{"id":"F2006B05755","name":"AD/PA-31/51 Amdt 1 - Flap Transmission - Inspection","slug":"ad-pa-31-51-amdt-1-flap-transmission-inspection","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"repealed","isInForce":false,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":135606,"registerId":"commonwealth-F2006B05755-current","compilationNumber":null,"startDate":"2026-04-03","status":"Repealed","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/PA-31/51 Amdt 1 - Flap Transmission - Inspection","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-31 Series Aeroplanes\n\nAD/PA-31/51\n\nAmdt 1\n\n  \nFlap Transmission \\- Inspection 10/83\n\nApplicability: Models PA-31, PA-31-300 and PA-31-325 with S/Nos. 31-2 to 31-7812129. Model PA-31-350 with S/Nos. 31-5001 to 31-7852171. Model PA-31P with S/Nos. 31P-1 to 31P-7730012. Model PA-31T with S/Nos. 31T-7400002 to 31T-7820092. Model\n\nPA31T1 with S/Nos. 31T-7804001 to 31T-7804011. Except aircraft which have incorporated Piper SL 959.\n\nDocuments: 1. Piper SB No. 494B, Instruction No. 1; or\n\n2. Piper SL No. 764A, Instruction No. 1.\n\nCompliance: Within 25 hours time in service after 28 October 1976 and thereafter at intervals not exceeding 100 hours time in service.\n\nNote: Compliance with Section 2 of AD/PA-31/44 within the past 100 hours time in service satisfies compliance with the 25 hour requirement of this Directive.\n\nBackground: Piper SL 959 introduces an optional flap control system which restores 40o flap movement and relieves the specific inspections on some aircraft.","sortOrder":0}],"analysis":{"kimi_summary":{"_metrics":{"model":"kimi-k2.5","source":"moonshot-batch","completionTokens":2271},"content_quality":"ok","complexity_score":3,"scope_assessment":{"changed":false,"description":"This amendment (Amdt 1) maintains the original scope of ensuring airworthiness of Piper PA-31 flap transmission systems. While the text has been updated from the original 1976 directive (likely to refine applicability or compliance dates), it remains tightly focused on the specific safety inspection requirements for the identified aircraft models and has not expanded to unrelated systems or aircraft types."},"complexity_factors":["Six different aircraft model/serial number combinations in the applicability section","External cross-references to three separate Piper technical documents (SB 494B, SL 764A, SL 959)","Reference to another Airworthiness Directive (AD/PA-31/44) for compliance equivalency","Technical aviation terminology requiring domain knowledge (e.g., 'Time in Service', 'flap transmission')"],"plain_english_summary":"**What this does:** This is a mandatory safety instruction (called an Airworthiness Directive) requiring owners of specific Piper PA-31 aircraft to regularly inspect the **flap transmission** — the mechanical system that controls the flaps (the moving parts on wings that help slow the plane down for landing).\n\n**Who it affects:** Owners and operators of Piper PA-31, PA-31-300, PA-31-325, PA-31-350, PA-31P, PA-31T, and PA31T1 aircraft with specific serial numbers listed in the document. It does **not** apply to aircraft that have already been modified according to Piper Service Letter 959.\n\n**What must be done:**\n*   Inspect the flap transmission system within 25 hours of flying time after 28 October 1976\n*   Repeat the inspection every 100 hours of flying time thereafter\n*   Follow the specific instructions in Piper Service Bulletin 494B or Service Letter 764A\n\n**The shortcut:** If you've already complied with another directive (AD/PA-31/44) within the last 100 hours, that counts as satisfying the initial 25-hour inspection requirement.\n\n**Why it matters:** The directive prevents mechanical failures in the flap control system that could affect safe landing. The optional modification mentioned (Piper SL 959) restores full 40-degree flap movement and removes the need for these specific inspections."},"summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This instrument is the current version of Airworthiness Directive AD/PA-31/51 (Amendment 1), setting out continuing airworthiness requirements."},"complexity_factors":["Relies on specific external service documents (Piper SB 494B or SL 764A)","Exemptions depend on incorporation of an optional modification (Piper SL 959)","References another airworthiness directive (AD/PA-31/44) for a credit provision","Specifies both a one-off initial compliance date and repetitive intervals"],"plain_english_summary":"This AD requires repetitive inspections of the flap transmission system on specified Piper PA-31 series aircraft (within the stated serial number ranges) to detect and prevent defects that could cause asymmetric or uncontrolled flap operation. It applies to Australian-registered aircraft unless Piper Service Letter 959 (an optional flap-control modification) has been embodied.\n\nThe initial inspection is due within 25 hours TIS after 28 Oct 1976, then at intervals not exceeding 100 hours, using Piper Service Bulletin No. 494B or Service Letter No. 764A, and must be recorded in the maintenance log."}},"importantCases":[],"_links":{"self":"/api/acts/ad-pa-31-51-amdt-1-flap-transmission-inspection","history":"/api/acts/ad-pa-31-51-amdt-1-flap-transmission-inspection/history","analysis":"/api/acts/ad-pa-31-51-amdt-1-flap-transmission-inspection/analysis","conflicts":"/api/acts/ad-pa-31-51-amdt-1-flap-transmission-inspection/conflicts","importantCases":"/api/acts/ad-pa-31-51-amdt-1-flap-transmission-inspection/important-cases","documents":"/api/acts/ad-pa-31-51-amdt-1-flap-transmission-inspection/documents"}}