WASHINGTON — The crew of the Army helicopter that collided with an American Airlines jet may have had a malfunctioning altimeter that did not accurately display its altitude, National Transportation Safety Board Chair Jennifer Homendy said Friday during a briefing about the Jan. 27 crash that killed 67 people aboard both aircraft.

About three minutes before the aircraft collided, the helicopter pilot reported being at 300 feet while the instructor pilot indicated they were at 400 feet, Homendy said.

“Neither pilot made a comment discussing the altitude discrepancy,” Homendy said as she detailed the final 17 minutes on board both aircraft. “We don’t know why there was a discrepancy between the two.”

Two minutes after the two pilots reported different altitudes and about two minutes before the collision, the instructor pilot reiterated they were at 300 feet and needed to descend. The pilot indicated they would do so.

About 17 seconds before impact, the cockpit voice recorders on both aircraft recorded a radio transmission from the air traffic control tower that the Black Hawk helicopter should pass behind the plane.

“The cockpit voice recorder from the Black Hawk indicated the portion of the transmission that stated 'pass behind' may not have been received by the Black Hawk crew,” Homendy said, adding that the helicopter was setting up its microphone to communicate with air traffic control at the time.

About seven seconds before the crash, the Black Hawk instructor pilot told the pilot they believed air traffic control was asking it to move left toward the east bank of the Potomac River.

The NTSB is currently conducting a visibility study to determine what the pilots were able to see during the flight, but Homendy said it is unlikely that the personnel inside the helicopter knew a crash was impending.

Based on the nose of the American Airlines plane at the time of impact, the pilot of the jet attempted to avoid the helicopter, the NTSB said. Flight recorder data indicates the plane was “near maximum nose-up travel” one second before impact.

Homendy said the night vision goggles the helicopter crew were wearing at the time of the crash could also have been an issue.

The helicopter crew was conducting an annual night vision goggle check ride. The agency believes the crew was wearing the goggles at the time of the collision because its members would have been required to have a discussion about removing them, and there was no evidence that happened on the cockpit voice recorder investigators retrieved after the crash, Homendy said.