Their business plans differ in many ways, but there's one area where major airlines and their cut-rate competitors agree: maintenance is a lot cheaper when it's performed by lower-paid mechanics working for outsourcers.

JetBlue, Southwest, America West, Northwest and United are among the carriers who outsource major maintenance of their aircraft to contractors in other countries, according to a report in The Wall Street Journal.

• As JetBlue's new A320 Airbus fleet ages, aircraft are sent to a repair hub in El Salvador;
• America West also sends its jets to El Salvador;
• Southwest has always outsourced its major maintenance;
• US Airways mechanics agreed Friday to pay cuts and the outsourcing of 2,000 mechanics jobs;
• Northwest sends its wide-body jets to Singapore and Hong Kong;
• Bankrupt United Airlines recently won union approval to begin using outside contractors for heavy maintenance.

It wasn't long ago that major airlines employed their own highly-skilled mechanics, each with his or her own Federal Aviation Administration license. The mechanics, who often studied for two years before taking the test, could make $60 or more per hour.

Mechanics working for outsourcers don't have to be licensed. Only supervisors are required to hold FAA licenses and are responsible for oversight of the mechanics, who in countries like El Salvador may make $10 to $20 per hour.

Is this endangering long-term safety of the U.S. commercial fleet? The airlines say no but others aren't sure.

Last year, investigators found that deficient maintenance by an outside vendor was partly to blame for the 2003 crash of a commuter flight in Charlotte, N.C. that killed 21 people.

In 1999, ValuJet flight 592 crashed into the Florida Everglades after taking off from Miami International Airport, killing all 110 on board. The crash was attributed to oxygen canisters improperly stowed in the aircraft's hold by maintenance employees working for an outside contractor.

In 2003, the Department of Transportation's Inspector General said the FAA was inadequately supervising outside contractors while devoting too many of its resources to oversight of in-house maintenance operations.

Airline spokesmen contend that the overseas maintenance contractors are more tightly supervised than the airlines' own mechanics. After all, the argument goes, they work on aircraft from airlines around the world and are subject to supervision by major European and Asian governments.

American Airlines says it prefers to keep heavy maintenance in-house because it has a well-trained, highly seasoned workforce. It outsources only 20% of its maintenance and none of its heavy tear-downs.