Simulator-induced spatial disorientation: effects of age, sleep deprivation, and type of conflict.

INTRODUCTION: Spatial disorientation mishaps are greater at night and with greater time on task, and sleep deprivation is known to decrease cognitive and overall flight performance. However, the ability to perceive and to be influenced by physiologically appropriate simulated SD conflicts has not previously been studied in an automated simulator flight profile. METHODS: A set of 10 flight profiles were flown by 10 U.S. Air Force (USAF) pilots over a period of 28 h in a specially designed flight simulator for spatial disorientation research and training. Of the 10 flights, 4 had a total of 7 spatial disorientation (SD) conflicts inserted into each of them, 5 simulating motion illusions and 2 involving visual illusions. The percentage of conflict reports was measured along with the effects of four conflicts on flight performance. RESULTS: The results showed that, with one exception, all motion conflicts were reported over 60% of the time, whereas the two visual illusions were reported on average only 25% of the time, although they both significantly affected flight performance. Pilots older than 35 yr of age were more likely to report conflicts than were those under 30 yr of age (63% vs. 38%), whereas fatigue had little effect overall on either recognized or unrecognized SD. DISCUSSION: The overall effects of these conflicts on perception and performance were generally not altered by sleep deprivation, despite clear indications of fatigue in our pilots.

Fatigue and related human factors in the near crash of a large military aircraft.

INTRODUCTION: During approach to a remote island location, a U.S. Air Force heavy-airlift aircraft was flown into an aerodynamic stall, resulting in the loss of more than 4000 ft of altitude, with the crew recovering the aircraft just before impact would have occurred. METHODS: An analysis of the mishap was conducted through a review of non-privileged USAF mishap data, cockpit voice recordings, flight data records, and interviews of the aircrew involved. A thorough examination of fatigue-related factors was conducted, including computerized fatigue modeling. RESULTS: The crew traveled over 11,000 mi in a westward direction over a 6-d period. They had been on duty for nearly 21 h on the day of the mishap, with minimal in-flight rest. The pilots were late beginning their descent for landing, and a minor aircraft malfunction distracted the crew, contributing to channelized attention and degraded situational awareness. A breakdown in crew communication and failure to adequately monitor and interpret true aircraft state culminated in loss of aircraft control. Analysis of the crew's work/rest schedule confirmed that multiple elements of fatigue were present during this mishap, including acute and cumulative fatigue, circadian disruptions, and sleep inertia. Additionally, reduced situational awareness and spatial disorientation, exacerbated by the underlying fatigue, were causal in this mishap. DISCUSSION: This mishap highlights the importance of maintaining a high degree of situational awareness during long-haul flights with a continuing need to address issues regarding spatial disorientation, proper application of human engineering principles in modern cockpits, and mitigation of aircrew fatigue factors.

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 GD symbology.