When gauges fail and clouds are tall,we miss the horizon most of all: General Aviation pilot responses to the loss of attitude information in IMC

Abstract

Sixty pilots were exposed to a vacuum-system failure during a flight simulation, 48 in a Piper Malibu simulator and 12 in a simulated Cessna 172. Instrumentation failure was varied for the five display configurations such that 12 pilots (1) lost head-down heading and attitude indicator (AI), (2) lost only the primary AI (horizontal situation indicator, HSI, was electric), (3) lost the primary AI but had the HSI plus a back-up electric AI, (4) lost the AI and directional gyro (DG), or (5) lost the AI but had an HSI (only in the Cessna 172 simulator). Primary panel (loss of AI and DG) showed the highest loss rate (83%). The proposed back-up AI in place of turn coordinator produced a 33% loss rate. Standard Malibu instrumentation (HSI) produced a 25% loss rate. Having all options (HSI, TC, back-up AI) reduced loss rate to just 8%. Data suggest that the presence of a back-up attitude indicator can ameliorate the rate of loss of control, but that the presence of the HSI had a similar effect. Combining the two produced the best outcomes. Results are discussed in relation to potential interventions, including attitude and heading indicators and annunciators for system failure.