{"id":"F2006B05493","name":"AD/PA-23/66 Amdt 2 - Wing Structural Fatigue Limitation","slug":"ad-pa-23-66-amdt-2-wing-structural-fatigue-limitation","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":46328,"registerId":"commonwealth-F2006B05493-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/PA-23/66 Amdt 2 - Wing Structural Fatigue Limitation","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)  \nPiper PA-23 (Apache and Aztec) Series Aeroplanes\n\nAD/PA-23/66\n\nAmdt 2\n\n  \nWing Structural Fatigue Limitation 12/89\n\nApplicability: All models certificated at a MTOW of 4800 lb or greater. Requirement: Retire the main spar lower cap assembly from service.\n\nCompliance: 1. For aircraft certificated at a MTOW of 5200 lbs, prior to exceeding 13000 hours component time in service.\n\n    2. For aircraft certificated at a MTOW of 4940 lbs, prior to exceeding 20700 hours component time in service.\n\n    3. For aircraft certificated at a MTOW of 4800 lbs, prior to exceeding 27300 hours component time in service.\n\n    4. For aircraft certificated at a MTOW of 5200 lbs and fitted with Met-Co-Aire wing tip fuel tanks, prior to exceeding N hours component time in service where N is given by the expression:\n\nN \\= 13000 + (13000 \\- T) x 0.593 hours,\n\nwhere T \\= lower main spar cap time in service at which tip tanks were fitted.\n\nNote: The available fatigue data covers wing main spars only. The durability of other parts of the airframe has not been evaluated, and is therefore unknown.\n\nBased on experience, the Authority is prepared to credit unevaluated structure with a retirement life equal to double the life for the lower main spar cap.\n\nAn extension may be available, but any application must be supported by a fatigue substantiation covering all the remaining primary structure. This should include empennage, wing centre section, wing rear spar, control surfaces, fuselages, etc.\n\nThe substantiation may take the form of a safe life assessment, or a sufficiently rigorous revised inspection schedule to ensure that any fatigue cracking which could occur in service will be detected before the aircraft is endangered.\n\nBackground: The retirement lives promulgated by this Directive have been determined on the basis of information provided by the manufacturer. Operation beyond the promulgated lives carries an unacceptable risk of the spar cap developing fatigue cracks.\n\nThis Amendment introduces retirement lives for 4800 and 4940 lb MTOW aircraft, as well as aircraft fitted with Met-Co-Aire wing tip fuel tanks.","sortOrder":0}],"analysis":{"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"},"kimi_summary":{"content_quality":"ok","complexity_score":4,"scope_assessment":{"changed":true,"description":"This Amendment 2 significantly expanded the original directive's scope. The original AD/PA-23/66 (implied by the Background section) apparently only covered 5,200 lb aircraft. This amendment adds coverage for 4,800 lb and 4,940 lb MTOW categories, plus a complex formula for aircraft with Met-Co-Aire wing tip fuel tanks. The directive has evolved from a simple hour limit for one weight class to a multi-tiered, calculation-dependent system covering multiple configurations."},"complexity_factors":["Multiple applicability tiers based on weight categories (4800, 4940, 5200 lb MTOW)","Mathematical formula required for aircraft with Met-Co-Aire wing tip fuel tanks (N = 13000 + (13000 - T) x 0.593)","Cross-references to undefined variables requiring operator calculation (T = time when tip tanks fitted)","Conditional compliance structure with four distinct pathways","Implicit extension provisions requiring 'fatigue substantiation' without defined procedural standards","Technical aviation terminology requiring specialized knowledge (MTOW, empennage, safe life assessment, substantiation)"],"plain_english_summary":"This Airworthiness Directive requires mandatory retirement and replacement of the main spar lower cap assembly on Piper PA‑23 Apache/Aztec aircraft certified at 4,800 lb MTOW or heavier, with specific flight‑hour limits by weight (e.g. ~13,000–27,300 hours) and a special formula for aircraft fitted with extra tanks. It’s aimed at preventing metal‑fatigue failure of a critical wing backbone; flying beyond those lives risks catastrophic structural failure. Other structures aren’t covered without further engineering approval."},"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":true,"description":"This amendment expands the retirement‑life regime by adding explicit retirement lives for aircraft certificated at 4800 lb and 4940 lb MTOW and for aircraft fitted with Met‑Co‑Aire wing tip fuel tanks, thereby broadening which PA‑23 variants must meet fixed component‑hour limits (see final paragraph)."},"complexity_factors":["Multiple MTOW‑based retirement thresholds with different hour limits (Compliance 1–3) increase operator tracking complexity.","Conditional retirement life computed by a formula when Met‑Co‑Aire tip tanks are fitted, requiring knowledge of T (lower spar cap time when tanks fitted) and calculation (Compliance 4).","Mandatory retirement of a specific structural component (main spar lower cap assembly) creates a clear compliance action but imposes replacement cost on owners/operators (Requirement & Compliance).","Extension process requires a comprehensive fatigue substantiation covering all remaining primary structure (empennage, wing centre section, wing rear spar, control surfaces, fuselages, etc.), imposing a high technical and evidentiary burden on applicants (post‑Note paragraph).","Regulator discretion to credit unevaluated structure with double the spar cap life introduces interpretive variability that operators must understand and document (Note).","Recordkeeping and proof requirements: operators must maintain accurate component time‑in‑service to apply the formula and to support any extension application (Compliance 4 & extension paragraph).","Safety‑based termination point: the Background states operation beyond promulgated lives carries 'an unacceptable risk' of spar cap cracking, which tightens enforcement expectations but does not itself specify inspection details (Background & Note)."],"plain_english_summary":"This airworthiness directive requires retiring (removing from service) the main spar lower cap assembly on Piper PA‑23 (Apache/Aztec) aeroplanes certificated at MTOW ≥ 4800 lb, at specific component‑hour limits that vary by MTOW and if Met‑Co‑Aire wing tip tanks are fitted (a formula applies). \n\nAircraft owners/operators must monitor spar cap time‑in‑service and replace the part; extensions are possible only with a full fatigue substantiation covering all primary structure."}},"importantCases":[],"_links":{"self":"/api/acts/ad-pa-23-66-amdt-2-wing-structural-fatigue-limitation","history":"/api/acts/ad-pa-23-66-amdt-2-wing-structural-fatigue-limitation/history","analysis":"/api/acts/ad-pa-23-66-amdt-2-wing-structural-fatigue-limitation/analysis","conflicts":"/api/acts/ad-pa-23-66-amdt-2-wing-structural-fatigue-limitation/conflicts","importantCases":"/api/acts/ad-pa-23-66-amdt-2-wing-structural-fatigue-limitation/important-cases","documents":"/api/acts/ad-pa-23-66-amdt-2-wing-structural-fatigue-limitation/documents"}}