AD/AT/29 Amdt 1 - Engine Mount

An airworthiness directive (AD) is a legally enforceable notification issued by CASA under the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations 1998 (not cited in the source but the AD’s status implies this framework). It requires owners, operators, and maintainers of registered Australian aircraft to correct an unsafe condition or to conduct inspections to detect that condition. Non-compliance renders the aircraft unairworthy and may lead to grounding, penalties, or revocation of certificates.

The engine mount in question is the structure that attaches the engine to the airframe. Cracking in this component risks failure of the mount and possible separation of the engine from the aircraft, a catastrophic failure mode. The directive distinguishes between mounts with gussets (reinforcing brackets welded at the joint of the lower tube and the ring) and mounts without gussets. Gussets were originally installed under prior service letters as a terminating action to end repetitive inspections. However, this amendment 1 was prompted by a crack found completely through a gusset on a Model AT-602 aircraft (a model not directly covered but indicative of a generic design flaw). Accordingly, the directive eliminates the terminating action and requires inspections for all aircraft regardless of gusset presence.

Time in service (TIS) is the total accumulated operating hours of the aircraft airframe, measured from new. The directive uses TIS as the trigger for inspection intervals, creating two regimes: a low-hour regime (less than 5,000 hours for most models, less than 1,300 for AT-502A) with annual inspections, and a high-hour regime with more frequent 100-hour inspections. This reflects a fatigue-based risk model: as hours increase, crack initiation and growth become more likely, so inspection frequency increases.

Snow Engineering Co. Service Letter No. 253 Revision C is the designated inspection procedure. The directive does not reproduce the contents of the service letter; it merely references it. Operators must obtain a copy of that document and follow its methods, which are likely a combination of visual inspection and possibly dye penetrant or eddy current testing. The cost of obtaining the service letter and the labour hours required to perform the inspection are not stated but are real compliance costs.

The directive directly affects any person or organisation that operates, owns, or maintains an Airtractor model listed in the applicability table: AT-400, AT-400A, AT-402, AT-402A, AT-402B, AT-502, AT-502A, AT-502B, and AT-503A, with serial numbers 0001 through 1175 for the 400 series and 0001 through 2597 for the 500 series. This covers a substantial portion of the Australian agricultural aviation fleet, as Airtractor aircraft are widely used for crop dusting, firefighting, and aerial application. The directive affects approximately the first 1,175 of the 400 series and the first 2,597 of the 500 series built.

Indirectly, the directive affects maintenance organisations, licensed aircraft maintenance engineers (LAMEs) who perform the inspections, and suppliers of replacement engine mounts or repair kits from Air Tractor, Inc. Insurance underwriters may also adjust premiums or coverage terms based on compliance status, as unairworthy aircraft invalidate hull and liability insurance. Lessors and financiers with security interests in affected aircraft will require evidence of compliance to protect asset value.

The directive imposes no obligations on manufacturers (Air Tractor, Inc.) other than supplying repair instructions when requested. The compliance burden falls entirely on the registered operator and the maintenance entity. For operators with one or two aircraft, the cost of repetitive inspections and potential replacement mounts (which may cost tens of thousands of dollars plus labour) represents a significant operational expense. For fleet operators with many aircraft, the cumulative cost is high. The directive also creates administrative costs: maintaining logs of TIS, scheduling inspections within the specified windows, and recording results.

Because the directive applies to Australian registered aircraft only, importers and second-hand purchasers must verify compliance before taking delivery. An aircraft that has not been inspected in accordance with the directive is not airworthy and cannot be flown lawfully. This directive also affects the resale value of affected aircraft, as potential buyers will factor in the ongoing inspection burden.

The primary duty under AD/AT/29 Amdt 1 is on the registered operator to ensure that each affected aircraft is inspected at the mandated intervals and that any crack damage is rectified before further flight. The inspection must be performed in accordance with Snow Engineering Co. SL No. 253 Revision C. The operator must also keep records of each inspection, including date, TIS at inspection, results, and any corrective action taken. These records must be presented to CASA upon request.

