The central concept is the engine mount member, which refers to the tubular steel components that form the structure attaching the engine to the airframe. The AD particularly focuses on the upper left and right hand members, where failures have occurred. Internal corrosion is the deterioration from the inside of these tubes, often caused by moisture or water ingress, leading to rust that reduces wall thickness and can cause sudden structural failure. Pin holing describes small perforations that may be visible on the surface as a result of advanced internal corrosion. The inspection method uses probing with an ice pick or equivalent tool: a sharp instrument is gently pressed into the metal surface to detect weak spots or holes. If the member appears solid, the next step is to drill a No. 37 size hole (approximately 0.104 inch diameter) at both the upper and lower ends. This allows direct visual and tactile inspection of the interior for rust, water, or sludge. Slushing compound (Lionoil or equivalent) is a corrosion-inhibiting oil used to coat the interior of the tubes after inspection; it is poured in, swished around, then drained out, leaving a protective film. Drive screws (AN 535-4-3) are used to plug the drilled holes permanently. The replacement member must meet a precise specification: 7/8 inch outer diameter, 0.035 inch wall thickness, made of 4130 chromium-molybdenum steel, heat treated to achieve a yield strength of 85,000 pounds per square inch. The AD introduces a subjective judgment standard at Note 1: “No exact method exists in the field for measuring the wall thickness remaining … but a close visual inspection of the drilled hole coupled with the condition encountered … will allow a reasonable judgment.” This means the inspector bears significant discretion in deciding whether a member is sufficiently sound or must be replaced. The AD also adopts the concept of source document: FAA AD 64-05-06, which is the origin of the requirements. The commencement date of 17 September 2020 is the trigger for the initial compliance period. The recurrence interval (100 hours or 12 months) is a classic airworthiness maintenance schedule concept. The directive only applies to GC-1B aircraft with standard engine mount Part Number 11-710-2520; aircraft with a different engine mount part number are not subject. This narrows the affected fleet considerably.

The primary affected parties are the owners and operators of Australian registered Swift Museum Foundation GC-1B model aeroplanes fitted with engine mount part number 11-710-2520. Because the AD is mandatory, these individuals or entities bear the cost and logistical burden of performing the inspection and any necessary replacement within the prescribed intervals. Maintenance organisations (both certificated repair stations and licensed aircraft maintenance engineers) are affected because they must carry out the inspection and replacement work in accordance with the AD’s detailed procedures. They must also understand the subjective judgment allowed by Note 1 and be prepared to defend their decisions in the event of an audit or dispute. Sellers and buyers of GC-1B aircraft are indirectly affected: a seller may need to demonstrate compliance with the AD to complete a sale, and a buyer may factor the recurring maintenance cost into the purchase decision. Insurers underwriting hull or liability coverage may require evidence that the AD is complied with, or may adjust premiums or exclude coverage for non-compliant aircraft. The AD does not affect GC-1A model aircraft or GC-1B aircraft with a different engine mount part number. According to the background, the Australian Aircraft Register showed that GC-1B aircraft had been registered for some time; the number of affected aircraft is likely small, but the cost per aircraft may be non-trivial because the inspection involves drilling holes into the structure and potentially welding in new members, which requires specialised skills and possibly removal of the engine. The recurrent nature of the compliance (every 100 hours or 12 months) means the burden is ongoing, not a one-off. For an owner who flies infrequently, the annual interval will drive the compliance cycle. The AD also imposes a burden on CASA itself, which must enforce compliance and may need to respond to requests for alternative means of compliance or interpretations. The directive does not explicitly allow for alternative methods, but under the Civil Aviation Safety Regulations, CASA can approve deviations if an equivalent level of safety is demonstrated.

