{"id":"F2006B06368","name":"AD/PT6A/32 - Exhaust Duct Cracking","slug":"ad-pt6a-32-exhaust-duct-cracking","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":47621,"registerId":"commonwealth-F2006B06368-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"AIRWORTHINESS DIRECTIVE","sectionType":"part","heading":"AIRWORTHINESS DIRECTIVE","content":"# ![](image.001.png)  \nAIRWORTHINESS DIRECTIVE\n\nFor the reasons set out in the background section, the CASA delegate whose signature appears below issues the following Airworthiness Directive (AD) under subregulation 39.1 (1) of CAR 1998. The AD requires that the action set out in the requirement section (being action that the delegate considers necessary to correct the unsafe condition) be taken in relation to the aircraft or aeronautical product mentioned in the applicability section: (a) in the circumstances mentioned in the requirement section; and (b) in accordance with the instructions set out in the requirement section; and (c) at the time mentioned in the compliance section.\n\n![](image.001.png)\n\nPratt and Whitney Canada Turbine Engines \\- PT6A Series","sortOrder":0},{"sectionNumber":"AD/PT6A/32 Exhaust Duct Cracking 3/2003","sectionType":"part","heading":"AD/PT6A/32 Exhaust Duct Cracking 3/2003","content":"# AD/PT6A/32 Exhaust Duct Cracking 3/2003\n\nApplicability: All PT6A-6, \\-6A, \\-6B, \\-11, \\-11AG, \\-15AG, \\-20, \\-20A, \\-20B, \\-21, \\-25, \\-25A, \\-25C, \\-\n\n27, \\-28, \\-34, \\-34AG, \\-34B, \\-36, \\-110, \\-112, \\-135, and –135A series turboprop engines fitted with turbine exhaust ducts that are not in compliance with Pratt and Whitney Canada (P&WC) Service Bulletins (SB) 1610, 1610R1, 1610R2 or 12173R1.\n\nRequirement: 1. Inspect the turbine exhaust duct for low-quality welds, created during repair, on the turbine exhaust duct near flange “A”, in accordance with Paragraphs 3B through 3E of:\n\n    P&WC SB PT6A-72-1610 Revision 2 for models PT6A-6, -6A, -6B, -20, - 20A, \\-20B, \\-21, \\-25, \\-25A, \\-25C, \\-27, \\-28, \\-34, \\-34AG, \\-34B, \\-36, \\-135, and \\- 135A engines; or\n\n    b. P&WC SB PT6A-72-12173 Revision 1 for models PT6A-11, \\-11AG, \\- 15AG, -110, and -112 engines.\n\n    2. If it is determined that the welds meet acceptable criteria as detailed in Requirement 1a or 1b of this Directive:\n\n    Return the duct to service.\n\n    b. Carry out an internal inspection of the exhaust duct for cracking in accordance with the applicable P&WC Engine Overhaul Manual.\n\n    3. If it is determined that the welds do not meet acceptable criteria as detailed in Requirement 1a or 1b of this Directive:\n\n    Replace the duct with a serviceable part; or\n\n    b. Carry out an inspection as detailed in Requirement 4 of this Directive.\n\n    4. Use a 5x magnification to visually inspect the circumference of the forward area of the exhaust duct from the propeller reduction gearbox mounting flange to 2 inches aft of the flange for any crack indication:\n\n    If no cracks are found, return the duct to service and repeat the initial inspection as detailed in Requirement 4 at the detailed interval.","sortOrder":1},{"sectionNumber":"Pratt and Whitney Canada Turbine Engines","sectionType":"part","heading":"Pratt and Whitney Canada Turbine Engines - PT6A Series","content":"## Pratt and Whitney Canada Turbine Engines \\- PT6A Series\n\nAD/PT6A/32 (Continued)\n\n    b. If cracks are found exceeding the limits below, replace the duct with a serviceable part;\n\n    If 3 or less cracks are found, and the total cumulative length of the cracks exceeds 2 inches; or\n\n    ii. If any one crack exceeds 1 inch in length; or\n\n    iii. If any 2 cracks are separated by less than 6 times the longest crack (6L) or 3 inches or less, whichever is the closest separation; or\n\n    iv. If more than 3 cracks are found.\n\n    c. If cracks are found that are within the limits set by requirement 4b(i) through\n\n(iv) of this Directive, mark all allowable cracks on the duct with a suitable metal marking material; and record the length of the crack, location, number of duct operating hours, and time since overhaul; and\n\n    Repeat the inspection and replace ducts exceeding the limits of Requirement 4b(i) through (iv) of this Directive;\n\n    ii. Monitor the growth of existing cracks. For cracks exceeding a growth rate of 0.015 inches per hour time in service since the last inspection, replace the duct with a serviceable part.\n\nNote 1: Canadian AD CF 2002-47 refers.\n\nNote 2: Suitable marking materials can be found in the PWC Engine Manual.\n\nNote 3: A replacement duct is one that meets the acceptability limits of this Directive.\n\nCompliance: 1. At the next shop visit or within 150 flight hours from the effective date of this Directive, whichever occurs first.\n\n    2. a. At the completion of Requirement 1 of this Directive.\n\nb. At the next overhaul.\n\n    3. Prior to further flight.\n\n    4. a. At intervals not to exceed 150 flight hours.\n\n    b. Prior to further flight.\n\n    c. At intervals not to exceed 25 flight hours.\n\nThis Airworthiness Directive becomes effective on 20 March 2003.","sortOrder":2}],"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":false,"description":"This AD maintains its original narrow scope — addressing a specific welding defect in PT6A exhaust ducts. The detailed crack measurement criteria and tiered inspection requirements reflect the technical precision needed for aviation safety rather than scope creep."