American Airlines CEO Robert Isom said the National Transportation Safety Board, which is investigating the deadly midair collision between an American passenger jet and a military helicopter, will be the lone authority on the cause and details of the crash.

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.