AD/PA-23/12 Amdt 2 - Empennage - Inspection

The central concept is empennage which refers to the tail assembly of the aeroplane including the horizontal and vertical stabilisers, elevators, and rudder. The AD targets specific structural components within that assembly. A critical distinction is between castings and forgings. Castings are produced by pouring molten metal into a mould, while forgings are formed by compressive forces, typically resulting in a denser, stronger part with better fatigue resistance. The AD explains that all the listed forged parts have integral raised digit forging numbers, so the absence of raised digits on a component indicates it is a casting and therefore subject to the inspection regime. This identification method is important because operators and maintenance engineers may be uncertain about which parts are installed on a particular aircraft.

Another key concept is time in service. This is measured in hours of operation and determines when the more demanding penetrant inspection becomes mandatory. The AD draws a threshold at 1000 hours time in service, after which the first penetrant inspection is triggered at the next scheduled maintenance release. Thereafter, the interval is 500 hours. These intervals are measured from the most recent penetrant inspection, not from the aircraft total time. The concept of maintenance release is the scheduled inspection event under the aircraft’s approved maintenance program, not an ad hoc check. The AD ties its requirements to that existing maintenance cycle, which minimises disruption but also means that if the aircraft flies many hours between scheduled inspections, the inspection interval may effectively be longer than the calendar time CASA would otherwise prefer.

The penetrant inspection method (fluorescent or dye) is a non-destructive testing technique used to detect surface-breaking cracks. The AD stipulates that the method must be an approved one, which generally means it must comply with the manufacturer’s recommendations or an equivalent standard acceptable to CASA. Use of zinc chromate primer after inspection is a corrosion prevention measure, reflecting the understanding that the process of cleaning and handling castings can expose bare metal. Finally, the concept of repetitive versus one-off compliance is central: a casting that remains in service must be inspected at each interval indefinitely, whereas a casting replaced by a forging ceases to require any further inspections under this AD. That creates a strong economic incentive to upgrade to forgings at the first opportunity.

This AD directly affects owners and operators of any Piper PA-23 or PA-23-160 aeroplane bearing serial numbers 23-1 through 23-1267. Given that these are older aircraft (the PA-23 first flew in the 1950s and production ended in the early 1980s), the population consists largely of privately owned light twins, small charter operators, flying schools, and possibly a few government or corporate operators. The AD imposes obligations on whoever is responsible for maintaining the aircraft’s airworthiness, which in practice is usually the registered operator or owner.

Licensed Aircraft Maintenance Engineers (LAMEs) and maintenance organisations are the parties who physically execute the inspections. The AD requires competence in visual inspection techniques and in performing fluorescent or dye penetrant inspections, including proper cleaning, application, and interpretation of results. The need to remove and reinstall castings with careful attention to Piper SB No. 155B means that engineers must have access to that service bulletin and follow its procedures precisely. This may require training or familiarisation for engineers who have not worked on PA-23 empennage castings before.

CASA itself is affected in its role as the regulator, because it must monitor compliance through its audit and surveillance programs. The AD is a tool CASA uses to manage an identified safety risk (cracking in empennage castings) without having to ground the entire fleet. By shifting from a 100-hour visual inspection to a 500-hour penetrant inspection with removal, CASA presumably achieves a better detection rate while reducing the frequency of the most labour-intensive task for older aircraft.

Suppliers of the forged replacement parts and of the required castings if replacements are needed are also affected, though indirectly. The AD creates demand for those parts, potentially increasing sales for Piper or aftermarket suppliers. However, the AD does not specify where to obtain the parts, only that they must be the correct Piper part numbers. If forgings are no longer in production, operators may face supply difficulties, which could extend the period during which they remain subject to repetitive inspections.

Insurers of these aircraft have an interest in compliance because a failure to adhere to an AD could void coverage or affect liability in the event of an incident. Similarly, prospective buyers of PA-23 aircraft now have additional due diligence: they must verify that the empennage castings have been either replaced with forgings or that the inspection history is complete and up to date. A history of non-compliance could significantly reduce the aircraft’s market value.

