A sudden compressor stall that can occur in the jet engines of supersonic aircraft.
1988, T. A. Heppenheimer, Mach 5 spy plane, Jim Eastham, one of the original SR-71 test pilots, vividly remembers unstarts: “An unstart demands your full and undivided attention,†he recalls.
1996, Richard H. Graham, SR-71 Revealed: The Inside Story Chapter Technical Features of the SR-71, An unstart was usually a very unpredictable and violent manoever of the aircraft. ... At altitudes above 75,000 feet, aileron control may in ineffective in controlling the roll during an unstart unless the Angle of Attack is immedicately reduced. the instant an unstart occurs, the pilot's first action is to arrest any pitch-up motion of the aircraft.
2006, National Research Council (U.S.). Steering Committee for the Decadal Survey of Civil Aeronautics,, Decadal Survey of Civil Aeronautics: Foundation for the Future, At supersonic speeds, adverse interactions between shock waves and boundary layers can increase drag and cause engine unstart.