},"complexity_factors":["Multiple nested conditional pathways (Requirements 1-4 with sub-clauses a, b, c, and roman numeral sub-sub-clauses)","Cross-references to four external Pratt & Whitney Canada Service Bulletins and Engine Overhaul Manuals","Precise technical measurement thresholds (2 inches cumulative, 1 inch single crack, 6L separation rule, 0.015 inch growth rate)","Multiple compliance timelines that vary by requirement and inspection outcome (150 flight hours, 25 flight hours, 'next shop visit', 'prior to further flight')","18 different engine model variants listed in applicability section with two different service bulletin pathways","Technical terminology requiring aviation engineering knowledge (flange 'A', propeller reduction gearbox, time since overhaul)"],"plain_english_summary":"This CASA safety order requires operators and maintainers of Pratt & Whitney Canada PT6A engines (‑6 through ‑135A series), unless already modified per specific factory service bulletins, to inspect and address welded turbine exhaust ducts that can develop dangerous cracks.  \n\nIts aim is to catch and fix weld-related cracking within a defined short timeframe to prevent catastrophic outcomes — such as propeller gearbox separation or loose turbine blades — by mandating timely inspection and corrective action."},"flash_summary":{"complexity_score":5,"scope_assessment":{"changed":false,"description":"The AD stays within its original, stated safety purpose: to detect and correct exhaust duct cracking that developed after repairs using a different welding process. The directive's measures — inspections, marking, monitoring and replacement thresholds — are narrowly targeted to that hazard and to PT6A models whose ducts are not already modified per the cited P&WC Service Bulletins. There is no indication in the text that the directive's scope has been expanded beyond addressing that specific unsafe condition (Background; Applicability; Requirements 1–4)."},"complexity_factors":["Applicability lists a large number of distinct PT6A engine models (multi-model scope).","Cross-references to multiple external documents: P&WC SB PT6A-72-1610 Rev 2, PT6A-72-12173 Rev 1, and the P&WC Engine Overhaul Manual (Requirement 1; Requirement 2).","Layered conditional logic: actions depend first on weld acceptability (Requirement 1–3), then on crack presence and measured thresholds (Requirement 4 and subparts).","Multiple numeric thresholds and limits for cracks: single-crack length (1 inch), cumulative length (2 inches for up to 3 cracks), crack separation rules (6L or 3 inches), count limits (>3 cracks) (Requirement 4b(i)–(iv)).","Mixed inspection methods and intervals: initial inspection at next shop visit or 150 flight hours, recurring inspections at 150 flight hours, overhaul-scheduled internal inspections, and short 25-hour monitoring intervals for marked cracks (Compliance).","A growth-rate trigger expressed as a numeric rate (0.015 inches per hour time in service since last inspection) requiring measurement and time-tracking (Requirement 4c(ii)).","External noting and dependence on related foreign AD (Canadian AD CF 2002-47) and unspecified acceptable marking materials in the P&WC manual (Notes 1–3).","No definitions section in the AD itself for some operational terms (e.g., 'serviceable part'), relying on notes and external manuals for interpretation (Note 3)."],"plain_english_summary":"**What this instrument does (mechanically)**\n\n- This Airworthiness Directive (AD) requires inspections and, where necessary, replacement or monitoring of turbine exhaust ducts on a range of Pratt & Whitney Canada PT6A turboprop engines that do not already comply with specified P&WC Service Bulletins (SBs) (Applicability; Requirement 1).\n- It mandates:\n  - A visual inspection for low-quality welds near flange “A” following the procedures in the referenced P&WC SBs (Requirement 1);\n  - If welds are acceptable, an internal inspection per the P&WC Engine Overhaul Manual and return-to-service actions (Requirement 2);\n  - If welds are unacceptable, immediate replacement of the duct before further flight or a more detailed crack inspection (Requirement 3);\n  - A 5× visual inspection of the forward circumference of the exhaust duct (from the propeller reduction gearbox mounting flange to 2 inches aft) for cracks, with clear numeric limits that trigger mandatory replacement, or else marking and monitoring of allowable cracks (Requirement 4 and subparts).\n- The AD sets specific thresholds for action (for example: replace the duct if any single crack exceeds 1 inch, if total crack length of up to 3 cracks exceeds 2 inches, if more than 3 cracks are found, or if separations between cracks are below defined limits) and requires marking, recording and growth-rate monitoring for cracks that are initially acceptable. If crack growth exceeds 0.015 inches per hour of time-in-service since the last inspection, the duct must be replaced (Requirement 4b–c).\n- It cross-references P&WC Service Bulletins PT6A-72-1610 Rev 2 or PT6A-72-12173 Rev 1, the P&WC Engine Overhaul Manual, and notes the related Canadian AD CF 2002-47 (Requirement 1; Note 1).