The deadliest plane crash in U.S. history was in May 1979, when American Airlines Flight 191 lost an engine during takeoff at Chicago O’Hare International Airport and crashed moments later, killing 258 passengers and 13 crew. Two people on the ground also were killed.

Investigators trying to determine what caused last week’s deadly midair collision between a US military Black Hawk helicopter and an American Airlines plane near Washington, DC, briefed lawmakers Thursday on what they’ve learned after combing through data from both aircraft and air traffic control.

Investigators searching for wreckage from last week’s deadly midair collision between a US military Black Hawk helicopter and an American Airlines plane near Washington, DC, conducted an overnight scan of the Potomac River where the aircraft fell using advanced imaging technology to map the riverbed and locate debris.

American Airlines aircraft and US Army helicopter collided in mid-air in Washington DC. Investigators recovered all of the victims in the Potomac River

The wreckage of the Black Hawk helicopter that collided with an American Airlines plane over the Potomac River in Washington DC has been removed from the crash site and is being examined by the National Transportation Safety Board.

The black hawk helicopter involved in the deadly collision with an American Airlines jet over Washington, D.C. has a crucial safety system turned off at the time.