Complexity makes the details of automation more difficult for the human operator to understand, model, and remember when that understanding is needed to explain automation behavior. Those humans can function effectively, however, only if the system is designed and structured to assist them to accomplish the required tasks. As technology continues to advance, it will become increasingly urgent that its applications on the flight deck be designed specifically around the human who must command them; in short, future aviation automation must be human-centered if it is to be a maximally effective tool. In automated aircraft, one essential information element is information concerning the status and activities of the automation itself. In many redundant aircraft systems, the human operator is informed only if there is a discrepancy between or among the units sufficient to disrupt or disable the performance of their functions.