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Flight instrument interpretability has been a key piloting issue because it is directly related to operator performance and inversely related to operator error. To improve interpretability we have developed the Sky Arc, a new symbology initially developed for attitude control, particularly for a helmet-mounted display. It consists of an integrated set of graphic symbols which vary in a continuous, analog fashion with changing flight parameters. The Sky Arc currently integrates, pitch, roll, heading, air speed, and terrain avoidance. The display can be integrated into a head down display, a head up display, or a helmet mounted display. In this preliminary study the usability of the Sky Arc as an attitude indicator was compared to a conventional head-up display pitch ladder symbology. The test involved six test subject pilots and a medium-fidelity simulator. The pilots were asked to fully recover from a series of unusual attitude conditions that were presented on the simulator. The time taken to recover and the correctness of the recovery procedure served as the objective evaluation measures. A Likert-type rating scale and open-ended subject matter expert opinions served as the subjective measures of evaluation. To examine whether there was a relationship between usability of the attitude indicator and difficulty of the unusual attitude, the workload levels involved in performing the unusual attitude recoveries were grouped into three levels, low, medium, and high. At each workload level there were four conditions, for a total of 12 different conditions. Each pilot was asked to recovery twice from each condition, for a total of 24 unusual attitude recovery trials. The test trials were counterbalanced and displayed in a prearranged order. No differences due to difficulty of the unusual attitude were detected. Overall, the study revealed that the Sky Arc led to generally faster recoveries than did the standard display, as well as higher subjective preference ratings. Although the pilots had thousands of hours of familiarity with pitch ladder symbologies, they recovered more quickly using the Sky Arc symbology with which they had had no previous experience. This evidence suggests that further research is warranted to examine the utility of the Sky Arc symbology.
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