The primary duties imposed by this AD fall on the operator who must ensure that the inspections are carried out at the required intervals and that any cracked castings are replaced. The specific duties are:

• Remove the tail cone, covers, and fairings to gain access to the empennage castings.
• Visually inspect the six specified castings (elevator torque tube bracket part numbers 17033-00 and 17033-01, front stabiliser attachment part numbers 17049-00 and 19253-00, rudder torque tube horn part number 17060-00, elevator torque tube horn part number 17066-00, rudder torque tube bracket part number 17062-00, fin attachment bracket part number 17072-00) for cracks at each scheduled inspection for a maintenance release.
• For any casting that has accumulated more than 1000 hours time in service, remove it from the aircraft, clean it thoroughly to remove all paint, and inspect it using an approved fluorescent or dye penetrant method.
• Prior to reinstallation of any airworthy casting, clean it thoroughly and apply zinc chromate primer.
• If a casting is found cracked, replace it with a new casting or with the corresponding forged part listed in the AD.
• Perform the inspection and reassembly in accordance with Piper SB No. 155B.

The operator also has a duty to maintain records of time in service for each casting, because the penetrant inspection timing depends on each casting’s individual hours, not just the aircraft total time. This is a non-trivial record-keeping obligation, as it requires tracking which castings have been swapped between aircraft, when they were last inspected, and how much time has accumulated since.

The rights conferred are limited but meaningful. The most significant right is that once a casting is replaced by its respective forging, the repetitive inspections under paragraphs 1 and 2 of the AD cease to apply for that part. This gives the operator an exit strategy: by incurring the cost of a forging now, they can eliminate ongoing inspection costs and the risk of future inspection findings. Another right is that the operator may use either a casting or a forging as a replacement part, giving some flexibility in parts sourcing. The AD does not prohibit the operator from performing more frequent inspections if they wish, but it sets a floor, not a ceiling.

Maintenance engineers and organisations have the right to choose the specific approved penetrant method (fluorescent or dye) as long as it is acceptable to CASA. They also have the right to rely on Piper SB No. 155B as the definitive procedure for inspection and reassembly, meaning they do not need to devise their own methods from first principles.

Notably, the AD does not grant any explicit right to apply for an alternative means of compliance or an extension of the compliance period. The text gives no discretion. This is a command, not a guideline.

The AD itself does not specify penalties, but its legal force derives from the Civil Aviation Regulations and the Civil Aviation Act 1988. Under section 20A of the Civil Aviation Act, CASA may issue directions, and failure to comply with a direction that is a condition of an airworthiness certificate or a requirement of the regulations can constitute an offence. Specifically, operating an aircraft that does not comply with an applicable Airworthiness Directive is a breach of regulation 42ZC of the Civil Aviation Regulations 1988 (or the equivalent in the current Civil Aviation Safety Regulations). The maximum penalty for operating a non-compliant aircraft can be up to 50 penalty units (at current rates, approximately AUD 13,320 for an individual) or 250 penalty units for a body corporate, and/or imprisonment for up to two years in serious cases. Additionally, the aircraft’s airworthiness certificate or maintenance release may be invalidated, grounding the aircraft until compliance is achieved.

Enforcement is primarily the responsibility of CASA through its inspectors and the CASA Enforcement Manual. CASA may conduct audits of maintenance records, inspect aircraft on the ground, or even spot-check during routine operations. The AD’s requirements are specific and verifiable: an inspector can check the aircraft’s logbooks for records of the required inspections, look at the empennage castings to see whether they are cast or forged, and confirm that the correct primer has been used. Because the AD relies on time-in-service thresholds, CASA can cross-reference hours flown with inspection dates to identify non-compliance.

For maintenance organisations, the consequences of a finding of non-compliance can extend beyond fines to include suspension or revocation of their approval to perform maintenance on that type of aircraft. Licensed engineers may face disciplinary action from CASA, including suspension or cancellation of their license if they certify work that does not meet the AD requirements.

There is no mention of any civil liability in the AD itself, but a plaintiff in a tort claim could use non-compliance with an AD as evidence of negligence per se if a failure of an empennage part led to an accident. This exposure creates a strong private incentive to comply, independent of regulator enforcement.

The AD places the onus on the operator to determine which castings are fitted, to track their hours, and to ensure the inspection schedule is met. The operator cannot delegate legal responsibility for compliance to the maintenance engineer, even though the physical work is contracted out.

This AD operates within a hierarchy of aviation safety regulation. It is issued under Part 39 of the Civil Aviation Safety Regulations (CASR) or its predecessor under the Civil Aviation Regulations, which empowers CASA to issue Airworthiness Directives to correct unsafe conditions. The AD is therefore subordinate to the Act and Regulations but prevails over any inconsistent manufacturer’s service information.

