A key safety system was turned off on the U.S. Army helicopter that collided with an American Airlines regional jet last week near Washington's Reagan Airport, killing 67.

A US Army helicopter collided with an American Airlines jet near Ronald Reagan National Airport, marking the deadliest disaster in 20 years.

An American Airlines jet hit an Army helicopter carrying three soldiers as the plane got ready to land at Reagan National. The two aircraft went into the Potomac River outside

Investigators revealed that the U.S. Army Black Hawk helicopter that collided with American Airlines Flight 5342 was flying about 100 feet higher than it should have been, and also stated the helicopter crew was warned about the incoming jet two times.

Air traffic controller audio TIME retrieved from LiveATC.net revealed what happened moments before the collision. The tower had cleared the plane for landing on Runway 33, but just seconds before the crash, an air traffic operator asked the helicopter—with radio call sign PAT 25—if the commercial jet—referred to as the CRJ—was in sight.

The female pilot killed in the helicopter collision with a passenger jet in Washington DC will not be named, the US Army said.