Assessment of Helmet Mounted HUD Symbology Referencing Systems

The TTCP Technical Panel2 TP2 developed a HUD symbology set using a mixed referencing system in which symbols portraying spatial analogue information are aircraft or world referenced, whereas non-spatial symbols are head referenced. One potential advantage to having non-spatial symbols referenced to head position is that critical flight and power information can be made available to the pilot even when the pilots gaze is directed to the side of the aircraft, such as during sidestep maneuvers. It is not clear, however, whether pilots can effectively use a mixed referencing system. For example, one potential problem is that depending on moment-to-moment positioning of the head, one or more of the head referenced symbols may overlap with the aircraft referenced symbols. This may create intolerable perceptualcognitive confusion and high mental workload. There were two objectives of the present research. The first objective was to contrast the effectiveness of the TP2 mixed frames of reference against an aircraft and a fully head-referenced configuration. To do this, two ADS33-type tasks were used formation flight and sidestep. The formation flight results showed that there was undifferentiated performance across the aircraft, mixed, and head FORs. The sidestep results showed an advantage for the mixed and head FORs over the aircraft FOR in two primary performance measures maintaining heading and altitude. The superiority of the mixed and head FORs for the sidestep maneuver was also reflected in the pilots ratings. A second objective of the present research was to take a step toward establishing a paradigm to assess the effects of space-based and object-based attention in processing of HUD symbology. To do this, pilots ability to discriminate targets that appeared on a HUD was assessed across the mixed, aircraft and head-referenced configurations.