20 of the 50 A-12/SR-71 airframes were lost over 25 years, a high ratio indeed, but remarkably only four crew died. One was unable to separate from his seat after ejecting, another drowned after opening his visor following ejection and a sea landing. The reasons for the losses were many; mid air collisions, landing accidents, instrumentation and wheel failures, etc - only one appears to have definitely been caused by an engine unstart.