Effects of three helmet-mounted display symbologies on unusual attitude recognition and recovery

Background: Helmet-mounted displays (HMDs) allow pilots to view aircraft instrument information while looking to the side, away from the aircraft centerline axis. In that situation, pilots may lose attitude awareness and thus develop spatial disorientation. A secondary concern is the possible effects of visual conflict between the apparent motion of traditional, nose-referenced flight symbology and the off-axis view of the outside world. Hypothesis: Alternative symbologies will provide improved attitude awareness for HMDs when compared with the conventional inside-out symbology now used with head-up displays (HUDs), if the HUD symbology is used on a HMD. Methods: The 9 pilots were presented 48 randomly arranged unusual attitude conditions on a HMD. The three symbologies included: 1) the inside-out representation now used with fixed HUDs, which features a moving horizon and pitch ladder; 2) an outside-in display that depicts a moving aircraft relative to a fixed horizon; and 3) an inside-out novel symbology termed the 'grapefruit' display (GD). The background scene contained a mix of either a front view orientation or a side view one. Conditions were randomized within and across subjects. Subjective preferences were collected after the completion of all tasks. Results: Analysis of variance repeated measures design revealed that stick input for the GD was significantly faster with fewer roll reversal errors than either of the other two. The time to recover to straight and level was significantly shorter for the front view orientation than the side view. Of the nine pilots, eight preferred the GD symbology as a method of presenting attitude information on the HMD. Conclusion: Results suggest the current HUD symbology is not the best way of displaying attitude information on the HMD. Given the conditions of this study, the best way of presenting the pilot with attitude information on the HMD is with the CID symbology.