{"id":"F2006B02440","name":"AD/APU/8 - Garrett APU Compressor Rotating Group","slug":"ad-apu-8-garrett-apu-compressor-rotating-group","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":41696,"registerId":"commonwealth-F2006B02440-current","compilationNumber":null,"startDate":"2026-04-01","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/APU/8 - Garrett APU Compressor Rotating Group","content":"COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 \\- 107 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n![](image.001.png)  \nAuxiliary Power Units\n\nAD/APU/8 Garrett APU Compressor Rotating Group 4/93\n\nApplicability: Garrett Model GTCP 36-300,-280\\[B\\] and -280\\[D\\] Requirement: Action in accordance with Garrett Service Bulletins:\n\nA. For the GTCP36-300, GTCP36-49-A6642 1 May 1992.\n\nB. For the GTCP36-280, GTCP36-49-A6653 1 May 1992.\n\nNote: FAA AD 92-21-05 refers.\n\nCompliance: To be completed by 30 September 1995.\n\nBackground: There have been two incidents in which rim separation in the dampening groove of the load compressor has resulted in rotating group unbalance severe enough to cause tieshaft failure just aft of the compressor shaft. The resultant translational energy caused the compressor shafts to exit the APU inlet plenum and penetrate the aircraft firewall. This directive involves rework of the load and engine compressors and replacement of the compressor shaft.","sortOrder":0}],"analysis":{"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-bound safety directive addressing a specific mechanical failure mode in specific engine models. It has not expanded beyond its original purpose of mandating repairs to prevent compressor shaft failures."},"complexity_factors":["Very short document (approximately 150 words)","Only 3 defined model variants (GTCP 36-300, -280[B], -280[D])","Single compliance requirement with reference to external technical documents (Service Bulletins)","No nested exceptions or conditional logic","Simple linear structure: applicability → requirement → compliance date → background","Cross-reference to one FAA AD (92-21-05) and two manufacturer service bulletins only"],"plain_english_summary":"This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA). It requires specific repairs to certain aircraft engines.\n\n**What it does:**\nOrders owners and operators of specific **Garrett auxiliary power units (APUs)** — small turbine engines that provide power to aircraft when the main engines are off — to perform urgent maintenance on the compressor rotating group.\n\n**Who it affects:**\nAnyone operating aircraft with **Garrett Model GTCP 36-300, -280[B], or -280[D] APUs**. These are commonly found in regional and business aircraft.\n\n**What must be done:**\n- **For GTCP36-300 models:** Follow Garrett Service Bulletin GTCP36-49-A6642 (dated 1 May 1992)\n- **For GTCP36-280 models:** Follow Garrett Service Bulletin GTCP36-49-A6653 (dated 1 May 1992)\n\nThe work involves reworking the load and engine compressors and replacing the compressor shaft.\n\n**Why it matters:**\nTwo serious incidents occurred where the compressor rim separated in the \"dampening groove\" (a groove designed to reduce vibration). This caused such severe imbalance that the connecting shaft broke. The resulting force was so violent that compressor shafts shot out of the engine, broke through the aircraft's firewall, and could have caused catastrophic damage or loss of life.\n\n**Deadline:**\nAll work had to be completed by **30 September 1995**.\n\n**Key point:** This is not optional. Airworthiness Directives are legally binding safety mandates. Non-compliance means the aircraft cannot legally fly."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"Based solely on the text provided, the directive sets out corrective actions for the Garrett GTCP36-300 and GTCP36-280(-280[B], -280[D]) APUs and requires compliance with specified Garrett Service Bulletins by a fixed date. There is no language in the instrument indicating an expansion or contraction of the set of affected equipment or the required actions compared with the directive as presented (Applicability, Requirement, Compliance, Background)."