FORT WORTH, Texas (AP) _ American Airlines crews had to inspect and test the exit slides on about 270 aircraft last week.
Fort Worth-based American says a mechanic discovered a problem with the way the slides had been packed and stowed.
American says it replaced the rear emergency slides on 11 jets due to unusual wear.
The slides were working on all of the MD-80 jets.
But American spokesman Tim Wagner says the slides had been packed and stowed on the planes without using a tool recommended by the manufacturer.
The tool is meant to prevent the inflation tube from getting crushed.
Wagner says the 11 slides that were replaced had potential issues, but none failed to inflate.
A Federal Aviation Administration spokeswoman says any maintenance violation could potentially result in an enforcement case. She would not comment on whether a case had been opened in this instance.