The NTSB has cleared the Sport-Jet prototype, which crashed in June during flight testing in Colorado Springs, Colo. While the accident remains under investigation, the NTSB’s preliminary report shows that the aircraft had no mechanical failures. Officials at Excel-Jet, which is developing the jet, believe the cause of the accident was wake turbulence. A Dash 8 turboprop took off just before the prototype. The single-engine, four-place personal jet will sell for about $1 million.