Abstract
Five different head-up display (HUD) airspeed and altitude symbol sets were examined for efficacy in a basic instrument crosscheck during visually simulated flight. Twenty-five pilot subjects used each HUD symbol set while tasked to maintain straight and level flight for 200 seconds. Airspeed and altitude were caused to vary during the flight profile, requiring the pilots to recognize deviations and correct back to target conditions. Root mean square (RMS) performance errors (deviations from assigned airspeed and altitude) were measured. The pilots' airspeed and altitude performance was significantly better (p<0.01) with two new formats — rotating pointers with dot scales and plain rotating pointers—than with two more common formats—boxed digits and moving vertical tapes. Another novel format, boxed digits with trend bars, provided the best performance with respect to altitude error, but not airspeed error. Measures of subjects' confidence in their ability to use the different displays for basic instrument flight were significantly different (p<0.001) and consistent with the performance measures. The results of this study are important because of the need to standardize HUD symbology, and because of the trend to make the HUD, rather than the panel instruments, serve as the single-source primary flight reference in military aircraft.
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