Deborah L. Bakowski

A methodical approach for developing valid human performance models of flight deck operations

Validation is critically important when human performance models are used to predict the effect of future system designs on human performance. A model of flight deck operations was validated using a rigorous, iterative, model validation process. The process included the validation of model inputs (task trace and model input parameters), process models (workload, perception, and visual attention) and model outputs of human performance measures (including workload and visual attention). This model will be used to evaluate proposed changes to flight deck technologies and pilot procedures in the NextGen Closely Spaced Parallel Operations concept.

Flight Deck Surface Trajectory-Based Operations

The results of three piloted simulations investigating flight-deck surface trajectory-based operations (STBO) are presented. Commercial transport pilots were given taxi clearances with time and speed components on the primary flight display and were required to taxi to the departing runway or intermediate intersections. Results show that when pilots were provided with speed-only taxi clearances, pilots either had poor required time of arrival (RTA) conformance with acceptable estimates of attentional distribution and safety, or had good RTA conformance with unacceptable attentional distribution and safety estimates. A flight-deck error-nulling algorithm/display allowed pilots to conform accurately with taxi RTA clearances while maintaining safety. Results are discussed in terms of pilot multitasking in the busy airport surface operations environment.

NextGen Surface Trajectory-Based Operations: Contingency-hold clearances

The purpose of this pilot-in-the-loop taxi simulation was to investigate a NextGen Surface Trajectory-Based Operations (STBO) concept called “contingency holds.” The contingency-hold concept parses a taxi route into segments, allowing an air traffic control (ATC) surface traffic management (STM) system to hold an aircraft when necessary for safety. Under nominal conditions, if the intersection or active runway crossing is clear, the hold is removed, allowing the aircraft to continue taxiing without slowing, thus improving taxi efficiency, while minimizing the excessive brake use, fuel burn, and emissions associated with stop-and-go taxi. However, when a potential traffic conflict exists, the hold remains in place as a fail-safe mechanism. In this departure operations simulation, the taxi clearance included a required time of arrival (RTA) to a specified intersection. The flight deck was equipped with speed-guidance avionics to aid the pilot in safely meeting the RTA. On two trials, the contingency hold was not released, and pilots were required to stop. On two trials the contingency hold was released 15 sec prior to the RTA, and on two trials the contingency hold was released 30 sec prior to the RTA. When the hold remained in place, all pilots complied with the hold. Results also showed that when the hold was released at 15-sec or 30-sec prior to the RTA, the 30-sec release allowed pilots to maintain nominal taxi speed, thus supporting continuous traffic flow; whereas, the 15-sec release did not. The contingency-hold concept, with at least a 30-sec release, allows pilots to improve taxiing efficiency by reducing braking, slowing, and stopping, but still maintains safety in that no pilots “busted” the clearance holds. Overall, the evidence suggests that the contingency-hold concept is a viable concept for optimizing efficiency while maintaining safety.

Flight deck surface trajectory-based operations (STBO): A four-dimensional trajectory (4DT) simulation

In four-dimensional trajectory (4DT) Surface Trajectory-Based Operations (STBO), aircraft are assigned a conflict-free 4DT which defines an expected location (x, y coordinates) at all times, t, along the taxi route (with altitude, being fixed). These 4DTs afford the highest temporal certainty at all points along the taxi route, and at the departure runway. In the present study, a 4DT flight deck display was presented on the Airport Moving Map (AMM) to support pilot conformance to a 4DT clearance while taxiing under manual control. This pilot-in-the-loop simulation compared the effect of 4DT flight deck display formats on distance from the expected 4DT location, conformance to the displayed tolerance band, eyes-out time, and pilot ratings of safety and workload. In the defined-tolerance display format, a graphical representation of the expected 4DT location, with a distance-based allowable-tolerance band, was depicted on the AMM. Two defined-tolerance band sizes were tested +/−164 ft and +/−405 ft. In the undefined-tolerance display format, the expected 4DT location was displayed graphically on the AMM, with no indicated allowable-tolerance bounds. Each taxi trial included 4DT speed changes (two or five, per trial) and a range of 4DT taxi speeds. Results showed that the larger (+/−405 ft) defined-tolerance band yielded higher conformance levels than the smaller (+/−164 ft) band, with pilots staying within the specified and displayed conformance bounds more in the larger (99.71%) than the smaller defined-tolerance band (93.37%). However, in terms of being able to predict the location of the aircraft compared to the expected 4DT location, the smaller defined-tolerance band resulted in pilots keeping their aircraft closer to the 4DT location, for both average distance and for a given confidence interval (e.g., 95%), than either the larger defined-tolerance band or the undefined-tolerance display format. The larger tolerance band yielded more “eyes out-the-window” time than the smaller tolerance band. Pilots also rated taxing with the larger tolerance band as safer than the smaller tolerance band.