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Best Practices For AMOCs To Airworthiness Directives

Airlines, MROs can save time and money by identifying alternate methods of compliance (AMOC) for FAA airworthiness directives

When an airworthiness directive (AD) is released, it specifies the steps that must be followed in order to comply with it. In some cases, however, an airline engineering staff or MRO provider might opt to comply using an alternative method of compliance (AMOC).

“An AMOC gives the airline a choice,” states Andrew Richardson, sales director of Shannon-headquartered Eirtech Aviation. “It may be economically more interesting to offer an AMOC to save downtime, costs, and complexity—providing there are sufficient numbers of aircraft flying, or the development costs versus return make sense.”

Both the U.S. FAA and Europe’s EASA may allow the operator to pursue an AMOC, as long as it results in the same level of safety required to satisfy the AD’s requirements.

“The evolution of ADs is from ‘remove this part from your aircraft’ to telling the owner/operator exactly how to remove the part,” says Sarah Mac-Leod, executive director of the Aeronautical Repair Station Association (ARSA) in Washington.

In most cases, the FAA and EASA task the design approval-holder—usually the type or supplemental type certificate (STC)-holder—to develop a fix, once an unsafe condition has been determined. The aircraft manufacturer will then tap its supplier(s) to develop that fix, which is usually issued as an OEM service bulletin (SB). However, the AD compliance method could simply reference the aircraft maintenance manual for a relatively simple process, such as disconnecting a lavatory light.

MacLeod points out that the FAA is supposed to determine the cost of following the compliance procedure the AD has established. “If the operator determines that another method is more cost-effective, and wishes to perform differently anything contained in the referenced document, it must obtain an AMOC approval from the FAA,” she notes.

John Hazlet, vice president of the Hyannis, Massachusetts-based Regional Air Cargo Carriers Association (Racca), explains that an AD AMOC solution is (normally) pursued because it “is more economical, less time-consuming or better-suited to the manpower, facilities, parts and materials available to get the work done.” He adds that an AMOC could also be more appropriate for the airline’s fleet mix. “If the AD is targeting some article used on Boeings, Airbuses, and Douglas airplanes, and the AD was written by someone who was mostly Boeing-literate, there might be an easier way to access that article or accomplish the work on an Airbus or Douglas product that produces the same result.”

Issues like this, says Hazlet, are often addressed by operators or OEMs who submit comments when the AD goes out as a notice of proposed rulemaking (NPRM). “The FAA may then insert some changes into the final rule; but sometimes not, as in the case of an emergency AD that’s rushed into effect.”

Hazlet warns that if the carrier is considering an AMOC,” it has to be prepared to support its position with very strong and detailed technical data.

“You have to be able to demonstrate, conclusively, that your proposed AMOC will maintain the integrity of what the AD is intended to address or repair,” he says. “In some cases, in order to do this, the airline may have to engage the services of a designated engineering representative [DER], a designated airworthiness representative [DAR], or someone else with the appropriate engineering expertise. Typically, large airlines have the engineering capability in-house, but the smaller operators do not. And the outside experts don’t work for nothing.”

The AD AMOC process requires best practices, which means doing your homework. “A good place to start is Title 14 of the Code of Federal Regulations—specifically 14 CFR39.19 That’s what codifies the ability to pursue an AMOC.”

He also advises reading FAA Order Number 8110.103A. “This is AMOC 101, a textbook on what’s required to develop and submit an AMOC application.”

Hazlet recommends reading through the AD, paying particular attention to the end of the document, which specifies all the methods of compliance, the FAA’s willingness to allow an AMOC, and the name of an FAA representative to contact with questions.

Because of OEM involvement in producing the documentation referenced in the AD, there’s a question about to what degree the OEM will assist a company with an AMOC. That, says Hazlet, depends on the vendor. “They may provide a substantial amount of data, while others will not discuss it. And some will help, but will bill the customer for expenses, such as engineering time. If you can’t get OEM cooperation, it’s best to seek the advice of a DER or DAR.”

Kent Horton, director of aircraft engineering for Southwest Airlines, reports his company makes about “a couple dozen AMOC applications per year,” mostly due to variations in the aircraft configuration from that anticipated in the AD documentation.

“These variations in configuration—from that anticipated in the AD mandated documentation—create a situation where there is an inability to execute the AD precisely as written. Often, alternative procedures for gaining access are needed due to the configuration being different than expected.”

