{"id":"F2008L03494","name":"AD/EC 135/20 - Main Transmission Mast Bearing Retainer Bolts","slug":"ad-ec-135-20-main-transmission-mast-bearing-retainer-bolts","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":120559,"registerId":"commonwealth-F2008L03494-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"Eurocopter EC 135 Series Helicopters","sectionType":"division","heading":"Eurocopter EC 135 Series Helicopters","content":"### Eurocopter EC 135 Series Helicopters\n\n| AD/EC 135/20 | Main Transmission Mast Bearing Retainer Bolts | 12/2008 TX |\n| ------------ | --------------------------------------------- | ---------- |\n\n| Applicability: | Eurocopter Deutschland GmbH (ECD) EC 135 P1(CDS), EC 135 P1(CPDS),EC 135 P2(CPDS), EC 135 P2+, EC 135 T1(CDS), EC 135 T1(CPDS),EC 135 T2(CPDS) and EC 135 T2+ helicopters. |\n| -------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n| Requirement: | 1. Inspect the attachment hardware and install locking washers in accordance with Section 3.B of ECD Alert Service Bulletin (ASB) No. EC135-63A-013Revision 02.2. Unless accomplished as required by Requirement 1 of this AD, inspect the attachment hardware and install locking washers in accordance with Section 3.B of ECD ASB No. EC135-63A-013 Revision 02.3. For helicopters that have already been modified, prior to the effective date of this AD, in accordance with ECD ASB No. EC135-63A-013 at original issue or Revision 01; inspect the attachment hardware and install locking washers in accordance with Section 3.B of ECD ASB No. EC135-63A-013 Revision 02.4. Do not install a main transmission on a helicopter, unless it has been modified in accordance with Section 3.B of ECD ASB No. EC135-63A-013 Revision 02.The use of later approved revisions of this document is acceptable for compliance with the requirements of this AD.Note: EASA Emergency AD 2008-0175-E dated 16 September 2008 refers. |\n| Compliance: | For Requirement 1 - After the effective date of this AD, when unusual vibrations are detected during the start or the end phase of the main rotor’s running, within 3 flight cycles after detection.For Requirement 2 - Within the next 50 flight hours (FH) after the effective date of this AD, but not later than 31 March 2009.For Requirement 3 - Within 400 FH (+/- 10%) after the effective date of this AD.For Requirement 4 - From the effective date of this AD. |\n| | This Airworthiness Directive becomes effective on 22 September 2008. |\n\n| Background: | One operator has reported the occurrence of unusual vibrations during the start phase of the main rotor on one helicopter. These vibrations stopped after the application of torque. The troubleshooting accomplished by the maintenance personnel showed that six of the eight attachment screws of the lower hub-shaft bearing support had loosened. After inspection of the affected operator’s fleet, the attachments screws of the lower hub-shaft bearing support were found loosened on the main transmissions of two additional helicopters. The lower hub-shaft bearing consists of a ball bearing and a roller bearing. The outer race of the roller bearing is fixed to the housing with screws. Should all attachment screws become loose, the outer race of the roller bearing might separate, which would constitute an unsafe condition. In such case, however, the axial guidance of the rotor hub-shaft would still be ensured.For the reasons described above, this AD requires the inspection of the main transmission attachment hardware and installation of locking washers. |\n| ----------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |\n\n![](image.001.png) \nCharles Lenarcic \nDelegate of the Civil Aviation Safety Authority\n\n17 September 2008","sortOrder":0},{"sectionNumber":"AD/EC 135/20","sectionType":"part","heading":"AD/EC 135/20","content":"## AD/EC 135/20","sortOrder":1},{"sectionNumber":"Main Transmission Mast Bearing Retainer ","sectionType":"part","heading":"Main Transmission Mast Bearing Retainer Bolts","content":"## Main Transmission Mast Bearing Retainer Bolts","sortOrder":2},{"sectionNumber":"12/2008 TX","sectionType":"part","heading":"12/2008 TX","content":"## 12/2008 TX","sortOrder":3}],"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 appears focused and targeted on its original safety purpose. It addresses a specific mechanical defect (loose bearing retainer bolts) in a defined aircraft type with clear inspection and modification requirements. There is no evidence of scope creep beyond the original safety intent."