Direct methods of stability analysis have been intensely investigated over the past two decades and are now found practicable in obtaining accurate critical breaker clearing times for a given fault. Obtaining this information on-line is only an indirect way of ascertaining robustness of the system. In this paper we propose to convert this information into more realistic criteria such as simultaneous interchange capability (SIC) or maximum load capability (LSC) of the system subject to the system surviving the contingencies in a transiently stable manner. A fast transient stability algorithm combined with sensitivity of the energy margin to the LSC or SIC is proposed. Verification of the methodology on a 10-machine system lends confidence in this technique as a tool for dynamic security assessment.