AD/EC 120/16 Amdt 1 - Engine Controls - Twist Grip Assembly

The core concept is the twist grip assembly , the engine control mechanism on the collective lever that allows the pilot to adjust engine power by turning the grip. The AD focuses on the bonding between the drive tube and the control pinion. The drive tube transmits the pilot’s rotational input to the fuel control unit. A bonded attachment that fails under load can result in a disconnect between the twist grip and the engine, causing the engine to remain at a fixed power setting regardless of pilot input. The AD identifies non-compliant preparation of bonding surfaces as the root cause: during manufacture, the surfaces to be bonded were not prepared correctly, leading to a weakened bond that can fail over time. The concept of surface preparation is therefore the underlying technical hazard , not a design flaw in the twist grip itself, but a manufacturing quality control failure. The AD introduces the concept of identification: a letter “V” marked on the lever base indicates that the bonding has been checked or corrected. Twist grip assemblies without that “V” mark are presumptively non-compliant and must be inspected or removed. The AD also introduces a progressive compliance concept: some actions must be done within 110 flight hours or 9 months, whichever occurs first; others are effective immediately from the date of the AD. The AD also incorporates the concept of later approved revisions of the referenced service bulletins: compliance is not locked to a specific revision number; the operator may use any later revision that is approved. This gives flexibility as manufacturer data improves but also places a due diligence obligation on the operator to track revisions. The autorotation training limitation is a key concept: until the twist grip drive tube is replaced, the training must simulate a full autorotation to touchdown. This changes how flight schools teach the procedure , no power recovery is permitted until the helicopter actually lands. That changes risk profiles and syllabus timing. The AD also introduces a prohibition on installation of certain parts unless bonding strength is verified. This affects maintenance providers and parts distributors: they cannot simply return repaired assemblies to service without the necessary check. Finally, the AD supersedes an earlier EASA directive, meaning the old compliance timelines and scope are replaced; operators must check whether they were already compliant under the earlier directive and, if not, now fall under the new requirements.

This AD directly affects three categories of entities: registered owners and operators of Eurocopter (now Airbus Helicopters) EC 120 B helicopters that are fitted with any of the specified twist grip part numbers and serial numbers; maintenance organisations (both approved and self-administering) that perform work on those twist grips; and flight training organisations that conduct autorotation training in these helicopters. The applicability is limited to helicopters with RH twist grip P/N C761A2024101 with S/N 336-338, 342-353, 356-364, and 367-401 without a “V” marking; P/N C761A2024102, C761A2024103, or C761A2024104 with S/N below 418 without a “V” marking; and LH twist grip P/N C761A2025102, C761A2025103, or C761A2025104 with S/N below 382 without a “V” marking. This is a narrow population: not all EC 120 B helicopters are captured. Only those with twist grips from specific production batches are affected. The AD therefore imposes a compliance burden on a subset of the Australian EC 120 fleet. Operators must first identify whether their helicopters fall within these serial number ranges and whether a “V” is marked on the lever base. If the part is marked “V”, the AD does not apply , the bonding has already been addressed. If not, the helicopter is grounded until compliance or until the autorotation training restriction is applied. Maintenance organisations must source the relevant service bulletins (Eurocopter EC 120 SB No. 76-005 Revision 1 and ASBs 76A005 Rev 1 and 76A006 Rev 2) and perform the removal, inspection and replacement of drive tubes. They also must ensure the installation prohibition is observed when returning components to service. Flight training organisations that use affected EC 120s for autorotation training must revise their lesson plans and briefings to ensure that the manoeuvre is conducted as a full autorotation to touchdown rather than a power recovery at altitude. This has safety implications: full autorotations to touchdown carry different risk profiles (e.g., landing energy management, touchdown accuracy) compared to power-recovery practice. The AD indirectly affects parts distributors and component repair shops that handle twist grips: they may not install unmodified assemblies without the bonding strength check. The Australian Civil Aviation Safety Authority is also affected in its enforcement and surveillance role: it must verify compliance through maintenance records and operational checks. The cost of compliance falls entirely on private operators and training businesses , there is no government subsidy or compensation mentioned. The opportunity cost includes aircraft downtime for maintenance, labour for identification and removal, and the cost of replacement parts if the drive tube is found non-compliant. For a small helicopter training business, even a few weeks of downtime on one aircraft can be significant.