The operator has the right to choose between two corrective actions if crack damage is found: replace the engine mount with a new unit, or repair it. However, the option to repair is conditional on obtaining repair instructions from Air Tractor, Inc. The directive does not specify whether those instructions are free or what the turnaround time is; the operator effectively relies on the manufacturer’s co-operation, which creates supply chain risk. The option to replace with a new mount is straightforward but expensive, and the directive does not prescribe a part number or approved source for the new mount.

The operator also has the right to apply for an alternative means of compliance (AMOC) with CASA, but the directive does not mention this explicitly. Under general CASA policy, an operator may propose an equivalent inspection method or reduced interval if supported by data, but such approval is at CASA’s discretion and requires time, money, and engineering justification.

The directive does not impose any obligation on the operator to retrofit gussets; in fact, it removes the earlier terminating action of installing gussets. Operators who have already installed gussets under prior service letters must continue inspecting as if the gussets were not there, because the gussets themselves have been shown to crack. This effectively renders the prior investment in gusset installation worthless in terms of reducing inspection frequency, though the gussets may still provide some structural benefit in delaying crack initiation.

The directive also creates a duty on maintenance organisations to perform the inspections competently and to document findings. If a crack is missed and later leads to an incident, the maintenance organisation may face liability for negligence.

Non-compliance with an airworthiness directive is an offence under the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations 1998. The specific penalty provisions are not recited in the directive itself, but under regulation 42ZZ of the Civil Aviation Safety Regulations, operating an aircraft that does not comply with an applicable AD may attract a penalty of up to 50 penalty units for an individual (currently around $11,000 AUD) and up to 250 penalty units for a body corporate (around $55,000 AUD), plus potential suspension or cancellation of the aircraft’s certificate of airworthiness. These figures are indicative only; the source does not provide them, but they flow from the statutory framework that empowers CASA to issue ADs.

CASA delegates are empowered to issue ADs and to enforce them. Enforcement actions include issuing a defect notice, grounding the aircraft, and requiring rectification before any further flight. Officers may conduct ramp checks and request inspection records. Repeat or deliberate non-compliance may lead to civil penalty proceedings or criminal prosecution if the conduct endangers life or property.

The directive itself does not specify a penalty for failure to inspect or repair. It states that compliance is mandatory. The background section explains that the AD is intended “to detect and correct cracks in the engine mount, which could result in failure of the engine mount and possible separation of the engine from the aircraft.” Therefore, from a safety regulation perspective, any deviation from the directive increases risk, and regulators treat such deviations seriously.

Operators should also note that insurance policies typically require compliance with all applicable ADs as a condition of coverage. Non-compliance may void cover for hull damage or third-party liability in the event of an engine mount failure. This creates a strong private incentive to comply, independent of the public penalty regime.

This directive does not exist in isolation. It is issued under CASA’s authority derived from the Civil Aviation Act 1988 (Cth) and the Civil Aviation Safety Regulations 1998 (CASR). Specifically, Part 39 of CASR (Airworthiness Directives) provides the framework for CASA to adopt or issue ADs that are mandatory. AD/AT/29 Amdt 1 is a CASA AD adopted from the corresponding FAA AD 2009-11-05, but it is tailored to the Australian regulatory context. The directive explicitly notes “FAA AD 2009-11-05 Amdt 39-15915” for cross-reference, meaning operators may also need to comply with that FAA AD if the aircraft is operated in US airspace or if the Australian AD is considered equivalent.

The directive interacts with the broader airworthiness management system under CASR Part 42 (Continuing Airworthiness) and Part 91 (General Operating and Flight Rules). For aircraft under a maintenance program, the AD must be incorporated into the operator’s schedule of inspections. A certified aircraft maintenance organisation (CAMO) is responsible for ensuring that all applicable ADs are tracked and complied with. Failure to do so can result in non-compliance by the CAMO as well as the operator.

The directive also interacts with the manufacturer’s service information. Snow Engineering Co. SL No. 253 Revision C is a proprietary document; the operator must purchase or otherwise obtain it. The directive does not incorporate the service letter by content, so the operator must adhere to the letter’s precise procedures. If the service letter itself changes or is superseded, the AD may not automatically adopt the new version; the operator would need to check for amendments to the AD or apply for an AMOC.