In fact, says Horton, most of Southwest’s AD AMOC applications pertain to inspection techniques for parts that cannot easily be removed for inspection on a workbench, given structural barriers. “In those cases, we may propose an AMOC that will allow a visual inspection of the part at more frequent intervals, rather than pulling it for non-destructive inspection.”

“When we begin the AMOC process, we will either petition the FAA directly, or we will do so through the airframe OEM, if the OEM has the AMOC authority from the FAA for the required solution. Most ADs are based on one or more OEM service bulletins, incorporating the compliance procedures, and the FAA will direct you to them.” He adds that in some cases, the OEM will have already approached the FAA with an AMOC in the form of a service bulletin revision.

Horton points out that a majority of Southwest’s heavy inspections are outsourced to independent MROs. “If there is an AD compliance issue discovered at the MRO level, they will notify us, and at that point, we handle it. We then go through a very structured process to develop an AMOC.”

The first step, he explains, is the “discovery effort” which means “understanding the true nature and details of the system configuration,” while in the second step, the compliance options are assessed.

“Then you need to assure that whatever options are selected, you will come out with the equivalent level of safety—and [that] you have the ability to accomplish that,” Horton notes. “All parties need to focus on the key safety aspects, as well as the details with regard to accomplishing the task. This requires excellent communication among the airline, the OEM, the FAA, and, when appropriate, the MRO.”

While costs are also considered, Horton stresses that they are “not weighted that heavily” when selecting AD compliance options. “Cost estimates are often included in the NPRM process leading up to the airworthiness directive issuance. Stakeholders will often provide comments and additional information regarding costs as part of the NPRM process.”

Eirtech Aviation’s Richardson advises that simplicity is among the best practices to control costs and downtime. “Look at a solution from the ground up, and try to keep it simple and avoid any complicated areas,” he says, citing an AMOC recently developed for Canadian carrier WestJet’s fleet of Boeing 737NGs, addressing an AD on the advanced warning cabin- pressurization system.

“Our AMOC totally avoided Junction [J] 46. This not only saves time and costs, but avoids other systems going through J46 and associated testing. J46 is a point on the 737NB where a number of systems converge. If you effectively disconnect anything going through this junction or modify [it], all associated systems would need re-checking afterward.”

Richard Mills, director of quality assurance for Hayden, Idaho-based Empire Airlines, says many of the company’s AMOCs have to do with paperwork driven by revisions to documents, such as the OEM service bulletins referenced in the ADs. “For example, let’s say an AD’s instructions specify accomplishing a modification in accordance with manufacturer’s service bulletin Revision 1,” he says. “The AD’s instructions might allow the operator 2,000 flight hours or one year from its effective date to accomplish the AD, so the operator schedules accomplishment six months later. In the meantime, the manufacturer issues revision 2 with substantive changes to the accomplishment instructions. Consequently, the operator who is reviewing service bulletin revisions will choose to apply for an AMOC that will allow him to use the later revision.”

As Mills explains, there have been times when the FAA has issued an NPRM for an AD with a long comment period, and by the time the final rule is published, the referenced service bulletin has been revised. However, the FAA has not modified the text in the published document to require accomplishment using that revised service bulletin. “This situation would require applying for an AMOC.”

Mills adds that if a service bulletin has been superseded—and the one referenced in the AD is no longer available—the operator has no option but to apply for an AMOC. He cites a case involving a member of the ATR family, of which Empire operates 31.

“AD2008-13-19 paragraph (f)(2) required replacement of the pitot probe current sensors on the ATR 72-212 in accordance with Avions de Transport Regional (ATR) Service Bulletin ATR 72-30-1042, Revision 1, dated June 1, 2005. The AD itself, incorporating Revision 1, did not become a final rule until 2008. By the time accomplishment was possible, ATR 72-30-1042, Revision 2, dated Jan. 15, 2009, had been issued. We requested an AMOC to use Revision 2. In this case, because Revision 1 was no longer available from the manufacturer,” says Mills.

The FAA was satisfied that use of the later revision provided an acceptable level of safety since it accomplished the intent of the AD and adequately addressed the unsafe condition identified by the AD. “The benefit to us in this case was obvious: The revision was our only available means to comply with the AD,” says Mills. 

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