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.

An American Airlines regional jet was involved in a midair collision near Washington, D.C., the Federal Aviation Administration said Wednesday.

An NTSB-led investigation is in full swing to identify factors that led to the Jan. 29 midair collision between an American Eagle Bombardier CRJ-700 operated by PSA Airlines on approach to Ronald Reagan Washington National Airport (DCA) and a U.S. Army Sikorsky UH-60L Black Hawk helicopter.