By THE ASSOCIATED PRESS

Rigorous airline maintenance audits recently ordered by federal regulators are likely to yield the most headaches for travelers flying Northwest, American and United airlines. Those carriers have the oldest fleets, on average. The older the jet, the more likely it requires time-consuming, and potentially flight-grounding, government-ordered inspections, analysts and regulators agree. ''Older planes will usually have more (airworthiness directives) simply because they've been around longer,'' said Federal Aviation Administration spokesman Les Dorr. Northwest Airlines Corp.'s fleet of roughly 350 planes has the oldest average age at nearly 18 years old, followed by AMR Corp.'s American Airlines at 15 years, and UAL Corp.'s United Airlines at 13, according to the companies' most recent annual reports. ''We don't have any concerns related to the age of the fleet,'' said Northwest spokeswoman Tammy Lee, adding that the carrier is retiring about 10 of its oldest aircraft this year. Northwest is well positioned to pass the current review, having gone through a rigorous FAA maintenance oversight process after a mechanics strike in 2005, Lee said. Showing compliance with this FAA audit is ''a voluminous process ... (but) a procedural issue and record-keeping issue,'' she said. Reports of shorted wires, evidence of worn-down power cables, and fuel system reviews conducted by the manufacturer, Boeing Co., led to the airworthiness directive on the MD-80 aircraft that were grounded last week by American, Alaska Airlines and other carriers, inconveniencing hundreds of thousands of travelers. That government order carried an effective date of Sept. 5, 2006, and airlines had 18 months to comply. The first round of FAA audits over a two-week span last month — prompted by revelations that Southwest Airlines Co. flew dozens of planes that had missed inspections — checked 10 airworthiness directives that apply to each carrier's fleet. The second phase, which runs through June 30, will check 10 percent of the orders that apply to each airline's fleet.
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