The hazard of spatial disorientation during helicopter flight using night vision devices

Night Vision Devices (NVDs) provide an enormous advantage to the operational effectiveness of military helicopter flying by permitting flight throughout the night. However, compared with daytime flight, many of the depth perception and orientational cues are severely degraded. These degraded cues predispose aviators to spatial disorientation (SD), which is a serious drawback of these devices.

As part of an overall analysis of Army helicopter accidents to assess the impact of SD on military flying, we scrutinized the class A-C mishap reports involving night-aided flight from 1987 to 1995. The accidents were classified according to the role of SD by three independent assessors, with the SD group further analyzed to determine associated factors and possible countermeasures.

Almost 43% of all SD-related accidents in this series occurred during flight using NVDs, whereas only 13% of non-SD accidents involved NVDs. An examination of the SD accident rates per 100,000 flying hours revealed a significant difference between the rate for day flying and the rate for flight using NVDs (mean rate for daytime flight = 1.66, mean rate for NVD flight = 9.00, p < 0.001). The most important factors associated with these accidents were related to equipment limitations, distraction from the task, and training or procedural inadequacies.

SD remains an important source of attrition of Army aircraft. The more than fivefold increase in risk associated with NVD flight is of serious concern. The associated factors and suggested countermeasures should be urgently addressed.