An inspector general's report says the Federal Aviation Administration is experiencing substantial delays and cost overruns in a key component of its effort to modernize the U.S. air traffic control system.

The inspector general, Calvin L. Scovel, is concerned with a computer program that manages planes at high altitudes.

The program is critical in the FAA's effort to move to GPS technology for tracking airplanes.

Scovel said in a letter to lawmakers that more than 200 problems were found with the program, prompting a temporary halt on further testing. Although the FAA has resumed testing and says progress is being made, updated software has exhibited new problems and old ones.

The computer woes will force the FAA to maintain aging equipment longer than planned and retrain air traffic controllers.