Shortly before sunrise on Jan. 23, 2009, passengers on US Airways Flight 518, who were flying from Omaha to Phoenix, were startled by a terrifying shriek.

The pressure seal around the main cabin door was failing, and that shriek was the sound of air leaking through. The plane diverted to Denver. Everybody was safe.

But that and other recent malfunctions affecting US Airways planes, which NPR is reporting for the first time, raise questions about a controversial and growing practice at most U.S. airlines: The industry is sending 1 of every 5 planes to developing countries, from Central America to Asia, when the planes need to be overhauled and repaired....The globalization of airline maintenance is a remarkable reversal. Until just a few years ago, America's airlines maintained most of their own planes. The FAA requires airlines to overhaul every plane roughly every two years or less, and small armies of mostly union mechanics at the airlines did the work.

But that was before 2002 — when US Airways filed for bankruptcy, American Airlines slashed flights, and other airlines teetered at the brink. Since then, airlines have been trying to survive by cutting back on any expenses they can control — including the little bags of peanuts.

One of the biggest areas airlines can cut costs is maintenance. Consider this: If an airline fixes its own planes in the U.S., it spends up to $100 per hour for every union mechanic, including overhead and other expenses, according to industry analysts. The airline spends roughly half as much at an independent, nonunion shop in America. And it spends only a third as much in a developing country, such as El Salvador...Industry analysts say there are roughly 700 FAA-approved repair companies in other countries — including repair shops in Argentina, Costa Rica, Ethiopia, Kenya, China and Indonesia. The Aeroman company in El Salvador is becoming one of the more popular, drawing business from US Airways, JetBlue, Frontier, Southwest and other U.S. carriers.

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But the inspector general at the Department of Transportation has investigated those checks and balances and has repeatedly warned over the past six years that FAA and industry inspectors are not monitoring the work the way they should. His reports are written in the dry bureaucratic language of Washington, D.C., but they add up to a scathing critique of the way the FAA monitors the foreign repair industry — or fails to. For instance, his 2008 report declared:

"FAA still does not have comprehensive data on how much and where outsourced maintenance is performed."

Translation: The FAA does not require airlines to report exactly where they send their aircraft for which kinds of repairs. So, FAA inspectors are not sure which of the roughly 700 foreign repair shops they should inspect.

"There is no standard for all FAA offices regarding initial inspector visits, which can cause safety issues to go unchecked."

Translation: The FAA's inspectors didn't even show up at some foreign repair stations to monitor their work for as long as three to five years.

"Problems existed [at foreign repair stations that the inspector general investigated], such as untrained mechanics, lack of required tools and unsafe storage of aircraft parts."

FAA officials told the inspector general they would correct those problems. "He has made recommendations that FAA improve its oversight, and we take those recommendations seriously," says Gilligan of the FAA.

But so far, FAA officials have not put those changes in place.

"These findings are very, very disturbing," says John Goglia, a former presidential appointee on the National Transportation Safety Board. "We don't know what's going on in those facilities [foreign repair companies]. If we're not monitoring them properly, how do we know it's safe?"

But that and other recent malfunctions affecting US Airways planes, which NPR is reporting for the first time, raise questions about a controversial and growing practice at most U.S. airlines: The industry is sending 1 of every 5 planes to developing countries, from Central America to Asia, when the planes need to be overhauled and repaired....The globalization of airline maintenance is a remarkable reversal. Until just a few years ago, America's airlines maintained most of their own planes. The FAA requires airlines to overhaul every plane roughly every two years or less, and small armies of mostly union mechanics at the airlines did the work.