The central duty is to inspect the engine mount members in accordance with the AD’s requirements. This duty is triggered on the commencement date of 17 September 2020, with an initial compliance window of six months, and then recurs at each 100 hours time in service or every 12 months, whichever comes first. The duty includes probing each member with an ice pick or equivalent, drilling No. 37 holes at the upper and lower ends of members that appear solid, and inspecting for rust, water, or deterioration. If any member is found to be damaged from internal corrosion, the duty is to replace it with a new member meeting the specified material and heat treatment, weld it in place, fill the member with Lionoil or equivalent slushing compound, drain it, and plug the holes with drive screws AN 535-4-3. The duty extends to members that are not damaged: even sound members must have the slushing compound treatment and plugging. There is a right to use equivalent tools (ice pick “or equivalent tool”) and equivalent slushing compounds (Lionoil “or equivalent slushing compound”). The AD does not define what constitutes an equivalent compound or tool, leaving that to the engineer’s judgment, subject to CASA’s overarching authority. The operator has a right to rely on Note 1’s acknowledgment that no exact field method exists for measuring wall thickness; the inspector may use close visual inspection and the condition of the drilled hole to form a reasonable judgment. This creates a defence of sorts if a member later fails despite passing inspection, provided the judgment was reasonable based on the information available at the time. The operator also has a right to document prior accomplishment: the AD says “Unless previously accomplished, within 6 months after the commencement date.” If the required actions have already been performed on the aircraft before 17 September 2020, the initial compliance is satisfied, and the recurrent interval should then run from that earlier accomplishment. However, the AD does not detail what qualifies as “previously accomplished.” It likely refers to having performed the exact procedures described, or equivalent procedures under FAA AD 64-05-06. The operator also has a right to seek an alternative means of compliance from CASA, though the AD does not mention this explicitly; such a right arises under the broader regulatory framework (Civil Aviation Safety Regulations, Part 39). No right to dispute the AD itself is provided within the directive, but judicial review under administrative law is theoretically available.

The AD itself does not specify penalties, but non-compliance with an airworthiness directive is a breach of the Civil Aviation Act 1988 and the Civil Aviation Safety Regulations 1998. Specifically, operating an aircraft that does not comply with an applicable AD is likely an offence under regulation 42.035 (continuing airworthiness obligations) or similar provisions. Penalties can include infringement notices (on-the-spot fines) or prosecution with potential court-imposed fines. For serious breaches, CASA may suspend or cancel the aircraft’s certificate of airworthiness, effectively grounding the aircraft. The aircraft’s airworthiness release or maintenance release will not be valid unless the AD is complied with and recorded. Insurance policies may also void coverage for losses arising from non-compliance. The practical enforcement mechanism is that a pilot or owner who flies the aircraft without complying with the AD risks enforcement action, and a maintenance engineer who certifies the aircraft as airworthy without the AD being done may face disciplinary action or loss of licence privileges. The AD is a mandatory directive, not a recommendation. The background notes that failures have occurred, implying that non-compliance could lead to engine separation, which would be catastrophic. CASA’s delegate signed the directive on 25 August 2020, meaning it has legal force under the Civil Aviation Act. The AD is not a guidance document; it is a regulatory instrument. The directive states that “This AD commences on 17 September 2020.” From that date, the aircraft cannot lawfully be flown beyond the initial six‑month grace period unless the inspection has been performed. After the initial inspection, the recurrent interval means the aircraft must never exceed 100 hours or 12 months since the last inspection. If the interval is missed, the aircraft is not airworthy until the inspection is done. The AD does not provide any extension or exemption mechanism within its text; any relief would need to be sought from CASA separately. The costs of non-compliance are not limited to fines: if an engine mount fails and causes damage or injury, the operator could face civil liability for negligence or breach of statutory duty.

AD/GC-1/6 sits within the hierarchy of Australian aviation law. It is issued under the Civil Aviation Act 1988 and is enforceable as a legislative instrument. It interacts with the broader continuing airworthiness framework established by Part 42 of the Civil Aviation Safety Regulations 1998 (CASR), which requires that all maintenance, including compliance with airworthiness directives, be recorded in the aircraft’s maintenance records. The AD also references FAA AD 64-05-06 as its source document. Although it adopts equivalent requirements, it is a separate Australian directive. An operator who has already complied with the FAA AD on an Australian registered aircraft before 17 September 2020 may argue that is “previously accomplished”, but the AD does not explicitly recognise FAA compliance as a substitute for its own. Because the FAA AD has not previously been mandated in Australia, CASA considered it necessary to issue a local AD. The directive applies in addition to any other airworthiness requirements for the aircraft type. For example, if the aircraft has other ADs for the engine mount, airframe, or engine, those remain in force. The AD does not override the manufacturer’s maintenance manual, but it adds a specific inspection and treatment regimen that may differ from or supplement the manual. The slushing compound requirement, for instance, is not a typical maintenance item. The AD may also interact with Work Health and Safety laws when maintenance engineers are drilling, welding, or handling chemicals. Engineers must comply with hazardous substance regulations when using Lionoil or equivalents. The directive does not address privacy or data law - none of the information required is personal. It does not conflict with trade practices law, except that any claim of “equivalent” slushing compound must be honest and not misleading. If the AD creates a monopoly for Lionoil (by naming it), that may raise competition concerns, but the allowance for “equivalent” compounds mitigates that. For insurance, compliance with the AD is likely a condition of policy validity; non-compliance may void cover under aviation hull and liability policies. For tax, the cost of inspection and replacement is likely deductible as a maintenance expense. The AD does not create any new rights for third parties; it is purely a regulatory safety measure.

