Airline officials said late Thursday that they had come up with a fix for the seats, and began pulling 48 Boeing 757s out of service to make repairs. All the planes should be back in service by Saturday.
Those planes use the same model of seat that came loose on three recent American Airlines flights involving 757s that had been recently refurbished. The seats had been removed and reinstalled as part of the work.
American originally said the problem was due to a clamp that holds rows of seats to tracks on the aircraft floor.
But officials offered a new explanation Thursday, saying that a combination of wear, poor design and even soda spilled into the tracks caused pins to pop out of the grooves.
The airline has used the same seat on its planes for 20 years without incident until now, said David Campbell, American's vice president of safety.
"The fundamental design of this seat is not as robust as some of the latest designs," Campbell said in an interview.
Campbell said the new fix will consist of installing an additional locking mechanism that was designed by American's engineers and approved by the Federal Aviation Administration.
It will take crews four to six hours to fix each plane. The airline began stopping 757s as they landed Thursday and taking them out of service.
Figures from FlightAware.com show that American canceled 62 flights after noon EDT on Thursday and 59 were 757s. For Friday, the airline has already canceled 23 flights including 19 by 757s, according to the flight-tracking service.