The AD imposes several specific duties on the helicopter owner, operator and maintenance personnel. Duty to identify: within 9 months of the effective date (18 December 2008), helicopters that have already accomplished Eurocopter EC 120 SB No. 76-005 Revision 0 must have their collective lever identified in accordance with paragraph 2.B.3 of ASB No. 76A005 Revision 1. This is a documentation task: the maintenance release must record that the lever has been checked and marked if compliant. Duty to remove drive tube: for helicopters not already compliant, the drive tube must be removed from listed RH and LH twist grip assemblies within 110 flight hours or 9 months, whichever occurs first. This is a physical maintenance action that requires the component to be taken off the aircraft and either replaced or sent for bonding strength checking. Duty to modify training: pending the drive tube replacement, any autorotation training on the affected helicopter must be carried out as a full autorotation to touchdown. The pilot-in-command or the training organisation has a duty to ensure no power recovery is attempted before the helicopter touches down. This overrides standard training syllabi that might include a power recovery at a safe altitude. Duty not to install: from the effective date, no person may install a twist grip assembly with the specified P/N and S/N (without “V” marking) on any helicopter unless the drive tube has been replaced and the collective lever marked per the ASB. This duty falls on maintenance providers, parts suppliers and operators returning aircraft to service. Duty to check bonding strength: for twist grip assemblies with S/N below 418 (RH) or below 382 (LH) that have not already accomplished SB No. 76-005 Revision 1, they may not be installed unless the bonding strength of the control pinion on both pilot and co-pilot collective lever drive tubes has been checked per paragraph 2.B.4 of ASB No. 76A006 Revision 2. This is a verification duty: a mechanical test must be performed and recorded. Right to use later revisions: the AD expressly states that the use of later approved revisions of the referenced documents is acceptable for compliance. This gives operators and maintainers the right to rely on updated manufacturer data without needing an amendment to the AD. It reduces the risk of obsolescence. Right to rely on prior compliance: if an operator can demonstrate that the required action was already accomplished before the AD effective date (e.g., under the earlier EASA AD 2006-0253), they are excused from repeating the work. The compliance deadlines state “unless previously accomplished”. This avoids double compliance cost. Right to operate with restrictions: the AD does not immediately ground the helicopter; it allows continued operation with the training limitation until the drive tube is replaced. This gives operators time to schedule maintenance without disrupting revenue entirely. However, that right is conditional on strict adherence to the training restriction , any deviation could be a breach of the AD.

The AD itself does not specify a monetary penalty amount; penalties for non-compliance with an Australian airworthiness directive arise under the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations 1998 (CASR). Generally, operating an aircraft in a manner that does not comply with an applicable airworthiness directive is a strict liability offence. For an individual, the maximum penalty in 2008 for a breach of a CASA AD would likely be up to 50 penalty units (where one penalty unit was then $110), giving a maximum of $5,500. For a body corporate, the maximum could be five times that (250 penalty units, or $27,500). However, CASR 1998 Part 42 also imposes obligations on the registered operator to ensure that the aircraft is airworthy, and failure to comply with an AD would breach that obligation, which could result in suspension or cancellation of the aircraft’s certificate of airworthiness, effectively grounding the fleet. The AD is a legally enforceable notice. CASA’s enforcement powers include issuing directions, imposing conditions, suspending certificates, and prosecuting. The AD references “EASA AD 2008-0185” and supersedes “EASA AD 2006-0253”, which were European Aviation Safety Agency directives; those are not directly enforceable in Australia, but CASA has adopted them through its own directive. The practical enforcement mechanism is through the annual or periodic maintenance inspection: the maintenance release must record compliance with all applicable ADs. If a technician signs off an AD as completed when it is not, both the technician and the operator could face liability for falsification of maintenance records. Additionally, the AD requires specific marking of the collective lever (the “V” mark). If an inspector finds an aircraft without that marking when it should have it, that is prima facie evidence of non-compliance. The AD also creates a prohibition on installation that extends to any person (not just the operator). That means a parts supplier who sells an unmodified twist grip to a repair station could be liable. The autorotation training restriction is an operational requirement; if a training organisation conducts a power recovery autorotation in an affected aircraft before the drive tube is replaced, the pilot-in-command and the organisation could be prosecuted. CASA may also take administrative action such as issuing a direction to cease training operations. The enforcement of this AD is likely to be complaint-driven or discovered during routine airworthiness audits. The background section notes that the AD is a response to an actual failure, which elevates enforcement priority. Operators should expect heightened scrutiny of twist grip bonding records.

