The staffing at the air control tower at Reagan National Airport was "not normal" when an American Airlines plane and Army helicopter collided on Wednesday night, a report shows.

U.S. authorities said on Thursday it was not yet clear why a regional jet crashed into a U.S. Army helicopter at a Washington airport, killing 67 people in the deadliest U.S. air disaster in more than 20 years.

Investigators analyze flight data to understand the crash between an American Airlines jet and a military helicopter and exactly what was going on before disaster struck.

Ronald Reagan Washington National Airport (DCA) services both military helicopters and passenger planes every day.

The airspace around Ronald Reagan Washington National Airport has long been problematic due to heavy military and commercial flight activity in the nation’s capital, according to industry insiders.

WASHINGTON D.C., DC — Multiple Texas representatives have released statements Wednesday night after a plane collided with a military helicopter, causing it to crash near the Ronald Reagan Washington National airport. Ronald Reagan Washington National airport has closed all runways, and stopped air traffic in the area.

According to the Patrick Leahy Burlington International Airport website, three American Airlines flights between DCA and BTV were canceled for Wednesday night and Thursday morning.

Ronald Reagan Washington National Airport is closed, according to an FAA alert posted Wednesday night. A ground stop will prevent planes from landing at the airport through at least 5 a.m. Thursday morning,

Authorities are investigating an apparent crash involving a regional jetliner and a helicopter

DCA is one of the most demanding airports in the world. It also has what’s known as ‘helicopter alley’ with hundreds of police, military, news and rescue helicopters criss-crossing

A preliminary safety report from the Federal Aviation Administration reportedly found that air traffic control staffing was abnormally low at Ronald Reagan Washington National Airport on the evening of Wednesday, Jan. 29, according to The New York Times, which obtained a copy of the report.