Aircraft Maintenence Technology: FAA Wants to Limit Fatigue Damage On Aging Commercial Planes

Air Safety Week
via NewsEdge Corporation

May 2, 2006

While the Federal Aviation Administration's (FAA) April 18 proposal to mitigate widespread fatigue damage (WFD) in aging transport aircraft through operational limits is intended to make the aviation industry more proactive with WFD problems, some aviation safety experts aren't so sure that will happen. But they give different reasons for their uncertainty.

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. [DAHs] would also be required to determine if maintenance actions are needed to prevent [WFD] before an airplane reaches its operational limit."

Also, the agency says that "operators of any affected airplane would be required to incorporate the operational limit and any necessary service information into their maintenance programs. Operation of an affected airplane beyond the operational limit would be prohibited, unless an operator has incorporated an extended operational limit and any necessary service information into its maintenance program." The proposal would affect aircraft with maximum takeoff gross weights of 75,000 pounds or more.

Despite their initial reservations, former National Transportation Safety Board (NTSB) Chairman Jim Hall and Professor Chuck Eastlake of Embry-Riddle Aeronautical University say that the NPRM is a welcome development.

On the one hand, Hall, now a private consultant in Washington, D.C. with Hall and Associates, says that placing the onus of responsibility on the manufacturers and airlines is not the right focus. The Bush administration, he tells Air Safety Week, is particularly averse to regulations and enforcement. We have a safe aviation system, he says, because it's generally recognized that the government has a fairly substantial role to play. But the current administration wants to get results by using too few people and too few resources.

Hall was former President Clinton's NTSB Chairman, initially getting confirmed as a board member in October 1993, about 10 months after the start of Clinton's first term. In May 1994, Hall was appointed as the board's vice chairman, then moved up to chairman roughly two months later. He resigned from the NTSB on Jan. 19, 2001, a few days before the beginning of the Bush presidency.

Moreover, Hall adds that the NPRM "swims against the tide of common sense" by expecting that aircraft designers or operators, with the company bottom line and economic self-interest getting in the way, will do the best job. "None of us does a very good job of policing ourselves."

Then too, all the data for monitoring aircraft safety is supposed to originate with manufacturers, Hall adds. This presents a certain "chilling factor" from the point of view of manufacturers, who may be reluctant to release some information or respond as FAA wants, because of litigation concerns.

In a related development, the Flight Safety Foundation commended the council of the International Civil Aviation Organization (ICAO) at its annual European safety seminar in March, for approving provisions intended to prevent safety information from being used in legal proceedings against operational personnel. Before taking effect, however, the provisions would have to be adopted as national laws and regulations by ICAO member states.

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.

Also, as an instructor, he's taught students for years how to calculate the fatigue-related operational life of various aircraft. Even though he's never worked as a specialist in structural fatigues or fractures, Eastlake says that it's always been his impression that operational-life predictions need to be done mathematically. Furthermore, critical pieces of these calculations have to be based on actual aircraft testing. When an aircraft reaches that mathematically calculated point, then it needs to be taken out of service.

It's also part of Eastlake's understanding that extensions of aircrafts' operational lives have been a possibility for years, although they are rare. The main reason for this is that the inspection schedules become too expensive.

As some media outlets reported, FAA estimates that its proposal would cost the industry $360 million. But left out of those accounts is the fact that these costs would be spread over 20 years. The agency also states that "the present value benefits" of the proposal will total $809 million due to accident prevention and a reduction in unscheduled maintenance and repairs, also accrued over the same 20-year time period. Moreover, out of the $360 million in total costs, only 10 percent of that would be incurred by airplane manufacturers. The remainder would be borne by operators.

Normally, one would assume that the $360-million figure should be subtracted from the $809-million figure to arrive at a total $449 million economic benefit over the next two decades. FAA did not respond to Air Safety Week's requests for clarification.

Another part of the NPRM that deserves a public airing, Eastlake says, would enhance current regulations, which only require that manufacturers analyze the fatigue-based operational life of a part that has a single flaw or a single crack. FAA now has proposed a similar but more detailed analysis, with the assumption that one part can have more than one crack.

The full NPRM is in the April 18 Federal Register (FR Doc. 06-3621; Docket No. FAA-2006-24281) starting on p. 19928. It also can be downloaded at http://www.access.gpo.gov/su_docs/fedreg/frcont06.html.

Contacts: Jim Hall, Hall and Associates, (202) 312-0600; Chuck Eastlake, Embry-Riddle, (386) 226-6000; Walter Sippel, FAA, (425) 227-2774.