},"complexity_factors":["Technical specificity: actions concern compressor rotating group rework and shaft replacement (Requirement, Background).","References to external documents: compliance depends on following two Garrett Service Bulletins dated 1 May 1992 (Requirement).","Safety-critical consequences: failure mode described involves shaft ejection and firewall penetration, increasing urgency and need for correct execution (Background).","Fixed compliance deadline: a single completion date (30 September 1995) creates scheduling pressure (Compliance).","Limited scope but precise applicability: only certain Garrett GTCP36 models are affected (Applicability).","No explicit alternative methods of compliance or exemption stated in the text, which reduces implementer flexibility (Requirement, Compliance)."],"plain_english_summary":"### What this directive does, in plain English\n\nThis airworthiness directive requires specific maintenance work on certain Garrett auxiliary power units (APUs). It applies to Garrett GTCP36-300 and GTCP36-280 series (models -280[B] and -280[D]) APUs (Applicability). The directive requires operators to carry out the actions set out in two Garrett Service Bulletins dated 1 May 1992: GTCP36-49-A6642 for the GTCP36-300 and GTCP36-49-A6653 for the GTCP36-280 (Requirement). The required work involves reworking the load and engine compressors and replacing the compressor shaft (Background). All required actions must be completed by 30 September 1995 (Compliance). The directive also notes a corresponding FAA airworthiness directive (Note).\n\n### Why the regulator issued this\n\nThe directive cites two incidents where a rim separation in a compressor dampening groove produced enough rotating unbalance to break a tieshaft just aft of the compressor shaft. The resulting energy caused compressor shafts to exit the APU inlet plenum and penetrate the aircraft firewall (Background). The stated purpose is to remove the risk by reworking the compressors and replacing the compressor shaft in affected units (Requirement, Background).\n\n### Who is affected and who pays\n\n- Affected: aircraft owners/operators whose aircraft use the Garrett GTCP36-300 or GTCP36-280 (models -280[B] and -280[D]) APUs (Applicability). \n- Who pays: operators/owners will bear the costs of implementing the Service Bulletin work (rework and shaft replacement), any required parts, labour and aircraft downtime (Requirement, Background, Compliance).\n\n### What changes in behaviour and operation\n\n- Operators must schedule and complete the specific Service Bulletin work on each affected APU by the compliance date (Compliance, Requirement). \n- Maintenance organizations must perform rework and replace compressor shafts in accordance with the manufacturer's Service Bulletins (Requirement).\n\n### Practical trade-offs, incentives and implementation points to note\n\n- Cost versus risk: the directive forces an upfront maintenance cost and aircraft downtime in order to eliminate a mechanical failure mode that has led to shaft ejection and firewall penetration in two incidents (Background, Requirement). Operators weigh those direct costs and downtime against the safety risk the regulator describes. \n- Reliance on manufacturer instructions: the directive mandates compliance with particular Garrett Service Bulletins rather than setting a technical specification itself, so implementers follow the manufacturer’s procedures (Requirement). \n- External coordination: the directive references an FAA AD, indicating regulatory alignment or parallel action by a foreign regulator (Note). \n- Discretion and alternatives: the text does not state any alternate methods of compliance or exemptions; it sets a fixed compliance date and specific service bulletin references (Requirement, Compliance). \n- Implementation risk: work involves dismantling and reworking rotating compressor components and replacing shafts, which requires appropriate maintenance capability, parts availability and aircraft downtime (Background, Requirement). \n\n### Net effect on markets and operators (mechanically stated)\n\n- Private maintenance providers and operators must perform specified repair and replacement work on the listed APU models, which creates demand for parts, labour and scheduled maintenance capacity. The directive does not itself alter ownership, prices or competition rules; it imposes a mandated maintenance action and deadline for safety reasons (Applicability, Requirement, Compliance)."}},"importantCases":[],"_links":{"self":"/api/acts/ad-apu-8-garrett-apu-compressor-rotating-group","history":"/api/acts/ad-apu-8-garrett-apu-compressor-rotating-group/history","analysis":"/api/acts/ad-apu-8-garrett-apu-compressor-rotating-group/analysis","conflicts":"/api/acts/ad-apu-8-garrett-apu-compressor-rotating-group/conflicts","importantCases":"/api/acts/ad-apu-8-garrett-apu-compressor-rotating-group/important-cases","documents":"/api/acts/ad-apu-8-garrett-apu-compressor-rotating-group/documents"}}