WATCH: Helicopter crew in DC collision may not have heard key instruction from tower, NTSB says

WASHINGTON (AP) — The crew of the helicopter that collided midair with an American Airlines jet near Washington D.C.’s Ronald Reagan National Airport might not have heard instructions from the air traffic controller to pass behind the plane, investigators said Friday.

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National Transportation Safety Board Chairwoman Jennifer Homendy said the recording from the Black Hawk helicopter cockpit suggests the crew may have missed the key instruction just before the Jan. 29 collision, in which all 67 aboard the two aircraft were killed

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Homendy said the helicopter was on a check flight that night when the pilot was being tested on the use of night vision goggles and flying by instruments. Investigators believe the crew was wearing night vision goggles throughout the flight.

The collision was the deadliest plane crash in the U.S. since 2001, when a jet slammed into a New York City neighborhood just after takeoff, killing all 260 people on board and five more on the ground.

Homendy said the Black Hawk crew never heard the words “pass behind the” during the transmission from the controller because the helicopter’s microphone key was depressed right then.

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At one point during the flight before the collision the helicopter’s pilot called out that the Black Hawk was at 300 feet, but the instructor pilot said the helicopter was at 400 feet, Homendy said.

“At this time we don’t know why there was a discrepancy between the two,” Homendy said.

Sullivan reported from Minneapolis.