American Airlines grounded its fleet of Boeing MD-80s on Wednesday so crews could reinspect wire bundles to comply with Federal Aviation Administration (FAA) regulations. The nation's largest carrier canceled more than 340 flights — or about 14 percent of its scheduled service — according to the latest results from FlightStats.com.

The need for the new inspections became known during an audit of American by a joint team of inspectors from the FAA and the Fort Worth-based airline.

“Preliminary results of the audit show a high rate of airworthiness-directive compliance,” Alison Duquette, FAA spokesperson in Washington, D.C., told msnbc.com.

As part of the audit, American grounded 80 MD-80s — out of a fleet of 204 — to check for compliance with its wiring, Duquette said.

“While the airline accomplished the work outlined in the airworthiness directive, inspectors raised concerns about the intervals at which certain wire bundles were secured. American decided to reinspect the affected aircraft — and are doing that now.”

American Airlines said it is ensuring the wiring was installed and secured properly.

The inspection involves proper spacing between two bundles of wires in the plane's auxiliary hydraulic system. It must be installed "exactly according to the directive", American Airlines spokesperson Tim Wagner said.

“We are in the process of completing the inspections on the remaining airplanes and will return them to service on a rolling basis throughout the day,” Wagner said.

Wagner said of the 80 planes that the airline decided needed modification, about 20 have returned to flying and that no Thursday flights had been canceled as of Wednesday evening.

About 85 departures were canceled at American's Dallas-Fort Worth hub and another 68 were grounded at Chicago's O'Hare.

Meanwhile, Delta Air Lines said it was voluntarily reinspecting wiring on 133 MD-88 and MD-90 airplanes. However, it had no estimate Wednesday on how many flights it might need to cancel, a spokeswoman said.

Delta said its 117 MD-88 and 16 MD-90 planes were inspected earlier this year but the airline is "proactively and voluntarily revalidating" compliance with a directive from the Federal Aviation Administration.

The review is expected to be completed by Saturday, and the Atlanta-based airline is contacting passengers whose flights might be canceled in order to rebook them on other aircraft, spokeswoman Katie Connell said.

Earlier this month, Southwest Airlines grounded 43 of its planes to examine if they were structurally sound enough to carry passengers. The move came after the low-cost carrier admitted it missed required inspections of some planes for cracks.

The FAA is seeking a record $10.2 million civil penalty from Southwest after the carrier continued to fly nearly 50 planes after it told regulators it had missed the required inspections.

FAA feels the heat
The FAA, meanwhile, has recently come under fire.

“The complacent attitude we've seen from President Bush's FAA has led to many problems across the aviation industry — from unsafe runways and major flight delays to an insufficient number of safety inspectors and trained air traffic controllers,” Sen. Frank R. Lautenberg, D-N.J., a member of the Committee on Commerce, Science and Transportation, said Wednesday. “It shouldn't take uninspected planes loaded with passengers to get the FAA and the airlines focused on safety. They should be focused on passenger safety all the time — without exception.”

Video   American grounds MD-80s March 26: American Airlines voluntarily canceled about 10 percent of its flights across the U.S. so it can inspect the wiring in the fleet's MD-80 aircraft. NBC's Jay Gray reports. MSNBC

Following Southwest Airlines' inspection deficiencies, acting FAA Administrator Robert A. Sturgell called the events “a twofold breakdown in the aviation system” — first, Southwest's failure to properly inspect its planes; and the FAA's failure to ground the jets as “at least one FAA inspector looked the other way.” The $10.2 million penalty is the largest the FAA has ever imposed on a carrier. Southwest has said it will appeal.

Rep. James Oberstar, chairman of the Transportation and Infrastructure Committee, suggested earlier this month that the FAA should “clean house from top to bottom” and has too cozy a relationship with the airlines.

Oberstar also said he believed similar violations may have occurred involving other airlines, but that those who have such evidence are afraid to come forward.

The Associated Press contributed to this report.

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