},"complexity_factors":["Multiple compliance pathways with different deadlines depending on aircraft modification history and whether symptoms are detected","Four distinct requirements with different timing triggers (symptom-driven vs. calendar/flight-hour based)","Cross-reference to external technical document (Eurocopter Alert Service Bulletin EC135-63A-013) with multiple acceptable revisions","Nested conditional logic: Requirement 2 only applies 'unless accomplished as required by Requirement 1'; Requirement 3 applies only to previously modified helicopters","Specific flight hour tolerances (+/- 10%) mentioned for one compliance window","Reference to EASA (European) Emergency AD for additional context"],"plain_english_summary":"This CASA Airworthiness Directive mandates inspections and corrective action on certain Eurocopter EC135 (P/T series) main transmissions after reports of loose attachment bolts on the lower hub‑shaft bearing support. Owners, operators and maintenance personnel must follow the manufacturer’s service bulletin to inspect and install locking washers to prevent bolt loosening. Compliance is urgent — immediate checks are required if unusual vibrations occur, with defined short-term deadlines for remaining fleets."},"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The AD's scope aligns with the stated safety objective in the text: it targets specified EC135 variants and mandates inspection and installation of locking washers per the cited Alert Service Bulletin to address loosened attachment screws and potential roller-bearing outer race separation. It also explicitly covers helicopters previously modified under earlier ASB versions and restricts installation of unmodified main transmissions, so it does not expand beyond that identified fleet or those corrective measures (see 'Applicability' and 'Requirement')."},"complexity_factors":["Multiple conditional compliance triggers and timeframes (e.g. 'within 3 flight cycles after detection' for Requirement 1; 'within 50 FH but not later than 31 March 2009' for Requirement 2; 'within 400 FH (+/- 10%)' for Requirement 3) — see 'Compliance'.","Reference to several specific revisions of ECD Alert Service Bulletin No. EC135-63A-013 (Revision 02.2, 02.3, 02.4, original issue/Revision 01) and acceptance of later approved revisions — see 'Requirement'.","Different actions depending on whether helicopters were previously modified before the AD's effective date — see 'Requirement' (paragraph about helicopters already modified).","Prohibition on installing a main transmission unless modified per Section 3.B of the ASB, creating an ongoing compliance obligation for maintenance and parts installation — see 'Requirement'.","Applicability limited to a defined set of EC135 submodels, requiring operators to determine whether their airframes fall within scope — see 'Applicability'.","Implementation requires access to and execution of procedures in the referenced ASB (Section 3.B), so compliance depends on availability of that service information and maintenance capability — see 'Requirement'.","Cross-reference to EASA Emergency AD 2008-0175-E introduces an external regulatory linkage to interpretive material — see note in 'Requirement'."],"plain_english_summary":"This Airworthiness Directive requires operators of specified Eurocopter EC135 variants to inspect main transmission mast bearing attachment hardware and install locking washers according to the cited Eurocopter Alert Service Bulletin. It applies when unusual main-rotor vibrations occur or within specified flight-hour windows, and prevents possible separation of the roller-bearing outer race that could follow loose attachment screws; operators and maintenance organisations must carry out the inspections and modifications to comply."}},"importantCases":[],"_links":{"self":"/api/acts/ad-ec-135-20-main-transmission-mast-bearing-retainer-bolts","history":"/api/acts/ad-ec-135-20-main-transmission-mast-bearing-retainer-bolts/history","analysis":"/api/acts/ad-ec-135-20-main-transmission-mast-bearing-retainer-bolts/analysis","conflicts":"/api/acts/ad-ec-135-20-main-transmission-mast-bearing-retainer-bolts/conflicts","importantCases":"/api/acts/ad-ec-135-20-main-transmission-mast-bearing-retainer-bolts/important-cases","documents":"/api/acts/ad-ec-135-20-main-transmission-mast-bearing-retainer-bolts/documents"}}