How Does Airworthiness Directive Impact Redelivery, Planning & Safety?

Earlier this year, the Alaska Airlines incident made headlines when an NTSB investigation revealed missing bolts caused a mid-air door blowout. Consequently, the FAA issued Emergency Airworthiness Directives (ADs), grounding 171 Boeing 737-9 aircraft for inspection. While the Alaska Airlines case is certainly extreme, this incident underscores the necessity of ADs, which are regularly issued to ensure the ongoing airworthiness and safety of all operating aircraft.?

Airworthiness Directives (ADs) are mandatory rules enforced by aviation authorities to address unsafe conditions. These directives can be triggered by engineering analysis results, repetitive incident reports, or accident investigation findings, and may require inspections, parts replacements, maintenance tasks, or even grounding in urgent cases. Compliance with ADs is critical for maintaining a Certificate of Airworthiness (CoA); failure to comply can lead to its loss and the costly consequence of grounding the aircraft.

AD Compliance Needs Extensive Maintenance Planning

Noting its impact on airworthiness, AD compliance is critical for operators, whether during redelivery preparation or ongoing operations. However, maintaining compliance can be complex. Let’s use a quite recent AD as an example:

Case Study: Potential Oxygen Mask Issue on 737s, AD Estimated to Impact 2600+ Aircrafts

In early July 2024, the FAA published an AD for several Boeing 737-Max and 737 NG models due to reports of PSU oxygen generators shifting out of position, caused by the failure of pressure-sensitive adhesive (PSA) material on certain generator strap thermal pads, an issue that could prevent supplemental oxygen from being provided to passengers during a depressurization event. To prevent similar issues, operators are required to conduct a general visual inspection to identify if any PSU oxygen generators are using PSA retention strap thermal pads. If any are found, operators have to conduct a GVI on said PSU oxygen generators if expended and installation migration and, depending on the findings, replace the affected PSU oxygen generator, replace the PSA strap thermal pads with non-PSA thermal pads, or reposition affected PSU Oxygen Generator (exact action, condition, and compliance time is based on the model).

Using this AD as an example, compliance at the very least requires time and personnel for inspections, hangar space, on top of on-condition replacement parts –in this case, replacement PSU oxygen generators or strap thermal pads– and related tools to ensure the safety of the about 60 PSU oxygen generators and the 2 pads each have in an aircraft.?

As the number of ADs rises, so do the tasks, preparation, and costs that operators must consider. Thorough planning is essential to account for everything from personnel schedules, fleet availability, material availability and procurement timelines, hangar spots, to AMOC proposal drafting (if necessary) to ensure timely execution and manage maintenance costs. Operators oftentimes have meetings and procedures in place to not only plan tasks for AD compliance, but also identify complexities (such as the risk of AD changes, workload intensity, and repetitive inspections), verify compliance (including record verification), and even create staggering plans to maximize on-wing time.

Does Airworthiness Directives Impact Redelivery Timeline & Cost?

Absolutely, AD can and will cause redelivery delays if there are:

• Overdue ADs: These need to be addressed to maintain airworthiness, which can impact both asset value and lease agreements.
• Missing DFP Last Compliance for Repetitive AD: This involves ensuring compliance with repetitive ADs for inspections and parts replacements, including the necessary documentation for each action.
• Unmet Clearance Period Compliance: ADs must be fulfilled within a certain period after redelivery, known as the 'clearance period.' The length of the clearance period is typically settled during lease negotiations.
• AMOC between jurisdictions: Operators can file for an Alternative Method of Compliance (AMOC) to address issues differently or on a different timeline than prescribed. AMOCs must be approved by the relevant authority and are not automatically transferable between jurisdictions. During redelivery, it is crucial to consider this, as procedures may need to adapt the executed AMOC, the new operator needs to follow the original method/time or propose a new AMOC (IATA, 2017).

So, Which Airworthiness Directives Should My Aircraft Follow?

Legally ADs are governed by the respective local aviation authorities, but many automatically deem foreign ADs issued by the aircraft's State of Design, such as those from EASA and FAA, to be applicable domestically, with some exceptions or additional requirements. For example, Indonesia’s CASR Part 39 notes possible reconsiderations in compliance time to account for domestic contexts. EASA, FAA, and other aircraft manufacturing countries maintain directories listing all issued ADs and note if past ADs have been superseded (EASA Safety Publications Tool, FAA Dynamic Regulatory System).

All These Extra Maintenance Actions, Who is Paying for It?

ADs are regularly updated, with both EASA and FAA hundreds of them annually. Consequently, this creates additional tasks for operators. The frequent updates and resulting workload to no surprise open the debate over who should bear the cost of compliance, especially as ADs become more common.

Generally, owners/operators usually manage the financial costs related to AD compliance. However, costs can sometimes be managed through a cost-sharing scheme with lessors, as specified in lease agreements, though it is still a point of contention (IBA has an informative article section -we’d recommend giving it a read). In some cases, OEMs may cover some costs through warranty claims, as noted in certain AD notices (see this AD by the FAA as an example). This unsurprisingly remains a much-debated topic, with both parties arguing why the other should cover the costs.

Need support for redelivery or maintenance planning? TBM Aviation got your back

TBM Aviation’s Aircraft & Engine Transition Services and maintenance planning include everything from agreement review and meticulous records audits to thorough inspections and maintenance claim reviews, ensuring a smooth transition for your asset. Complementing these, TBM Aviation’s Engineering & Planning Services provide a customizable technical solution to maintain airworthiness for your fleet through tailored maintenance programs and skilled component management to help you manage costs and ensure regulatory compliance.

Resource & References

EASA Safety Publications Tool (AD/SD/SIB)

FAA’s Dynamic Regulatory System

IATA's Guidance Material and Best Practices for Aircraft Leases