An NTSB investigator looking at a plane crash. My memory of some of this is hazy. This movie had very odd elements, like him dreaming about being in a plane and seeing cracks developing in the body of the plane. Also, finding an extra arm. Turns out that he's on the plane that crashes.
It might be the 1989 film Millennium (based on the John Varley short story “Air Raid”). The main character is an NTSB investigator who is looking into an air accident, and some strange things are happening.