This AD sits within a hierarchy of aviation safety regulation. It is issued by CASA under the authority of the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations 1998 (CASR). As an airworthiness directive, it takes precedence over any conflicting maintenance manual recommendations, because compliance with an AD is mandatory. The AD explicitly references Eurocopter service bulletins (SB 76-005, ASB 76A005, ASB 76A006). Those bulletins are manufacturer-issued instructions that are normally advisory, but when an AD mandates them, they become legally binding. The AD also references EASA AD 2008-0185 and notes that it supersedes EASA AD 2006-0253. That indicates a degree of harmonisation: Australian regulatory action mirrors European action on the same unsafe condition. However, the Australian AD is a stand-alone instrument; compliance with the EASA AD does not automatically constitute compliance with the CASA AD unless the CASA AD expressly accepts it. In this case, the CASA AD has slightly different compliance deadlines (110 hours / 9 months versus whatever the EASA version required). Operators who previously complied with EASA AD 2006-0253 may still need to check if they meet the updated requirement of this amendment. The AD also interacts with CASR Part 42 (Continuing Airworthiness) and Part 66 (Maintenance Personnel Licence) requirements. The person performing the drive tube removal must be authorised under CASR Part 66 or Part 145. The maintenance release must be endorsed in accordance with Part 42. If the aircraft is used for commercial air transport or aerial work, additional operational regulations under CASR Part 119 or Part 133 may apply, particularly regarding the training syllabus amendment. The autorotation training restriction interacts with the Civil Aviation Order (CAO) 29.2 or other regulatory provisions governing flight training , the AD effectively overrides any standard training procedure that permits power recovery in autorotation. For an aircraft operated under a foreign airworthiness certificate but within Australia (e.g., a visiting aircraft), the AD may still apply if the aircraft is registered in Australia or operated by an Australian operator. For foreign-registered aircraft, CASA might not directly enforce, but the operator would still need to comply with their own state’s equivalent directive. The AD does not mention any interaction with the Competition and Consumer Act 2010; but if a twist grip manufacturer or distributor misrepresented the bonding strength, that could be a separate commercial law issue. The AD does not interact with workplace health and safety laws directly, but the autorotation touchdown requirement may raise risk management obligations under state WHS Acts. Overall, this AD is a narrow instrument that overrides permissive manufacturer instructions and standard training procedures to impose mandatory safety actions.

The source text provides limited amendment history. The original AD/EC 120/16 came into effect on 26 October 2006. That original was based on the earlier EASA AD 2006-0253. The amendment before us, Amdt 1, was signed on 6 November 2008 by James Coyne, Delegate of CASA, and it becomes effective on 18 December 2008. The amendment supersedes the earlier EASA AD 2006-0253 and replaces it with EASA AD 2008-0185 (dated 8 October 2008) as the referenced European directive. The background explains that the amendment was prompted by further investigation that revealed additional twist grip batches potentially affected by non-compliant surface preparation. The original AD had a narrower scope; this amendment expands the applicability to include more serial numbers and perhaps additional part numbers. Specifically, the original AD likely covered only the RH twist grip assembly with P/N C761A2024101 and S/N listed; Amdt 1 adds LH twist grip assemblies and includes part numbers C761A2024102, C761A2024103, C761A2024104 (RH) and C761A2025102, C761A2025103, C761A2025104 (LH) with S/N thresholds. The amendment also introduces a new compliance requirement (Requirement 3) regarding bonding strength checking for certain assemblies that have not accomplished SB 76-005 Revision 1. It also adds a note specifying that later approved revisions of the documents are acceptable. The amendment history beyond this is not provided. There is no indication of further amendments (Amdt 2, 3, etc.) in the source. It is possible that subsequent amendments have been issued since 2008, but we cannot comment on that from this text. The original AD was effective for about two years before being amended. The amendment also changes the compliance deadlines: the original AD likely had different timelines; Amdt 1 introduces a 110 flight hour or 9 month deadline for drive tube removal, and a 9 month deadline for identification on previously compliant helicopters. The amendment also clarifies that for helicopters that have already accomplished SB 76-005 Rev 0, only identification is required (not removal). The background indicates that the amendment aligns the AD with the latest approved data from the manufacturer. This is a typical pattern: after an initial AD, further failures or investigation lead to a broadening of scope and more prescriptive actions. The signing authority is James Coyne, a CASA delegate, on 6 November 2008. The amendment number “Amdt 1” suggests it is the first revision of the AD, but the source does not rule out interim corrections. The effective date is 18 December 2008, giving operators approximately six weeks from the signing date to prepare for compliance.

