An American Airlines flight operated by PSA Airlines was involved in a midair collision with a military helicopter on Wednesday night near Washington, D.C.

The American Airlines’ subsidiary has ties that go back decades in Ohio, and just said it was moving its headquarters to Charlotte.

American Airlines CEO Robert Isom said that Flight 5342 was on a normal approach to Reagan National Airport and that “we don’t know why the military aircraft came into the path of the PSA aircraft,” one of the many questions the Fort Worth-based carrier is asking in the wake of the tragedy that took 67 lives.

D.C. police confirmed a crash had taken place over the Potomac and that search and rescue operations were taking place in the river. Donald Trump later weighed in.

American Airlines Group Inc. (NASDAQ: AAL) owns PSA, which already has a large presence in Charlotte, operating regional flights on American’s behalf. American is based in Fort Worth, Texas, but runs its second-largest hub at Charlotte Douglas, known as CLT.

“A PSA Airlines Bombardier CRJ700 regional jet collided in midair with a Sikorsky H-60 helicopter while on approach to Runway 33 at Reagan Washington National Airport around 9 p.m. local time,” the Federal Aviation Administration (FAA) said in a statement.

American Airlines CEO Robert Isom on Thursday morning expressed his condolences to the family and loved ones of those aboard a flight that collided with a military helicopter Wednesday night.

US airlines had gone 16 years without a fatal crash until Wednesday night. But as impressive as that safety record had been, there have been warning signs in recent years of a significant risk of a collision like the one that just killed 67 people.

Wednesday night’s crash of an American Airlines commuter plane in Washington could be one of the worst disasters for the Fort Worth-based airline in more than two decades.

Both the captain, Jonathan J. Campos, 34, and co-pilot, Sam Lilley, 28, had been flying for years, according to family and friends.

The American Airlines flight was operated by PSA Airlines, which still has its corporate headquarters at Dayton International Airport but will soon be moving to Charlotte.