WASHINGTON, July 30 (Reuters) -

The National Transportation Safety Board said on Wednesday

that testing showed faulty altitude data in U.S. Army

helicopters like the one that collided with an American Airlines ( AAL )

plane on January 29, killing 67 near Ronald Reagan

Washington National Airport.

The NTSB investigative hearing is looking at the military

aircraft's air data systems and altimeters as well as the

Federal Aviation Administration's oversight of Washington

airspace and air traffic.

The crash -- a half-mile southeast of the airport over the

Potomac River -- was the deadliest U.S. air disaster in more

than 20 years. Testing showed that Army helicopters in flight

showed discrepancies of 80 to 130 feet versus actual altitude.

The NTSB played audio excerpts of communications between

air traffic control towers during the minutes before the crash

including a request by controllers to the American Airlines ( AAL )

plane to shift to a different runway.

Previously, the NTSB said the helicopter's altitude was

higher than it should have been for the area at the time of the

crash.

The maximum altitude for the route the helicopter was

taking was 200 feet but the collision occurred at an altitude of

around 300 feet.

The Black Hawk, which was on a nighttime training

flight, had a crew of experienced pilots wearing night vision

goggles.

In May, the FAA barred the Army from helicopter flights

around the Pentagon after a May 1 close call that forced two

civilian planes to abort landings. The FAA this week said the

helicopter flights remained on hold even after the agency

disclosed it had signed a new agreement with the Army on July 1.