The directive does not conflict with privacy or competition laws, but it does impose an obligation that overrides any contractual arrangement. For example, a lease agreement that attempts to allocate compliance responsibility away from the lessor may still leave the registered operator liable to CASA. Similarly, a sale agreement that warrants the aircraft as being in compliance with all ADs as of a certain date does not relieve the new operator of performing the first inspection at the required interval.

Because the directive references an FAA AD, operators with mixed fleet or operations in the US must also satisfy the FAA’s enforcement regime. The interaction between FAA and CASA ADs can be complex; generally, CASA recognises FAA ADs as equivalent when adopted, but differences in wording or compliance times may require careful cross-checking.

The source document is AD/AT/29 Amdt 1, which amends the earlier AD/AT/29 that was itself based on FAA AD 2008-10-12. The background section reveals a chain of events. Initially, FAA AD 2007-13-17 applied to Models AT-602, AT-802, and AT-802A but not to the 400 and 500 series. After a report of a cracked engine mount on a Model AT-502B, Air Tractor developed gussets as a terminating action. This led to FAA AD 2008-10-12, which incorporated mandatory inspections for the 400 and 500 series and allowed installation of gussets to terminate repetitive inspections. CASA adopted that as AD/AT/29.

Then, a subsequent report of a crack completely through the gusset on a Model AT-602 (a model not covered by the earlier directive but indicative of a generic problem) caused the FAA to revise its opinion. The gusset, intended to be a permanent fix, was itself cracking. This prompted FAA AD 2009-11-05, which removed the terminating action and required repetitive inspections on all aircraft, with or without gussets. CASA accordingly issued Amendment 1 to AD/AT/29, effective 30 July 2009.

Thus, the amendment history is: AD/AT/29 (original) - no date given in the source; AD/AT/29 Amdt 1 - effective 30 July 2009. The source also notes that the background references the earlier FAA ADs but does not provide any further amendments after 2009. It is possible that later amendments exist, but they are not part of this instrument. Operators must check the current CASA AD register for any superseding directives.

The amendment history illustrates a common regulatory pattern: initial inspection with a terminating action, followed by discovery that the terminating action is inadequate, then reversion to indefinite repetitive inspection. This pattern imposes compliance costs that escalate over time as the regulatory knowledge of the failure mode improves but the burden is never removed. The amendment also demonstrates that regulatory reliance on manufacturer-designed fixes can be undermined by further incident reports.

The source document does not mention any litigation. Airworthiness directives are rarely litigated directly, as operators typically comply rather than challenge the safety rationale. However, the source’s reference to the background incidents (cracked engine mount on AT-502B, cracked gusset on AT-602) could form the basis for product liability claims against Air Tractor, Inc. or component manufacturers. Those claims would be separate from the AD itself.

In Australia, a court challenge to an AD could be brought on the grounds of jurisdictional error (if CASA exceeded its delegated authority) or procedural unfairness (if the operator was not given an opportunity to comment). But because ADs are issued for immediate safety reasons, courts usually defer to the regulator’s technical judgment. No known Australian case has invalidated an AD on economic grounds. The directive’s requirement to “contact Air Tractor, Inc. for repair instructions” may give rise to contractual disputes if the manufacturer refuses to provide instructions or charges exorbitant fees, but again, those disputes are not part of the AD’s litigation history.

Operators who suffer loss due to an engine mount failure after complying with the directive may have a claim against the manufacturer for defective design. Conversely, an operator who fails to comply and suffers a loss may find insurance denied. These potential legal disputes are not litigation history of the AD itself.

In summary, there is no litigation history directly arising from AD/AT/29 Amdt 1. The directive is a mandatory administrative instrument, and compliance is the norm.

Several details in the directive can catch operators off guard. First, the compliance times use multiple reference dates: “3 July 2008” appears for some initial inspections (Model AT-502A), “30 July 2009” for others, and “the last inspection performed” for repetitive inspections after 5,000 hours. These dates are not the same as the effective date of the amendment. An operator who reads only the effective date (30 July 2009) might miss that the initial compliance for some aircraft was already triggered a year earlier by the previous AD. The directive imposes an initial inspection “within the next 12 months after 3 July 2008” for AT-502A with gussets, meaning that by the time the amendment takes effect, that inspection may already be overdue.

