The MD-80 series, a workhorse family of airplanes at the center of a growing maintenance problem for American Airlines, has been involved in two deadly crashes overseas and the carrier's most serious mid-air emergency in recent months.

The twin-engine plane began life as a modified version of the DC-9, entering service in October 1980. Boeing Corp., which later bought the aircraft's original manufacturer, McDonnell Douglas Corp., quit selling the plane in 1999.

AMR Corp.'s American Airlines is the world's largest operator of MD-80s, although the planes are also used by Delta Air Lines Inc., Alaska Airlines, Allegiant Air and numerous carriers abroad. Despite their relative age and lower fuel milage, the planes make up nearly a third of American's fleet.

"It's a ubiquitous single-aisle domestic airliner," said Robert Mann, an airline consultant who was involved in American's fleet planning when it first decided to use the plane. "Over time, it's obviously been an airplane American liked."

American mostly uses the planes on mid-range routes from hubs in Chicago and Dallas. The Fort Worth, Texas-based carrier canceled more than 1,000 flights Wednesday to re-inspect wire bundles in the planes' landing gear wheel wells. Alaska also canceled flights to check the wires.

The carriers renewed their inspections following Federal Aviation Administration audits involving multiple types of aircraft. The agency is stepping up maintenance reviews after acknowledging its inspectors were too lax last year with Southwest Airlines Co.

Les Dorr, a spokesman for the FAA, said problems with the MD-80 wires "could make the plane lose auxiliary hydraulic power or maybe cause a fire in the wheel well of the airplane."

An FAA airworthiness directive that is the basis for the inspections said the checks "are also intended to reduce the potential of an ignition source adjacent to the fuel tanks, which ... could result in a fuel tank explosion and consequent loss of the airplane."

The airlines contend the wires in question pose no threat to safety.

"This may be not so much a safety issue, just somebody wanting to have something done in a black-and-white fashion when before it was more of a gray area," Mann said.

The National Transportation Safety Board lists 36 accidents and other incidents involving MD-80s over the past five years.

On Sept. 16, an MD-82 operated by Orient Thai Airways overran a runway upon landing in heavy rain in Phuket, Thailand, killing 89 passengers and crew. One and a half months later, an Atlasjet MD-83 crashed on approach to Isparta Airport in Turkey, killing 57.

In late September, an American Airlines MD-82 jet carrying 138 passengers was forced to turn back shortly after takeoff in St. Louis when an engine fire broke out. On approach, the nose landing gear did not extend and the crew had to lower the gear using an emergency backup procedure, according to an NTSB report. Everyone aboard got off the plane safely.