\n\n**Who this affects**\n\n- Aircraft owners and operators using the listed PT6A engine models whose exhaust ducts are not already modified to comply with the named P&WC SBs (Applicability).\n- Approved maintenance organisations, overhaul shops and technicians who must perform the inspections, mark and record crack data, and replace ducts when required (Requirements 1–4; Compliance).\n- Parts suppliers, because ducts must be serviceable (Note 3) and unacceptable repaired ducts will be taken out of service (Requirement 3; Note 3).\n\n**Why it matters (safety and mechanical rationale)**\n\n- The AD responds to cracking that developed after repairs using a different welding process. The stated safety risk is that excessive exhaust duct cracking could lead to reduction gearbox separation or decoupling of the power turbine shaft and, ultimately, release of turbine blades (Background).\n\n**How it works in practice (timing and frequency)**\n\n- Initial inspection: at the next shop visit or within 150 flight hours from the AD effective date, whichever comes first (Compliance 1).\n- Follow-up and recurring inspections: internal inspection at next overhaul (Compliance 2b); scheduled repetition of the 5× visual inspection at intervals not to exceed 150 flight hours (Requirement 4a / Compliance 4a); if cracks are marked and monitored, repeat inspections at intervals not to exceed 25 flight hours (Compliance 4c(iii)). If welds are judged unacceptable, replacement is required before further flight (Requirement 3; Compliance 3).\n\n**Practical effects, incentives and costs**\n\n- Who pays: aircraft operators bear the direct costs — shop labour, inspection time, possible duct replacement parts, and aircraft downtime for inspections or part changes (Requirements 1–4; Compliance).\n- Behaviour changes required: operators must stop returning ducts repaired with the earlier welding method to service without inspection; maintenance shops must adopt the SB inspection procedures and document/mark cracks and their measurements (Requirement 1; Requirement 4c).\n- Compliance burden: multiple, recurring inspections with different intervals (150 flight hours, overhaul cadence, and 25-hour monitoring intervals) plus record-keeping of crack lengths, locations, operating hours and time since overhaul (Requirement 4c).\n- Supply and timing risk: if many operators need replacement ducts quickly, parts availability and lead times could cause additional downtime or higher costs (implicit from Requirement 3 and Note 3).\n- Effects on repair choices and aftermarket: the AD restricts the practical acceptability of ducts repaired with the different welding process unless they meet the SB criteria. That reduces the option to reuse lower-cost repaired ducts that fail the inspection criteria (Requirement 1; Requirement 3).\n\n**Trade-offs, implementation risks and measurement issues**\n\n- Measurement and detection risk: the AD relies primarily on a 5× visual inspection and simple length/separation thresholds. That method risks missing subsurface or very fine cracks that non‑destructive testing might detect; the AD does require internal inspections per the Overhaul Manual in some circumstances (Requirement 2; Requirement 4).\n- Monitoring accuracy and enforcement: the growth-rate threshold (0.015 inches per hour time in service since the last inspection) requires consistent measurement and record-keeping to enforce (Requirement 4c(ii)).\n- Administrative discretion: the AD references external manufacturer's SBs and the Engine Overhaul Manual for procedures and acceptable repair limits, so implementation depends on interpretation and application of those external documents by maintenance organisations (Requirement 1; Requirement 2).\n\n**References inside the AD (where to look for the procedures and limits)**\n\n- Applicability — lists the exact PT6A models covered.\n- Requirement 1 — refers to specific P&WC Service Bulletins for weld inspection procedures.\n- Requirement 2–4 — set out actions after inspection, crack measurement thresholds, marking, monitoring and replacement rules.\n- Compliance — sets initial and recurring inspection timing (next shop visit, within 150 flight hours, next overhaul, prior to further flight, 150‑hour and 25‑hour intervals).\n- Background and Notes — explain reason (different welding process led to cracks) and cross-reference Canadian AD CF 2002-47.\n\nThe instrument is a targeted, prescriptive safety directive: it tells operators and maintenance organisations precisely what inspections to perform, what limits trigger replacement, how often to inspect, and what records to keep. It increases maintenance workload and parts demand for affected PT6A engines and restricts the continued use of ducts repaired by the different welding method unless they meet the specified acceptance criteria (Applicability; Requirements 1–4; Compliance)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-pt6a-32-exhaust-duct-cracking","history":"/api/acts/ad-pt6a-32-exhaust-duct-cracking/history","analysis":"/api/acts/ad-pt6a-32-exhaust-duct-cracking/analysis","conflicts":"/api/acts/ad-pt6a-32-exhaust-duct-cracking/conflicts","importantCases":"/api/acts/ad-pt6a-32-exhaust-duct-cracking/important-cases","documents":"/api/acts/ad-pt6a-32-exhaust-duct-cracking/documents"}}