{"id":"F2009L01575","name":"AD/AB139/8 - Generator Control Unit","slug":"ad-ab139-8-generator-control-unit","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":78321,"registerId":"commonwealth-F2009L01575-current","compilationNumber":null,"startDate":"2026-04-02","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Agusta AB139 and AW139 Series Helicopter","sectionType":"division","heading":"Agusta AB139 and AW139 Series Helicopters","content":"### Agusta AB139 and AW139 Series Helicopters\n\n| AD/AB139/8 | Generator Control Unit | 5/2009 |\n| ---------- | ---------------------- | ------ |\n\n| Applicability: | All AB139 and AW139 helicopters, all serial numbers (S/N) except for S/N 31002 to S/N 31004 and S/N 31007.                                                                                                                                                                                                                                                                |\n| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement:   | 1. Remove the number 1 and 2 generator control unit (GCU) part number (P/N) 1152550-3 and replace with GCU P/N 1152550-5 or, as an alternative, with two generator control units P/N 1152550-4, in accordance with the instructions of Agusta Bollettino Tecnico 139-133 dated 20 February 2009 or later revision approved by the European Aviation Safety Agency (EASA). |\n|                | The two installed GCUs must have the same P/N at all times (ie two P/N 1152550-4 or two P/N 1152550-5).                                                                                                                                                                                                                                                                   |\n|                | 2. GCUs P/N 1152550-3 may not be installed as a replacement spare on any helicopter.                                                                                                                                                                                                                                                                                      |\n|                | Note: EASA AD 2009-0042 refers.                                                                                                                                                                                                                                                                                                                                           |\n| Compliance:    | For Requirement 1 - Within six months after the effective date of this Directive.                                                                                                                                                                                                                                                                                         |\n|                | For Requirement 2 - After the effective date of this Directive.                                                                                                                                                                                                                                                                                                           |\n|                | This Airworthiness Directive becomes effective on 7 May 2009.                                                                                                                                                                                                                                                                                                             |\n| Background:    | EASA has advised that laboratory tests performed on a new a GCU model under development have shown a potential fault in the overvoltage protection of the currently installed generator control units P/N 1152550-3. This condition, if not corrected, could adversely affect the electrical power generation and distribution system functionalities.                    |\n\n![](image.001.png)  \nJames Coyne  \nDelegate of the Civil Aviation Safety Authority\n\n27 March 2009","sortOrder":0},{"sectionNumber":"AD/AB139/8","sectionType":"part","heading":"AD/AB139/8","content":"## AD/AB139/8","sortOrder":1},{"sectionNumber":"Generator Control Unit","sectionType":"part","heading":"Generator Control Unit","content":"## Generator Control Unit","sortOrder":2},{"sectionNumber":"5/2009","sectionType":"part","heading":"5/2009","content":"## 5/2009","sortOrder":3}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The Directive implements a targeted safety measure addressing a GCU overvoltage‑protection fault identified by EASA. It confines obligations to specified AB139/AW139 serial numbers, mandates replacement options and a ban on the old part as spare, and sets a six‑month compliance period. There is no indication in the text that the Directive expands beyond that specific technical corrective action or the fleet portion identified."},"complexity_factors":["Targeted technical fix limited to a single component type (GCU P/N 1152550‑3) — lowers legal complexity but requires technical compliance (Requirement).","Applicability exceptions for specific serial numbers (S/N 31002–31004 and 31007) — requires fleet-level record checks to confirm applicability (Applicability).","Alternative compliance options: either two P/N 1152550‑4 units or two P/N 1152550‑5 units, plus a requirement that both installed GCUs share the same P/N — adds procurement and configuration constraints (Requirement).","Prohibition on installing the old part as a spare — creates a parts‑management and logistics burden for operators and suppliers (Requirement 2).","Mandated method: actions must follow Agusta Bollettino Tecnico 139‑133 or later EASA‑approved revision — introduces dependency on manufacturer instructions and regulator approval for acceptable procedures (Requirement).","Short compliance window (six months from effective date) — increases scheduling pressure on maintenance planning and parts sourcing (Compliance).","Safety risk described (overvoltage protection fault) is technical and specific — requires verification/testing during replacement to ensure fault mitigation (Background).","Regulatory cross‑reference to EASA AD 2009‑0042 — necessitates coordination/consistency checks between CASA guidance and EASA documents (Note)."],"plain_english_summary":"This Directive requires owners/operators of Agusta AB139 and AW139 helicopters (except S/N 31002–31004 and 31007) to remove generator control units P/N 1152550‑3 and replace them with either two P/N 1152550‑4 units or two P/N 1152550‑5 units (both GCUs must match). It also bans installing P/N 1152550‑3 as replacement spares. Compliance is required within six months (effective 7 May 2009). EASA laboratory tests identified a potential GCU overvoltage‑protection fault that could affect electrical power generation and distribution."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a standard, narrow Airworthiness Directive addressing a specific identified safety defect in a specific aircraft type. The scope remains tightly focused on the generator control unit replacement requirement as originally intended."},"complexity_factors":["Very short document (approximately 250 words)","Only 3 defined part numbers (P/N 1152550-3, 1152550-4, 1152550-5)","Simple two-part requirement structure with clear compliance deadlines","Single cross-reference to EASA AD 2009-0042 (background only)","No nested exceptions or conditional logic — only one straightforward applicability exclusion (specific serial numbers)","Plain language background explanation included"],"plain_english_summary":"Owners and operators of Agusta AB139 and AW139 helicopters (except serials 31002–31004 and 31007) must replace the faulty generator control units (GCU P/N 1152550-3) within six months with two identical new units (P/N 1152550-5 or 1152550-4). The old part is immediately banned as a spare. This mandatory AD addresses an overvoltage‑protection fault that risks electrical-system failure and loss of critical systems in flight."},"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-ab139-8-generator-control-unit","history":"/api/acts/ad-ab139-8-generator-control-unit/history","analysis":"/api/acts/ad-ab139-8-generator-control-unit/analysis","conflicts":"/api/acts/ad-ab139-8-generator-control-unit/conflicts","importantCases":"/api/acts/ad-ab139-8-generator-control-unit/important-cases","documents":"/api/acts/ad-ab139-8-generator-control-unit/documents"}}