aborts are caused by loss of more than one main engine or failures
in other systems. Loss of one main engine while another is stuck
at a low thrust setting may also necessitate a contingency abort.
Such an abort would maintain orbiter integrity for in-flight crew
escape if a landing cannot be made at a suitable landing site.
aborts due to system failures other than those involving the main
engines would normally result in an intact recovery of vehicle and
crew. Loss of more than one main engine may, depending on engine
failure times, result in a safe runway landing. However, in most
three-engine-out cases during ascent, the orbiter would have to
be ditched. The in-flight crew escape system would be used before
ditching the orbiter.