Helicopter Pilot Performance: Inadvertent Flight into Instrument Meteorological Conditions

Abstract

The problem of inadvertent VFR flight into IMC has been well documented as a major cause of general aviation accidents. The performance limits of fixed wing pilots under these circumstances have also been investigated with alarming results. However this problem has not yet been studied sufficiently in civilian helicopter pilots. In general helicopter operations are more complex than those of fixed wing aircraft for several reasons including increased control difficulty and the ability to operate in a variety of flight regimes such as slow flight, hover, low level, and high speeds. Each of the different helicopter flight regimes has different operational and control demands. The present study is aimed at quantifying helicopter pilot performance after inadvertent VFR into IMC at different speeds and altitudes of operation. We report here on data collected from instrument rated commercial helicopter pilots in simulated flight from VFR conditions to IMC. Data were collected on the aircraft attitude and performance as well as pilot control inputs. In addition an objective analysis was performed on the pilot input data that provided information regarding the amount of corrections that the pilots were using during flight. This analysis treated pilot inputs as a time series and quantified variability in the control inputs by calculating power in the Fourier spectrum of the digitized control position data stream. This analysis is valuable in that it provides an objective measure of pilot effort. The analysis was also applied to aircraft performance metrics. An “error” analysis was also conducted on the aircraft attitude data which enumerated the rate at which the aircraft was judged to be in a attitude that would reduce safety as predetermined by helicopter pilot experts. Both analyses revealed important information regarding the relationships between visibility, altitude, airspeed, aircraft performance, and pilot effort. In particular, while pilots quickly improved performance such that safe attitudes were maintained, the amount of effort required to maintain proper attitude remained high for longer periods of time. Pilot effort eventually decreases with repeated practice.