FAA Wants to Limit Fatigue Damage On Aging Commercial Planes

In the Notice of Proposed Rulemaking (NPRM) with a public comment period set to end on July 17, FAA proposes to "require that design approval holders [DAHs, or airplane manufacturers] establish operational limits on transport category airplanes.


Still, Hall adds, FAA's proposal could work if it's "monitored correctly." Everyone concerned, not just FAA, will have to stay on top of how it pans out.

Meanwhile, Eastlake can't figure out what the NPRM would change. DAHs always have had the responsibility of determining the operational lives of specific aircraft and determining the proper maintenance schedules. "My primary impression is this NPRM is asking for things that have been done for decades," he tells Air Safety Week.

Eastlake has been involved with aircraft structural design for about 40 years, originally for General Electric and the U.S. Air Force, and has taught the subject for 28 years.

Especially since the 1988 Aloha Airlines accident and the Swissair accident in the mid 1990s, such an action is "unbelievably overdue," Hall says. The need for more attention in this area is obvious. Hopefully, the proposal at least serves to establish a "more comprehensive framework" than what exists now.

FAA cites the Aloha accident, in which an 18-ft. section of the upper fuselage of a Boeing 737 separated from the airplane on an inter-island hop, and for which the NTSB said WFD was a cause, as something of a watershed event for growing WFD concerns. Since that accident, WFD "appears to have played a role in several safety incidents involving large transport airplanes, although there has not been a catastrophic accident directly attributable to WFD."

For his part, Eastlake believes that manufacturers, operators and others may state during the public comment period that they already do much of what FAA is calling for in the NPRM. Thus, as the agency has done in many prior cases, the final rule may be very different from the NPRM. Or, if it finds nothing to fix, FAA also may decide it doesn't need any new rulemaking.

But FAA says that its "existing requirements, even those that incorporate the latest mandatory changes introduced to combat structural degradation due to WFD, creates a risk of structural failure and related accidents because the requirements are inadequate to preclude WFD."

Therefore, "we need a proactive approach [to] address conditions affecting safe flight that we know can happen--before they happen. This approach would require persons to analyze the causes of WFD in relation to the entire airplane and to analyze repairs, alterations, and modifications installed on the airplane."

Moreover, the agency feels that a more proactive approach has long been hampered by the fact that airlines are obliged to take new safety actions, while the manufacturers are not required to produce the necessary data and documentation to make the airlines' efforts more efficient and less costly.

To back up this point, FAA sites five examples involving such components as thrust reversers and reinforced flightdeck doors where carriers have had to develop new procedures and make repairs with little or no help from the designers, and thus having to reinvent the wheel by conducting their own research and data-collection procedures. (The full text of these examples are in the box on p. 2.)

FAA also notes that some DAHs have committed to providing the agency with data to aid in aircraft certification, but have missed the submittal deadlines by up to 13 years.

But on this same point, Eastlake says, "That's not my experience." Rather, he's had 30 years experience of witnessing manufacturers doing fatigue testing of wings, fuselages, and entire aircrafts.

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