Definition of "unstart"

Jim Eastham, one of the original SR-71 test pilots, vividly remembers unstarts: “An unstart demands your full and undivided attention,” he recalls.

1988 November, T. A. Heppenheimer, quoting Jim Eastham, “Mach 5 spy plane”, in Popular Science‎, volume 233, number 5, page 114

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.

1996, Richard H. Graham, “Technical Features of the SR-71”, in SR-71 Revealed: The Inside Story‎, Zenith Imprint, Unstarts and Aerodynamic Disturbances (ADs), page 56

At supersonic speeds, adverse interactions between shock waves and boundary layers can increase drag and cause engine unstart.

2006, National Research Council (U.S.). Steering Committee for the Decadal Survey of Civil Aeronautics,, Decadal Survey of Civil Aeronautics: Foundation for the Future‎, National Academic Press, Appendix A: R&T Challenges for Aerodynamics and Aeroacoustics, page 73