The document presented is the original and only version of AD/GC-1/6. It was signed on 25 August 2020 by Pieter van Dijk, Delegate of the Civil Aviation Safety Authority, and it commences on 17 September 2020. The AD number (AD/GC-1/6) and the serial number 18/2020 indicate it is the sixth directive issued for this aircraft type series, and it was the 18th AD issued overall in 2020. The AD does not reference any prior amendments to itself; it appears to be a new directive. The background states that an audit found that equivalent FAA ADs had not previously been mandated in Australia. This implies that no previous Australian AD had covered the same issue. There is no mention of a draft, pre‑notice, or consultation process. The AD does not incorporate any exemptions, extensions, or later revisions. The compliance requirement is expressed as a single timeline with a one‑time initial compliance and recurrent intervals. There is no sunset clause or expiry date. The AD will remain in effect until it is either superseded by another AD or explicitly cancelled. Given that the underlying FAA AD dates from 1964, it is likely that the Australian AD will continue indefinitely unless a design change or improved inspection method renders it unnecessary. The AD also reproduces a drawing of the engine mount (image.001.jpeg), which is part of the original instrument. No amendment history is provided within the source itself; therefore, the only history is the issuance.

The source document does not mention any litigation, enforcement actions, or court decisions related to AD/GC-1/6. There is no reference to any dispute about its validity, interpretation, or application. The AD was issued in August 2020, and as of the knowledge cut‑off, there is no reported litigation. However, the underlying issue - internal corrosion of engine mounts - has presumably been the subject of accident investigations or technical studies. The AD itself states that there have been “instances of failure through internal corrosion” but does not identify any specific accidents, court cases, or legal proceedings. In the broader legal context, airworthiness directives are legislative instruments that can be challenged on administrative law grounds (e.g., unreasonableness, procedural error, ultra vires) but such challenges are rare. If an operator suffered damage because a member failed despite compliance with the AD, they might bring a claim against the manufacturer or CASA, but no such case is recorded here. The FAA AD 64-05-06, on which this AD is based, has been in force in the United States since 1964 and may have generated litigation there, but that is not mentioned. For the Australian practitioner, the absence of litigation does not mean the AD is uncontroversial; it may simply reflect the small fleet size and the fact that most owners comply. The AD’s subjective inspection standard (Note 1) could be a source of future disputes - for example, if one engineer condemns a member and another does not, or if a later failure occurs after a member was judged sound. Those disputes would likely be technical rather than legal, unless they lead to enforcement or liability claims. As of the date of the source, there is no litigation history to report.

