System Safety Terms and Concepts

An abort should only be set into motion by the issuance of a valid abort command from an authorized entity. This requirement is particularly germane to unmanned systems (UMSs). In a manned system, the authorized entity is generally the official operator however, in a UMS much planning must go into determining what constitutes a valid command and a valid controller (authorized entity) because it may be possible for an unauthorized entity to take control of the UMS. 

Concise Encyclopedia of System Safety Definition of Terms and Concepts, First Edition. Clifton A. Ericson II. 

Example 1 The pilot decided to abort the intended mission and return to base after one of the two engines on the aircraft failed. In this case, aircraft safety is reduced, and preestablished contingency plans require the pilot to terminate the mission rather than expose the aircraft to higher mishap risk and loss of the aircraft. In this situation, the pilot is the authorized entity. 

Example 2 An aircraft weapon system enters the abort state if any unsafe store conditions are detected in other states, and/or if any abnormal conditions that preclude completion of the normal initialization and release sequence occur. An abort command is issued to the store, and all station power is subsequently removed. If transition to the abort state occurs after the launch state has been entered (and irreversible functions have been initiated), power is removed from the store interface, and no further attempts to operate the store are conducted during the ongoing mission. In this case, the system itself is the authorized entity. 

Abnormal operation (of a system) is system behavior which is not in accordance with the documented requirements and expectations under normally conceivable conditions. Abnormal system operation is when a disturbance, or disturbances, causes the system to deviate from its normal operating state. The effects of abnormal operation can be minimal or catastrophic. 

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