The American aviation system is the safest in the world, in part because of the quality of the repair and maintenance systems that help keep those jumbo jets aloft.
But an increasing number of critics worry that this long safety record is in jeopardy.
That's because the repair and maintenance systems and the Federal Aviation Administration, which is responsible for inspecting them, are both in the midst of historic transformations.
A record amount of work is being outsourced to foreign and non-FAA-certified repair stations. At the same time, the FAA has a decreasing number of inspectors, forcing it to rely more on computer models instead of looking over mechanics' shoulders to check their work.
Depending on where one sits, the result is either an increasingly dangerous set of conditions or a triumph of the efficiencies of global economics and emerging technology.
The controversy, which includes concerns about possible terrorist infiltration of foreign repair stations, has prompted two federal investigations and hearings on Capitol Hill.
"If the American people understood some of the safety and security issues surrounding foreign repair stations, they would march on Washington with pitchforks," Sen. Claire McCaskill (D) of Missouri said during a hearing last week.
The nation's airlines have long outsourced some minor maintenance. The trend picked up during the 1990 and accelerated with the airlines' economic crisis that started in the spring of 2001 and continued after 9/11.
In 1996, private and foreign companies did 37 percent of the work. Today, that number is up to 64 percent. While the FAA has no data to indicate how much of that outsourced work is done abroad, the inspector general of the Transportation Department concluded that it's a significant amount.
Moreover, these outsourced companies aren't just changing the oil, according to the inspector general of the Transportation Department. They're now undertaking crucial repairs on things like landing gear.
At these foreign repair stations, critics note, workers aren't required to go through periodic drug and alcohol testing, or to undergo background checks. And some foreign repair stations are in countries that have active terrorist cells, such as the Philippines and Indonesia.
Critics see another serious safety problem with foreign repair stations: They don't get surprise spot checks by the FAA, the way domestic shops do. Instead, the foreign facilities are given 60 to 90 days' notice before an FAA inspector shows up.
Then there's the issue of uncertified foreign stations, whose number is estimated to be three times greater than that of certified foreign repair shops. A loophole allows them to still do work on US planes, as long as one FAA-certified mechanic signs off on the work.
"Safety is definitely being compromised," says Robert Roach Jr. of the International Association of Machinists and Aerospace Workers, which represents airline mechanics.
But the airlines, as well as FAA management, say that safety is not being compromised in any way. They note there hasn't been a major airline crash since November 2001, when American Airlines Flight 587 crashed in Queens, N.Y. They also note that the overall aviation accident rate continues to decline. Of those tragic few that do occur, they say, only 8 percent are maintenance-related.
"Safety is the constant, overriding imperative in our members' activities," said Basil Barimo of Air Transport Association, which represents major US carriers, during last week's hearing. "[The airlines] understand their responsibilities, and they act accordingly. The US airline industry's stellar – and improving – safety record demonstrates that indisputable commitment."
Or as Les Dorr, a spokesman for the FAA says: "Just because work is being done at a foreign repair facility does not mean it's unsafe at all – in fact, sometimes 180 degrees the opposite."
FAA management and the airlines note there are layers of redundancy to ensure safety. For example, in addition to the FAA-certified mechanics, the airlines' own mechanics check work when planes are returned. But during the hearing, Mr. Roach of the mechanics union said that what his members find sometimes is frightening.
"Our members have also seen aircraft return from repair facilities with the flaps rigged improperly, engine fan blades installed backwards, improperly connected ducting … and over-wing-exit emergency slides deactivated," he says. "These aircraft had all been deemed airworthy by the repair stations."
The union that represents the FAA inspectors has also raised alarms. They contend the FAA has not given them the resources to properly oversee all the work that's now been shifted overseas or to private facilities in the US. In addition, within the next five years, 50 percent of the current inspectors will be eligible for retirement.
To improve safety, the FAA has started relying more on data analysis to identify potential problems that can be inspected selectively. Some stations, however, go for months or years without proper oversight.
That, say inspectors, has put them in a difficult position. "Assuming good intent on everyone's part, things still happen.... It's just a matter of time," says Tom Brantley, president of the Professional Airways Systems Specialist, which represents FAA inspectors.