The source text does not mention any litigation history. There are no references to court cases, civil suits, or enforcement actions flowing from this AD. This is unsurprising: airworthiness directives are regulatory instruments that are rarely litigated directly in Australia. Challenges are possible through the Administrative Appeals Tribunal (AAT) or judicial review under the Administrative Decisions (Judicial Review) Act 1977, but such challenges are uncommon and would typically succeed only if the decision was unreasonable or procedurally flawed. The AD is based on an actual failure event and has a technical foundation; courts tend to defer to CASA’s safety expertise. There is also no mention of product liability litigation between the helicopter operator and the twist grip manufacturer arising from the bonding failure. If such litigation occurred in relation to the incident that prompted the AD, it is not referenced in this source. It is possible that Eurocopter (now Airbus Helicopters) issued the service bulletins as part of a product improvement program, and any liability may have been settled privately. The AD itself does not create a private right of action; it is a public safety regulation. For a lawyer researching potential exposure, the lack of litigation history could suggest that compliance has been straightforward or that disputes are resolved through administrative channels rather than court proceedings. That said, the autorotation training restriction could theoretically lead to an accident if a pilot misjudges a forced landing during training, and that accident might give rise to negligence litigation. But again, that is not part of the AD’s litigation history. The AD’s reference to EASA ADs suggests that similar directives were in place in Europe; there may be foreign litigation regarding the same bonding issue, but that is beyond the source. In summary, from this source, there is no litigation history to report. The section can note that the AD has not been challenged in court according to the available information, but should not speculate about unreported cases.

Several aspects of this AD could catch an unwary operator or maintenance organisation. The “V” marking: the AD exempts twist grips that have a letter “V” marked on the lever base. An operator who misreads the marking or fails to check for it could unnecessarily ground the aircraft or waste resources doing work that is already done. Conversely, a deceptive or worn “V” mark might give false confidence. The AD does not specify how to verify the “V” , is it stamped, etched, painted? The maintenance procedure must confirm it is genuine. Serial number ranges: the AD uses inclusive ranges (e.g., “336 to 338 (inclusive), 342 to 353 (inclusive)”). An operator with S/N 340 is not covered; but if the part has been replaced with one from the affected range, it becomes covered. The AD does not exempt parts that were previously replaced unless the replacement part has the “V” mark. The relation between Requirements 1 and 2: If a helicopter has already accomplished SB 76-005 Rev 0, only identification is required within 9 months. But if a helicopter has not accomplished that bulletin, the operator must remove the drive tube within 110 hours / 9 months. It’s possible for an operator to think they have accomplished Rev 0 but actually accomplished only a previous revision or an informal rectification. The AD does not define what constitutes “accomplished” , presumably a logbook entry referencing the exact SB revision is required. Autorotation training restriction: This is an operational gotcha. Many training manuals allow a power recovery at a minimum altitude of 20-50 feet. The AD mandates “full autorotation until the helicopter touches down”. That changes the profile significantly: it requires the instructor to be prepared for a touchdown autorotation, which has a higher risk of hard landing or dynamic rollover if mishandled. Some training organisations might continue to do power recovery autorotations inadvertently, especially if the AD is not briefed to all instructors. The 110 flight hour deadline: that can be reached very quickly in a high-utilisation training helicopter. An operator might think they have 9 months, but if they fly 50 hours per month, they will hit 110 hours in just over two months. The AD says “whichever occurs first”, so operators must track flight hours carefully. Requirement 3 prohibits installation of entire twist grip assemblies unless bonding strength is checked. This applies even to assemblies that have not yet been installed on an aircraft. A maintenance shop that receives a used twist grip from a spare parts pool cannot install it without the check, even if the twist grip looks fine. That could delay parts availability. The AD allows later approved revisions of the service bulletins. That is a benefit, but it also means an operator must check whether a later revision exists and whether it changes the compliance method. Ignorance of a later revision could lead to non-compliance if an operator follows an outdated bulletin. The AD supersedes an earlier EASA directive: if an operator was compliant under the old directive, they must verify they also meet this amendment. The old directive might have had different scope (e.g., only RH twist grips). This amendment adds LH twist grips. An operator who only addressed the RH side under the old AD may now be non-compliant for the LH side. The signatory: The AD is signed by a delegate of CASA, not the Minister. While legally valid, some operators might question the authority. It is valid. Lastly, the AD does not specify who pays for the parts and labour. That falls on the operator. There is no compensation. For a small business, the cost of removing both RH and LH drive tubes, inspecting, potentially replacing them, and updating training programs can be significant.

