CDI Sensitivity and Crosstrack Error on Nonprecision Approaches

This report is concerned with the influence of display needle sensitivity on the accuracy with which pilots can fly nonprecision approaches. Twelve private pilots flew an instrumented single engine airplane on 144 approaches at six different sensitivity levels. The study was conducted to determine the influence of course deviation indicator CDI sensitivity on pilot tracking error. The sensitivities ranged from 15,190 feet 2.5 nautical miles to 475 feet 0.08 nautical miles for a full-scale deflection. Increase in sensitivity of this magnitude decreased crosstrack Root Mean Square error from an average of 0.22 to 0.04 nautical miles. Magnitude of the error influence of sensitivity on that increases in sensitivity on that magnitude were affected by distance from the missed approach point. Pilots reported that increases in sensitivity increased their-workload and changed their distribution of attention among the aircraft instruments used for navigation and directional control.