The AD explicitly references Piper Service Bulletin No. 155B, incorporating it by reference as the mandatory procedure for inspection and reassembly. This means that the SB becomes legally binding to the extent set out in the AD, even though SBs are ordinarily advisory. Any deviation from the SB’s instructions (e.g., using a different inspection method or lubricant) would be a breach of the AD unless separately approved by CASA. The AD also references FAA AD 63-26-03, which is a United States Federal Aviation Administration directive on the same subject. For aircraft imported from the US or operating under bilateral agreements, compliance with the FAA AD may also be required for continued airworthiness certification. This AD clarifies that the CASA version is the controlling Australian legal instrument, but operators should be aware that the FAA AD may still affect aircraft on the US registry or those subject to FAA oversight.

The AD also interacts with AD/PA-23/91 “Elevator Butt Rib and Plate - Inspection”, to which inspections previously listed in Piper SB No. 146B have been transferred. This means that the removal of SB No. 146B from this AD does not eliminate the need for those inspections; they are now enforced under a separate directive. Operators must therefore check both ADs to ensure comprehensive compliance for empennage inspections.

General work health and safety laws may apply to the removal and handling of castings, especially during cleaning and use of chemical penetrants. Zinc chromate primer contains hexavalent chromium, a known carcinogen, so its use must comply with state and territory hazardous substance regulations. The AD does not address these occupational safety issues, but they impose separate duties on the maintenance organisation.

Contract law may come into play when an aircraft is sold; the contract typically requires the seller to warrant that the aircraft is in an airworthy condition and compliant with all applicable ADs. A buyer discovering a past failure to comply with this AD could sue for breach of contract or rescind the sale.

Finally, the AD interacts with the CASA regulatory framework for maintenance releases because it requires the inspections to be performed “at each scheduled inspection for issue of a maintenance release.” This ties the AD to the operator’s approved maintenance schedule, which itself must be acceptable to CASA. If the schedule changes, the AD compliance intervals may shift accordingly, as long as the intervals do not exceed the AD maxima.

The AD has undergone several iterations that reflect refinements in understanding of the cracking problem and adjustments to the compliance burden.

Original issue: The very first version specified a 100-hourly visual inspection of the empennage, referencing Piper Service Bulletins No. 146B and 155B, and was based on FAA AD 57-13-9. This was a relatively light but frequent inspection.

DCA/23/12A introduced a significant change: it added the requirement for a fluorescent or dye penetrant inspection, but set the interval at 500 hours. It also split the AD into a separate Compliance statement and a Requirement statement (placed in a supplement) to improve clarity. Importantly, this amendment deleted the reference to Piper SB No. 146B, indicating that those inspections were no longer considered necessary for the cracking issue or were being moved elsewhere.

AD/PA-23/12 Amdt 1 changed the title (presumably to match the new numbering convention) and amalgamated the Requirement statement and Compliance statement back into a single document, perhaps to simplify reading for maintenance personnel. No substantive technical changes were made at this stage.

AD/PA-23/12 Amdt 2 (the current version) made multiple clarifications. It specified that the serial number applicability is Models PA-23 and PA-23-160 with serial numbers 23-1 to 23-1267 (the earlier version had not limited the serial range in the applicability field). It also clarified the Compliance statement, ensuring that the requirement for visual inspection at each maintenance release was not confused with the penetrant inspection timing. It explicitly identified FAA AD 63-26-03 as the corresponding US directive, which aids operators with cross-border compliance. Finally, it removed the inspections specified in SB No. 146B from the AD and transferred them to AD/PA-23/91 “Elevator Butt Rib and Plate - Inspection”, a housekeeping measure.

From an economic standpoint, the history shows a progression from frequent, low-intensity inspections to less frequent but more thorough inspections (penetrant removal). This likely reflects a trade-off between detection capability and downtime costs. The move to every 500 hours for penetrant inspection instead of every 100 hours for visual inspection probably reduced overall labour hours for older aircraft, while the removal of simple visual inspection for some parts (transferred to another AD) may have increased the upfront work required at each 500-hour milestone.

The effective date of the current amendment is 28 August 2008. No subsequent amendments are noted in the source. Operators should verify whether later amendments have superseded this one, but the text provided does not indicate any changes after 2008.

