","Only 4 defined model categories (serial number ranges and usage types)","Simple conditional structure: two main compliance paths based on serial number and modification status","Clear, specific deadlines (500 hours from date, or since last inspection)","Minimal cross-referencing (only references to specific Service Bulletins: 81A, 81B, and 90C)","No nested exceptions or complex definitional sections"],"plain_english_summary":"This CASA Airworthiness Directive for specific Twin Commander models requires urgent structural modifications, inspections and a reinforcement kit to stop fatigue cracking at Wing Station 24 that has led to fatal wing separations. It affects owners/operators by forcing access-mods, crack/corrosion inspections on all affected aircraft and mandatory kit installation for older serials before Australian certification. Amendment 7 removes prior exemptions and tightens recurring inspection intervals, reflecting faster crack growth in low‑level/survey operations — a life‑critical safety requirement."},"flash_summary_failed":{"failed":true,"reason":"A positive credit balance is required for all requests, including BYOK, so fallback providers remain available. Add credits at https://vercel.com/d?to=%2F%5Bteam%5D%2F%7E%2Fai%3Fmodal%3Dtop-up to continue.","source":"analysis-cron"}},"importantCases":[],"_links":{"self":"/api/acts/ad-ac-42-amdt-7-wing-main-spar-lower-cap-w-s-24","history":"/api/acts/ad-ac-42-amdt-7-wing-main-spar-lower-cap-w-s-24/history","analysis":"/api/acts/ad-ac-42-amdt-7-wing-main-spar-lower-cap-w-s-24/analysis","conflicts":"/api/acts/ad-ac-42-amdt-7-wing-main-spar-lower-cap-w-s-24/conflicts","importantCases":"/api/acts/ad-ac-42-amdt-7-wing-main-spar-lower-cap-w-s-24/important-cases","documents":"/api/acts/ad-ac-42-amdt-7-wing-main-spar-lower-cap-w-s-24/documents"}}