Pilot Performance, Workload, and Situation Awareness During Lunar Landing Mode Transitions

Aircraft and spacecraft pilots frequently change their level of supervisory control between full autopilot and other modes, providing varying levels of manual control. Therefore, multimodal systems must transition "gracefully," meaning without unsafe decreases in flight performance or unacceptable changes in workload or situation awareness. Thirteen subjects flew a fixed base simulation of the NASA Constellation Program Altair lunar lander that transitioned from full autopilot to one of three flight-director-guided rate-command attitude hold manual control modes. After training, each subject flew 24 approaches, half of which included a landing point redesignation at the time of the mode transition requiring the pilot to null additional guidance errors. Bedford subjective workload and two-choice embedded secondary task response times were used to quantify temporal changes in mental workload. Situation awareness transients were detected by analysis of a tertiary task, verbal callouts of altitude, fuel, and terrain hazards. Graceful transitions were particularly difficult because Altair's large inertia made the plant dynamics relatively sluggish. Transitions to manual control increased subjective and objective workloads and decreased callout accuracy in proportion to the number of flight control axes being manually commanded.