The bondholders' agent, U.S. Bank, is expected to argue at a Thursday hearing in U.S. Bankruptcy Court in Manhattan that the airline unit of AMR Corp has neglected its planes, and failed to make hundreds of repairs.
They fear that this and other costs could force the value of the planes to sink too low to cover the bonds.
The value "will continue to erode as a result of the costs to insure, store, ferry, market and sell the aircraft," U.S. Bank said in court papers.
Most of the planes are older-model aircraft, including Boeing 757s and MD-82s and MD-83s made by McDonnell Douglas. Payment on the bonds is due Oct. 15.
Sean Collins, a spokesman for American Airlines, on Wednesday disputed the bank's claim, saying there has been "no change in American Airlines' maintenance policies and procedures that would impact the value of the aircraft."
U.S. Bank is seeking to bolster safeguards for the bonds under bankruptcy rules designed to protect secured creditors from declines in the value of collateral.
It wants to file a top-priority bankruptcy claim to ensure bondholders are paid ahead of other creditors, to offset any decrease in value from AMR's alleged delay in making nearly 500 repairs to cabins, engines and plane structures.
U.S. Bank believes it would fetch just $501 million - including $40 million of previously frozen cash collateral to which it seeks access - if it seized and sold the planes. That's barely above the $491 million in principal and interest that it said bondholders are owed.
But AMR said in court papers that U.S. Bank's request "borders on -- if not crosses the line of -- being frivolous."