The source text does not mention any litigation directly concerning AD/PA-23/12 or its amendments. This is typical for airworthiness directives, which are rarely the subject of judicial review or private litigation. Most ADs are complied with by the industry because the consequences of non-compliance are immediate (grounding and loss of operating certificate) and the technical basis is usually well supported by accident or incident investigations.

However, there may be indirect litigation. For example, if a component failure occurred that the AD was designed to prevent, a plaintiff (or the Australian Transport Safety Bureau) would examine compliance records. If an operator had failed to perform the required inspections, that would likely be a central fact in any negligence lawsuit or in a coronial inquest. The AD would be used as evidence of the standard of care expected of a reasonable operator.

From a regulatory perspective, CASA may have taken enforcement action against specific operators for non-compliance, but such actions are typically not published in a form that generates “litigation” in the traditional sense. They are often resolved by enforceable voluntary undertakings, civil penalties, or administrative decisions that may be appealed to the Administrative Appeals Tribunal (AAT). No such decisions are referenced in the source, and it would be improper to speculate about unreported cases.

The absence of published litigation does not mean the AD is uncontroversial. It simply means that disputes, if any, have been resolved without generating a published court or tribunal decision. Given the age of the aircraft and the relatively narrow scope of the AD, the potential for litigation is confined to property damage or personal injury arising from a catastrophic failure of an empennage casting. Since no such event is recorded in the source, the litigation history is effectively nil.

Several aspects of this AD create traps for the unwary operator or maintenance engineer.

Distinguishing castings from forgings. The AD notes that all forged parts have integral raised digit forging numbers. Absence of raised digits identifies the part as a casting. However, parts may be painted or coated in a way that obscures the raised digits, or an engineer may mistake a clear cast part for a forging because the surface is smooth. The AD does not require a metallurgical test, only visual inspection for raised digits. But if a part lacks raised digits because they were ground off during a previous repair, the engineer might incorrectly assess it as a forging and omit the required inspection. Conversely, if a forging is incorrectly identified as a casting, the operator might perform unnecessary inspections. The safest approach is to consult the aircraft’s parts manual or logbook records.

Time in service tracking for individual castings. The AD requires the penetrant inspection for castings with more than 1000 hours time in service. Does that refer to total time on the aircraft, or time since the casting was new? The text says “time in service” without qualification. If a casting is replaced, the new casting starts at zero hours. But if an aircraft has multiple castings, each may have a different time in service if they have been replaced or swapped between aircraft. The AD does not require marking hours on the casting itself; it relies on logbook entries. If an operator loses track, they may inadvertently let a casting exceed 500 hours since its last penetrant inspection. The only safe practice is to treat the first penetrant inspection as mandatory at the aircraft’s first scheduled maintenance release after 1000 hours total airframe time, and thereafter maintain a separate record for each casting’s inspection date.

The 500-hour interval is measured from the last penetrant inspection, not from the aircraft’s total time. An operator might assume that once a casting has passed its initial penetrant inspection, the next one is due at 1500 hours aircraft time. But if the aircraft flew only 400 hours in two years, the next inspection would still be due at 500 hours since the last inspection regardless of calendar time. The AD provides no alternate calendar-based limit, so an aircraft that flies infrequently could theoretically go years between inspections if it stays under 500 hours. That may be acceptable under the AD but could conflict with other maintenance requirements or manufacturer recommendations. This is not a flaw in the AD but a potential gap an operator might exploit, though doing so would increase risk.

Visual inspection frequency. Paragraph 1 requires visual inspection at each scheduled inspection for issue of a maintenance release. The typical PA-23 maintenance release interval is 100 hours or annually, whichever comes first. So visual inspection is more frequent than penetrant inspection. An operator might think that if they comply with the penetrant inspection at 500 hours, they can skip the visual inspections in between. That would be a breach. The AD requires both, cumulatively.

No alternative means of compliance. Unlike some CASA ADs that allow alternative methods if approved by the Director, this AD states no such provision. The only “exit” is replacing the casting with a forging. An operator who develops a superior inspection technique cannot use it unless it is exactly the approved penetrant method. This removes flexibility.

Zinc chromate primer requirement. The AD specifies “zinc chromate primer.” Modern corrosion-inhibiting compounds may use strontium chromate or other substances. Using the wrong primer, even if superior, would technically breach the AD unless the primer meets the specification. Operators should check the primer against the Part Number or specification in Piper SB No. 155B.

