Experimental study of helmet-mounted display symbology for terrain avoidance during low-level maneuvers

A simulation study was performed to evaluate Helmet-Mounted Display (HMD) symbology for fighter aircraft Ground Collision Avoidance Systems (GCAS). Several candidate visual alert symbologies were tested, including an iconic cue, an aircraft-fixed guidance cue, a head-fixed guidance cue, and a head-fixed guidance cue with a pitch ladder. Subjects were given audio and visual side-tasks and responded to alerts in different aircraft attitudes. Shorter reaction times were observed when a head-fixed visual alert was given in addition to the standard audio alert. No significant differences in recovery performance (measured by response time and altitude loss) were observed between display formats. However, the display format had a significant effect on subject head motion. With head-fixed guidance cues, pilots were able to perform the recovery maneuver with their heads off axis; with aircraft-fixed or no guidance cues, pilots consistently turned their heads to face forward before maneuvering the aircraft.