If you have ever unwound and bent a paper clip to and fro until it snapped, you understand the concept behind metal fatigue.
Railroad engineers in the late 19th century were the first to recognize the problem. As NASA’s Brent Wellman wrote in 1997, “A large number of accidents involving train axles which SHOULD have easily handled the loads on them, led engineers to describe the parts as being ‘tired,’ or ‘fatigued.'”
Metal fatigue entered the Jet Age with the tragic tale of the de Havilland Comet. The first commercial jetliner disintegrated in flight in 1954, killing all the passengers and crew. After a massive and expensive effort, investigators determined cracks formed near the Comet’s windows causing the pressurized cabin to fail which lead to a catastrophic in-flight breakup.
The Comet experience prompted significant changes in the way airliners are designed. The aluminum skins were thickened, the windows made smaller and the metal near them reinforced. Problem solved – more or less. The only fatal airline incident linked to metal fatigue since the Comet crashes occurred on a 737 flown as Aloha Airlines Flight 243 on April 28, 1988. Fatigue and corrosion caused a lap joint to fail – and an 18-foot long piece of skin blew away, exposing the first-class section above the window level. Flight attendant Clarabelle Lansing – who was walking in the first class aisle – was ejected from the open aircraft at 24,000 feet.
Aloha Airlines 737s flew a lot of short runs; on average three “cycles” (a take off and landing) per hour of flight. That is twice what Boeing considered when it prescribed a maintenance and inspection regime for the 737. As it turns out, cut-rate Aloha’s maintenance practices were pretty slipshod anyway.
Inspecting for metal fatigue does take time and effort. Engineers say it begins with tiny cracks at the molecular level. The cracks spread and grow gradually as forces that are not strong enough to cause the metal to completely fail are applied and released over time. Eventually, the cracks become large enough to see, but they are a hazard long before then.
The manufacturer and the FAA mandate inspections of critical spots on an aircraft with non-destructive testing equipment to find these invisible cracks. Typically, they send some electric current through a section of metal. A sensor measures the variations in the alternating current that flows though the metal. Cracks that cannot be seen by the naked eye will disrupt the flow of the juice enough to reveal lurking trouble.
But the lap joint that recently failed on the Southwest 737 was not in an area that would have been subjected to these so-called “eddy current” tests. The airplane that failed has nearly 40,000 cycles of pressurization and depressurization – that is a lot of bending of the paper clip. Maybe it is time to rethink the inspection requirements for these airplanes. Clearly, what is being done now is not enough.
Southwest outsources 70-75 percent of its maintenance. The so-called “heavy” checks where they periodically pick the plane apart like a Thanksgiving turkey occur overseas in places like Guatemala and China. This practice is now the industry norm. The legacy airlines (with the exception of American) have moved the majority of their maintenance work out of their hangars and into the hands of airline maintenance job shops.
Earlier this year, I reported for PBS FRONTLINE on this subject in a segment called “Flying Cheaper.” It was a follow-up to “Flying Cheap” – which delved into the crash of Continental Flight 3407 in Buffalo and safety concerns associated with regional airlines. Now, just because the work is done outside the airline — and often outside the country — does not inherently mean it is less safe. But there are some reasons to be worried.
For one thing, the international language of aviation is English. The manuals for the airplanes are written in English, and the FAA requires that anyone who works on the planes be able to read the instructions well enough to comprehend them. In the real world, this is often not the case.
The other big worry is the level of transparency once the work moves offshore. The FAA simply does not have the resources — or the visas — to “pop-in” for a visit at a maintenance hangar in China. The inspection requires months of notification and planning – and when inspectors arrive the hangar is not-so-surprisingly shipshape and the workers are lined up in uniforms.
So what is really going on in these hangars on a day-to-day basis? Wish I knew. FRONTLINE asked several of these maintenance companies for access inside the hangar doors. They would not let us in. What are they hiding?
Ironically, the push toward cheaper, outsourced maintenance is a response to the competitive threat posed by upstart Southwest – which has managed to consistently turn a profit in the rough and tumble post-deregulation world of airline operations. One of the stories that we explored in “Flying Cheap,” but had to leave on the cutting room floor for lack of time, focused on Southwest Airlines and its relationship to the FAA inspectors inside its hangars.
Interestingly, it all began with concerns over corrosion and metal fatigue on the crown of the airplane. The FAA issued a series of Airworthiness Directives (or ADs) after the Aloha incident mandating certain inspections to that portion of the 737.
An AD is not an item to be ignored. It must be completed as stated in the time frame allotted — or the aircraft in question is no longer considered legal to fly in revenue service.
FAA inspector Bobby Boutris was in charge of watching over the Southwest 737-700 fleet in Dallas. Through some sleuthing, he discovered that the airline had not completed the inspections laid out in the AD on 47 airplanes that were still flying paying passengers.
He reported this problem to his supervisor at the FAA. His boss ignored him and promptly had him reassigned. Boutris then called an investigator with the House Transportation Committee, and spilled the beans. Another inspector, Doug Peters, backed him up and agreed that the supervisor, Douglas Gawadzinski, was covering up for the airline and allowing airplanes that were not legally airworthy to fly.
The whistle-blowing worked. The call triggered a blockbuster of a congressional hearing, forced the FAA to fine Southwest Airlines $10 million and led to an egg-on-face, knee-jerk crackdown on maintenance at other airlines — including American.
Turns out Gawadzinski was very chummy with Paul Comeau — a former FAA inspector who had passed through the revolving door into the employ of Southwest Airlines.
The culture of coziness came from on high. The FAA had been pushing a “good cop” approach to airline regulation known as the “Customer Service Initiative.” The idea: encourage the airlines to self-report problems and the net result will be enhanced safety.
But wait a minute: aren’t we the customers? In telling the FAA troops to treat the airlines as such, the agency brass confused its inspectors about what their mission truly is.
The aviation world is a small one, and within it there is a natural tendency for inspectors who are “embedded” to develop misplaced allegiances.
Aviation professionals will remind you that airline travel is the safest mode of transportation ever devised. The redundancies in the system – from aircraft design to crew training – made it possible for the crew of Southwest flight 812 to bring that damaged 737 in for a landing.
But many experts have been warning that the industry is eating away at a safety margin built over time and tragic experience in order to trim costs. This latest incident proves yet again there are some serious cracks in the system.