What went wrong with the MD-80 aircraft?

As it turns out, the American Airlines cancellations that began on April 8, 2008, are directly related to a March 2008 incident with an entirely different airline. On March 6, the Federal Aviation Administration (FAA) levied a record $10.2 million fine against Southwest Airlines for allowing 47 of its Boeing 737 aircraft to remain in operation without proper inspections [source: Bloomberg].

The enormous fine rippled through the airline industry. Most carriers have MD-80s in their fleets, and the issue with Southwest's planes held true for all MD-80s. The aircraft are aging -- American Airlines (AA) said at the time of the April cancellations that the average age of its MD-80 was 18 years [source: Los Angeles Times]. When the FAA found that Southwest had failed to comply with a separate order to inspect its 737s, the federal agency announced that it would conduct unscheduled inspections of MD-80 aircraft owned by more than 100 U.S. carriers [source: Bloomberg]. As a result, many airlines began canceling flights in order to check or double-check the wiring on their planes.

At issue is the wiring that electrifies the planes' auxiliary hydraulic systems, which in turn powers some aircraft components. The problem isn't necessarily with the functionality of the wiring. The FAA's airworthiness directive -- an order to complete an inspection or work on an aircraft -- includes an engineering change order pertaining to the spacing of the wire bundles. The bundles are meant to be exactly 1 inch apart, secured to the wall of the plane's wheel well and properly covered [source: Bloomberg]. Sounds like a simple enough order, but the instructions came in a 38-page handbook and American Airlines told Aviation.com that its engineers may have had some trouble deciphering it [source: Aviation]. It was this confusion that compounded the massive cancellations while American Airlines inspected half its total fleet of jets for compliance [source: CBC].

In a statement issued on April 8, 2008, AA assured the public that the situation with the wiring wasn't a dangerous one; there was no problem with the safety of its planes [source: AA]. This echoes a similar sentiment from an American Airlines spokesperson shortly after the airworthiness order was issued and the inspections began in March. The spokesperson said the inspections were "an abundance of caution" on the airline's part [source: Bloomberg].

The Allied Pilots Association (APA) union pointed out, however, that these wiring bundles were located near the fuel tanks. A shorted wire could cause an electrical arc, which could ignite jet fuel fumes, potentially creating an explosion in the fuel tanks. It was for this reason, the APA said, that the FAA issued the airworthiness directive [source: Los Angeles Times].

There have been other problems with the MD-80 in the past. In 2000, airlines canceled flights when it came to light that there may be troubles with the jackscrew assembly -- a long bolt that controls the horizontal movement of the tail. An Alaska Airlines MD-80 crashed, killing 88 passengers [source: CNN], and inspectors found that the airline had been greasing the jackscrew every 2,550 hours in the air instead of the required 650 flight hours [source: The Avion]. The findings set off a wave of inspections similar to those seen in April 2008.

In the midst of the aircraft inspections in March and April 2008, CNN reported that there had been a series of recent in-flight troubles with the MD-80. The report stated American Airlines' MD-80s experienced 23 recorded landing gear malfunctions in "the last few months" [source: CNN].

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