The term 'FAST PLANE' can be broken down into two crossword solutions: JET (3 letters) and SST (3 letters). A JET is a type of aircraft that uses JET engines to generate thrust. It is the most common type of aircraft used for commercial air travel. The Concorde, or the Supersonic Transport (SST), was a supersonic passenger airliner that flew from 1976 to 2003. It was the first commercial aircraft to fly faster than the speed of sound.