Reference to Piper SB No. 155B. The AD does not reproduce the contents of that SB. Operators must obtain the current version of the SB. If the SB has been revised or withdrawn, compliance could become uncertain. The AD does not specify a revision level, so presumably the version in effect at the time of the AD (2008) is required, but later revisions may be acceptable if they are equivalent or superseding.

Compliance involves a layered approach that begins with identification of the aircraft’s applicability and ends with documentation. The steps are as follows.

Step 1: Confirm applicability. Check the aircraft model (must be PA-23 or PA-23-160) and serial number (must be between 23-1 and 23-1267). If the serial number is outside this range, the AD does not apply. If the aircraft has been modified to a different empennage configuration, the AD may still apply unless specifically excluded in a supplemental type certificate. Contact the manufacturer or CASA for guidance if in doubt.

Step 2: Determine configuration. For each of the six listed parts, inspect the part to determine whether it is a casting or a forging. Look for the presence of raised digit numbers on the part. If raised digits are present and match the forging part numbers (19407-00, 19409-02, 19405-00, 19404-00, 19408-00, 19406-00 or 19406-02), the part is a forging and no further action is required. If there are no raised digits, the part is a casting and must be placed on the inspection schedule.

Step 3: Establish initial inspection timing. If any casting has less than 1000 hours time in service at the date of the first compliance after the AD effective date, only the visual inspection (paragraph 1) is required at the next scheduled maintenance release. The penetrant inspection (paragraph 2) will become due at the first scheduled maintenance release after the casting reaches 1000 hours. If the casting already has more than 1000 hours, the penetrant inspection is due at the next scheduled maintenance release (if not already done) and then every 500 hours thereafter.

Step 4: Perform visual inspections. At each scheduled inspection for a maintenance release, remove the tail cone, covers, and fairings to gain access. Visually inspect the six castings for cracks. No penetrant is required. If a crack is found, replace the casting immediately. If no crack is found, reassemble per Piper SB No. 155B. Record the inspection in the maintenance release and logbook.

Step 5: Perform penetrant inspections. When the casting reaches the threshold (over 1000 hours for the first time, or after 500 hours since the last penetrant inspection), remove the casting from the aircraft. Clean it thoroughly to remove all paint. Apply an approved fluorescent or dye penetrant method as described in Piper SB No. 155B (the AD does not specify the exact method; the engineer must use a method approved by CASA, typically referencing a standard such as ASTM E1417). Inspect for cracks. If a crack is found, replace the casting with a new casting or the corresponding forging. If no crack, clean the casting again and apply zinc chromate primer. Reinstall the casting and reassemble the empennage per the SB. Record the date and hours in the aircraft maintenance log.

Step 6: Replace castings with forgings to terminate inspections. The AD gives a strong economic incentive to do this. When a casting is replaced by its corresponding forging (using the forging part numbers listed in the table), no further inspections are required for that part. The operator should verify that the forging part numbers are correct and that the part has the raised digits. Replace one component at a time to minimise downtime. After replacement, update the aircraft records to show the part is now a forging and that compliance with the AD for that part is complete.

Step 7: Maintain records. Keep a log of each casting: its part number, identification (casting or forging), time in service, date of each visual inspection, and date and hours of each penetrant inspection. This record must survive aircraft transfers. Use a spreadsheet or dedicated airworthiness tracking system.

Step 8: Review and update. If the aircraft receives a new casting from a different source, ensure it is tracked correctly. If Piper issues a revision to SB No. 155B, check whether the AD still references it; if not, the original SB may still be the binding document. If CASA issues a new amendment to this AD, repeat all steps accordingly.

Step 9: Engage a qualified engineer. All inspections must be performed or supervised by a person holding the appropriate LAME category for the airframe. The engineer must sign off the work in the maintenance release. Ensure the engineer is familiar with the AD and has access to Piper SB No. 155B.

The total cost of initial compliance will depend on the number of castings that require penetrant inspection and whether any are cracked. For an aircraft with six castings all over 1000 hours, the first penetrant inspection will involve significant labour (removal, cleaning, inspection, reassembly) plus consumables (penetrant kit, primer). However, once the castings are replaced with forgings, the ongoing inspection burden drops to zero. Therefore, the most cost-effective strategy may be to allocate the cost of forgings early, rather than paying for repeated inspections over the remaining life of the aircraft. The AD does not mandate that strategy, but the economics of compliance favour it.