Defense Secretary Pete Hegseth announced the Pentagon has begun a probe into the cause of a deadly midair collision between a passenger jet and a military helicopter, looking to understand who was to blame and how the tragedy occurred.

Among the unanswered questions about the crash near Washington, D.C., are the flight pattern of the Black Hawk helicopter and the exact nature of its training exercise.

Pete Hegseth, chief of the Defense Department, announced Thursday that the Pentagon and Army are investigating the collision over Ronald Reagan Washington National Airport in an unexpected first test for the newly minted secretary.