Pilot Control Behavior in Paired Approaches

A piloted flight simulator study investigated pilot control behavior while self-separating from a proximate aircraft during an instrument landing system approach. This “paired approach” operational concept pairs two aircraft, with the trail aircraft of the pair remaining within a safe zone calculated to be free (for a specified period of time) from collision danger and wake turbulence interactions. Enabling this operation would reduce dependent spacing between aircraft landing on closely spaced parallel runways in poor weather conditions, which is a significant source of weather-related delays. Pilots in the study flew the trail aircraft and were given displays that either showed the current safe zone, a “worst-case” safe zone based on information contained in the approach procedure, or both. The lead aircraft’s compliance to the expected procedure was also varied so that it either complied fully, changed its speed unexpectedly, or blundered across the trail aircraft’s flight path. It was anticipated that the pilots would track the safe zone, resulting in significantly different behavior depending on the type(s) of safe zone displayed to them. However, the results suggest a strategy of matching speeds with the lead aircraft, rather than tracking the safe zone. Since the procedures and technologies for paired approaches had not considered this strategy, changes to support pilots in using this strategy, or training to overcome it, are necessary.