Second, the distinction between “with gussets” and “without gussets” is critical. Many operators may have installed gussets in good faith under the earlier directive expecting to end inspections. This amendment removes that benefit. Those operators must start inspecting again immediately, regardless of whether they have installed gussets. The investment in gusset installation becomes a sunk cost with no regulatory return.

Third, the Model AT-502A has a different initial threshold (1,300 hours TIS) compared to other models (5,000 hours). An operator with an AT-502A that has not yet reached 1,300 hours TIS might mistakenly apply the 12-month rule and delay the inspection, only to trigger a breach when the hours accumulate faster than expected. The directive says “initially, upon accumulating 1,300 hours time in service or within the next 100 hours time in service after 3 July 2008, whichever occurs later.” This requires constant tracking of TIS against a fixed calendar date.

Fourth, the repetitive inspection interval for aircraft with 5,000 hours TIS or more is “not to exceed 100 hours time in service.” There is no calendar limit; the inspection is purely hour-based. An aircraft that flies 200 hours per year would need two inspections per year. One that flies only 50 hours per year would need an inspection every two years. This hour-based regime can lead to gaps if the aircraft is flown intermittently, and operators must schedule inspections within a narrow window (10 hours TIS after the threshold or 100 hours TIS from the last inspection). Missing that window by even one hour makes the aircraft non-compliant.

Fifth, the directive does not specify who performs the inspection. It says “inspect the engine mount in accordance with Snow Engineering Co. SL No. 253 Revision C.” Under CASR, only an appropriately licensed aircraft maintenance engineer (LAME) may perform such inspections, and the inspection might require specific tooling or training that not all engineers have. Operators may need to engage specialist organisations.

Sixth, the directive requires contacting Air Tractor, Inc. for repair instructions if a crack is found. There is no guarantee of a timely response; Air Tractor is a US company and may not prioritise Australian operators. The repair instructions themselves may involve welded repairs that require further non-destructive testing, adding cost and downtime.

Compliance with AD/AT/29 Amdt 1 requires a systematic approach. The registered operator must first identify whether each aircraft in the fleet is within the applicability range (model and serial number). If the aircraft is listed, the operator must determine its current TIS and whether it has gussets installed (based on maintenance records). That determines which sub-paragraph of the requirement applies.

The operator must obtain a copy of Snow Engineering Co. Service Letter No. 253 Revision C, dated 17 April 2008. This is a proprietary document; the operator should contact Snow Engineering Co. or an authorised distributor for purchase. The service letter contains the detailed inspection procedure. The operator should incorporate that procedure into the aircraft’s approved maintenance schedule.

Next, the operator must schedule the initial inspection in accordance with the compliance table. For most models, the initial inspection for aircraft with less than 5,000 hours TIS is within 12 months after 30 July 2009. But for AT-502A, the initial inspection for mounts without gussets and less than 1,300 hours is at 1,300 hours or within 100 hours after 3 July 2008, whichever is later. The operator must calculate the exact due date for each aircraft, accounting for any previous inspections performed under the earlier AD/AT/29.

During the inspection, a LAME must follow the service letter and document the results: date, TIS, findings (no crack, crack found, etc.), and any corrective action. If no crack is found, the aircraft is returned to service and the next inspection is scheduled. For aircraft with less than 5,000 hours TIS, the next inspection is within 12 months; for aircraft with 5,000 hours or more, within 100 hours TIS. For AT-502A, the interval after initial is 300 hours until 5,000 hours, then 100 hours.

If a crack is detected, the operator must ground the aircraft and choose replacement or repair. Replacement requires ordering a new engine mount from Air Tractor, Inc. or an approved supplier. Repair requires contacting Air Tractor, Inc. for instructions. The operator should keep a record of that contact and the instructions received. After either action, the aircraft may be returned to service, but the inspection regime continues: the aircraft remains subject to repetitive inspections at the intervals prescribed for its current TIS. The repair or replacement does not reset the compliance clock; it only corrects the immediate crack.

Finally, the operator must maintain a compliance log that tracks TIS accumulation, inspection due dates, inspection results, and any corrective actions. This log must be retained for the life of the aircraft and produced to CASA on request. The operator should also periodically check CASA’s website for any superseding directives, as this amendment may itself be updated or replaced.