explosion. as soon as it cleared our view, line of site, a ball of flames shot up higher than the apartments. reporter: firefighters rushed to the scene. flames shot out of several floors. windows blown out by the impact an explosion. fox news confirms the pilot is joseph andrew stack and he is dead. federal officials are investigating whether he crashed the plane into the building intentionally. federal agents are looking into a message on the web site where he goes on and on about problems with the irs. i want to assure the citizens of austin, texas, they are safe. there is no danger. the situation is contain. reporter: six miles away from the crash site, firefighters battling this house fire. neighbors say this was stack s home. norad scrambled two f-16 jets over the area. the president was briefed on the incident. at least one person that worked in the building is unaccounted for. two others are in the hospital. more trouble in the air. a bomb threat forced a