WASHINGTON -- A computer problem at the Federal Aviation Administration (FAA) caused massive flight delays in the United States Tuesday.

     Because one of the FAA's two systems that process flight plans went down, delays could pile up at airports across the country, according to FAA chief operating officer Hank Krakowski.

     Delays up to 90 minutes are already surfacing at several airports. "This was a failure mode we have not seen before," Krakowski told reporters.

     According to the FAA, about 6,500 airplanes are in FAA system, though the aviation agency has not said how many were in the sky and how many were on the ground when the problem occurred.

     With such a heavy volume of air traffic typically converging on the East Coast, delays could spread depending on how much time it takes to iron out the problem.

     Krakowski said most of the delays were happening in the eastern portion of the United States, with none reported west of Dallas or Chicago.

     Boston is currently affected by the problem, while New York City area airports are not feeling its effects.

     In Chicago, the city's aviation department is also recommending travelers check the status of their flights before heading to the airport.

     At Washington D.C.'s Reagan National Airport, no major delays were