Compliance with AD/EC 120/16 Amdt 1 requires a step-by-step approach tailored to the helicopter’s prior compliance state. Step 1: Determine which requirement applies. The operator should review maintenance records to determine whether the helicopter has already accomplished Eurocopter EC 120 SB No. 76-005 Revision 0. If yes, proceed with Requirement 1. If not, proceed with Requirement 2. Step 2: For Requirement 1 compliance (helicopter already accomplished Rev 0): within 9 months of 18 December 2008 (i.e., by 18 September 2009), the collective lever must be identified in accordance with paragraph 2.B.3 of ASB No. 76A005 Revision 1. This means checking that the lever base has the required marking (presumably the “V” mark) and recording it in the aircraft logbook. No drive tube removal is necessary. The maintenance release should reference the ASB and the AD. Step 3: For Requirement 2 compliance (helicopter not yet accomplished Rev 0): (a) within 110 flight hours or 9 months (whichever first), remove the drive tube from affected RH twist grip assemblies (P/N C761A2024101 with S/N 336-338, 342-353, 356-364, 367-401 without “V”; and RH assemblies P/N C761A2024103/4104 with S/N 336-338, 342-353, 356-364, 367-401 without “V”) and from LH twist grip assemblies (P/N C761A2025103/5104 with S/N 371-381 without “V”). Removal must be done per paragraph 2.B of SB No. 76-005 Revision 1. The drive tube must be inspected or replaced. (b) Pending completion of (a), any autorotation training must be conducted as a full autorotation to touchdown , no power recovery is permitted. This operational restriction must be communicated to all flight instructors and pilots. (c) from the effective date, do not install any twist grip with the listed P/N and S/N unless the drive tube has been replaced and the collective lever marked per ASB 76A005 Rev 1 paragraphs 2.B.2 and 2.B.3. Step 4: For Requirement 3 compliance (applies to RH twist grips P/N C761A2024102, 4103, 4104 with S/N below 418; and LH twist grips P/N C761A2025102, 5103, 5104 with S/N below 382 , if they have not accomplished SB 76-005 Rev 1): from the effective date, do not install such assemblies on any helicopter unless the bonding strength of the control pinion on both pilot and co-pilot collective lever drive tubes has been checked per paragraph 2.B.4 of ASB No. 76A006 Revision 2. This requires a maintenance action that may involve a pull test or other verification method. Step 5: Record compliance. Enter each action in the aircraft maintenance logbook with reference to the AD number and the specific service bulletin revision used. Keep copies of the bulletins and any test results. Step 6: Monitor flight hours for Requirement 2(a) deadline. Implement an hours tracking system to ensure the 110-hour limit is not exceeded. Step 7: Review training syllabus. If the aircraft is used for training, update the flight manual or training notes to specify that autorotation training must be to touchdown until the drive tube is replaced. Brief all instructors and check pilots. Step 8: Check for later approved revisions. The AD permits the use of later revisions of the referenced SB and ASBs. Before commencing work, verify with the manufacturer whether any later revision exists and whether it simplifies or changes the procedure. Step 9: Ensure parts traceability. When purchasing twist grips from inventory, verify that they have the “V” marking or that bonding has been checked. Do not accept parts without documentation. Step 10: Consider impact on other jurisdictions. If the aircraft operates internationally, check that the country of operation recognises CASA ADs or requires compliance with EASA AD 2008-0185. The compliance timeline may differ. The key risk is missing the 110-hour deadline or inadvertently performing power recovery autorotations. Maintaining a simple checklist and briefing sheet for pilots and maintainers will reduce the chance of error.