Head-up displays. The integrity of flight information

Most single-pilot military aircraft are now being designed with head-up displays (HUD). The HUD has given the pilot a flight and weapon aiming display which has enhanced the safe operational flight envelope and the flexibility of weapons delivery. But has it benefited from the vigorous integrity analysis which has been given to other flight critical systems? The traditional pilot´s instrument panel has both main and standby instruments laid out in a prescribed pattern for efficient scanning. The pilot has responsibility for crossmonitoring between these totally independent systems and for making a judgment in the event of deviance. Pilot monitoring, albeit over a much larger scan area, was also assumed when HUDs were introduced into the cockpit. This resulted in significant increases in physiological and psychological workload. This first generation of HUDs earned themselves a reputation for poor reliability and for a high occurrence of erroneous, but plausible, displays. This unsatisfactory performance has frustrated attempts to classify the HUD as the primary flight display and has forced responsibility for display monitoring onto the pilot. To improve this situation, the equipment manufacturers have made vigorous attempts to improve unit reliability and to extend the scope of their self-monitoring circuits. Is this the right approach? The paper is not directly concerned with reliability of these equipments but in examining how to ensure that specific flight critical data is always correctly displayed and that all failure conditions are `infallibly¿ signalled to the pilot. The solutions to this problem can range from a reorganisation of the cockpit, thus reducing pilot workload to a level where cross monitoring is always possible, to the addition of redundant sensor and display systems with automatic crossmonitoring.