Several aspects of AD/GC-1/6 could trap an unwary owner or engineer. First, the AD applies only to GC-1B aircraft with engine mount part number 11-710-2520. A careless owner of a GC-1A, or a GC-1B with a different engine mount (e.g., modified or replaced), might assume the AD applies and perform unnecessary work, or incorrectly record compliance for an aircraft that is not covered. Conversely, an owner of an affected aircraft with a mis‑identified part number might miss the AD. Second, the inspection method is destructive in nature: drilling No. 37 holes into the engine mount members. Although the holes are later plugged, the act of drilling introduces stress risers and potential corrosion sites. The AD assumes the plugging with drive screws will seal the hole, but any moisture ingress around the plug could create new corrosion. Third, the judgment of “damaged from internal corrosion” at Note 1 is subjective. An inspector might condemn a member that another inspector would pass, leading to unnecessary replacement cost. Conversely, a member that looks borderline might be passed and later fail. The AD explicitly states there is “no exact method” for measuring wall thickness, so the risk of either false positives or false negatives rests on the inspector’s experience and caution. Fourth, the slushing compound treatment is required even for new replacement members. Filling and draining a newly welded member adds time and cost. The compound may not be readily available in Australia; “Lionoil” is a specific product, and locating an equivalent may require research and CASA acceptance. Fifth, the recurrent interval is the earlier of 100 hours or 12 months. For an aircraft that flies very little, the annual inspection will govern. If an owner forgets the annual deadline, the aircraft is non‑airworthy even if it has flown only a few hours. Sixth, the AD does not specify record-keeping requirements beyond normal maintenance logbooks. An owner must ensure that the AD is explicitly referenced, with the date, hours at compliance, and the condition of each member evaluated. If a member is replaced, the part number and weld inspection should also be recorded. A lack of clear records may lead to disputes during a sale or audit. Seventh, the AD is based on FAA AD 64‑05‑06, which is over 50 years old. The metallurgy of 4130 steel heat treatment and welding techniques have evolved. The AD does not permit alternative materials such as 4140 or modern corrosion‑resistant alloys. Eighth, the drawing included in the AD may be unclear; engineers must identify the exact members to be inspected. The background mentions “upper left and right hand members” but the requirement says “engine mount members” broadly - it may cover all tubular members. The safe interpretation is that all members must be inspected, but that may add significant labour.

Compliance is a multi‑step process that should be documented carefully. Step 1: Confirm applicability. The aircraft must be a Swift Museum Foundation GC-1B model, and the engine mount must bear part number 11-710-2520. Check the aircraft’s maintenance records and the part number stamped on the mount itself. If the aircraft does not meet both criteria, the AD does not apply, but keep a record of that determination. Step 2: Schedule initial compliance. The AD must be accomplished within six months after 17 September 2020, i.e., by 17 March 2021 for the first inspection. If the aircraft has already had an inspection meeting the requirements of this AD (for example, under FAA AD 64-05-06) before the commencement date, it counts as “previously accomplished” and no immediate action is needed, but the recurrent interval will run from that prior accomplishment. Step 3: Perform the inspection. This should be done by a licensed aircraft maintenance engineer. The engineer must:

• (a) Probe each engine mount member with an ice pick or equivalent tool to detect rust or pin holing.
• (b) If the member appears solid, remove any upper drive screw present, or drill a No. 37 size hole at the upper end of the member.
• (c) Drill another No. 37 hole at the lower end of the member.
• (d) Inspect the interior through the drilled holes for rust, water, or deterioration. Use an air nozzle if desired to expel moisture.
• (e) If the member is found to be damaged from internal corrosion, replace it. Cut out the old member and weld in a new member meeting the specification: 7/8 inch outer diameter, 0.035 inch wall thickness, 4130 steel heat treated to 85,000 p.s.i. yield. The weld must be done by a qualified welder and inspected.
• (f) For each member (whether original and sound or new), fill with Lionoil or equivalent slushing compound, then drain. This leaves a protective film inside the tube.
• (g) Plug the No. 37 holes with drive screws AN 535‑4‑3. Step 4: Record compliance. In the aircraft logbook, enter the AD number (AD/GC‑1/6), the date, aircraft total hours and cycles, the condition found for each member (including any replacements), the slushing compound used, and the engineer’s name, licence number, and signature. If any member was replaced, note the part number and weld inspection. If the AD was previously accomplished, note that and the date of that accomplishment. Step 5: Set recurrence. The AD must be repeated at each 100 hours time in service or every 12 months, whichever occurs first. Create a maintenance reminder system to ensure the next inspection is not missed. On each recurrence, perform the same procedure - probe, drill, inspect, treat, plug. Note that after the initial slushing treatment, the inside of the tubes should already be protected, but the AD still requires the full process each time. If the aircraft has flown less than 100 hours since the last inspection, the 12‑month clock still runs. Step 6: Maintain records indefinitely. Keep all AD compliance records as part of the aircraft’s permanent maintenance history. When selling the aircraft, provide the records to the new owner. Compliance with this AD also ensures continuing compliance with Part 42 of CASR and supports the issue of an airworthiness release. If any deviation from the AD’s procedure is needed (for example, if a drive screw cannot be sourced, or an alternative slushing compound is desired), seek prior approval from CASA. Do not assume an obvious equivalence without approval, as CASA may later dispute the validity of the compliance. For a fleet owner, consider standardising the process across multiple aircraft and training engineers on the subjective judgment criteria.