American initially put the number of cancellations at 200, but spokesman Tim Wagner said the estimate grew as the day progressed because the airline prefers to hold off on cancellations as long as possible. The entire fleet of MD-80s was being inspected, Wagner said.
Separately, Delta Air Lines said it was voluntarily re-inspecting 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.
At American, the need for the new inspections became known during an audit of the carrier by a joint team of inspectors from the Federal Aviation Administration and the Fort Worth-based airline, Wagner said.
The inspection involves proper spacing between two bundles of wires in the plane's auxiliary hydraulic system, Wagner said. It must be installed "exactly according to the directive," he said.
Of the 80 planes that the airline decided needed modification, about 20 have returned to flying, Wagner said. He said no Thursday flights had been canceled as of Wednesday evening.
"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.
About 85 departures were canceled in Dallas-Fort Worth and another 68 were grounded in Chicago, Wagner said.
Meanwhile, 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.
Shares of American's parent AMR Corp. fell $1.02, or over 10 percent, to close at $8.61 Wednesday, approaching the lower end of their 52-week range of $8.38 to $34. Delta's shares fell $1.23, or more than 12 percent, to $8.74, also nearing the cheaper end of their 52-week range of $8.61 and $23.25.
