PHILADELPHIA — A key piece of hardware that aviation experts and pilots said could solve the mystery in the fatal crash of the medical transport Learjet on Jan. 31 turned out to be useless.

The NTSB's early investigation into the Jan. 31 crash revealed little about what caused the Learjet 55 to go down seconds after taking off from Northeast Philadelphia Airport. The jet slammed into ...

Photographs released by the National Transportation Safety Board (NTSB) show the extent of ground damaged caused by last week’s deadly crash of a Bombardier Learjet 55, and the state of the jet ...