Perceived Pilot Workload and Perceived Safety of RNAV (GNSS) Approaches

Area navigation global navigation satellite system (RNAV (GNSS)) approaches have been used in Australia since 1998 and have now become a common non-precision approach. Since their inception, however, there has been minimal research of pilot performance during normal operations outside of the high capacity airline environment. Three thousand five hundred Australian pilots with an RNAV (GNSS) endorsement were mailed a questionnaire asking them to rate their perceived workload, situational awareness, chart interpretability, and safety on a number of different approach types.

Further questions asked pilots to outline the specific aspects of the RNAV (GNSS) approach that affected these assessments.

Responses were received from 748 pilots, and answers were analysed based on the aircraft performance category¹ . For pilots operating Category A and Category B aircraft (predominantly single and twin-engine propeller aircraft), the RNAV (GNSS) approach resulted in the highest perceived pilot workload (mental and perceptual workload, physical workload, and time pressure), more common losses of situational awareness, and the lowest perceived safety compared with all other approaches evaluated, apart from the NDB approach. For pilots operating Category C aircraft (predominantly high capacity jet airliners), the RNAV (GNSS) approach only presented higher perceived pilot workload and less perceived safety than the precision ILS approach and visual day approach but lower workload and higher safety than the other approaches evaluated. The different aircraft category responses were likely to have been due to high capacity aircraft having advanced automation capabilities and operating mostly in controlled airspace. The concern most respondents had regarding the design of RNAV (GNSS) approaches was that they did not use references for distance to the missed approach point on the approach chart and cockpit displays. Other problems raised were short and irregular segment distances and multiple minimum segment altitude steps, that the RNAV (GNSS) approach chart was the most difficult chart to interpret, and that five letter long waypoint names differing only by the last letter can easily be misread.

1. Aircraft performance approach categories are determined by multiplying the aircrafts stall speed in the approach configuration by a factor of 1.3. See Section 3.1.