This abort mode is adopted when there is a loss of more than one engine or due to system failures. Abort mode permits crew escape when landing of the shuttle cannot be achieved at a suitable landing field.
There is a definite order of preference for the various abort modes. The type of failure and the time of the failure would determine which type of abort is selected. In most cases where performance loss is the only factor, the preferred modes would be ATO, AOA, TLA and RTLS. For certain support system failures, such as cabin leaks or vehicle cooling problems, the preferred mode might be the one that would end the mission quickly. In these cases, TLA or RTLS will be preferable to AOA or ATO. A contingency abort would never be chosen if another abort option exists.