4-D Taxi Clearances: Pilots' Usage of Time- and Speed-Based Formats

Automated surface management systems are being developed that utilize dynamic algorithms to calculate the most efficient movement of all surface traffic in order to increase the efficiency with which airport surfaces are utilized. If these systems are to be implemented, pilots will be required to comply with 4-D taxi clearances, in which a pilot is required to be at a specific location at a specific time. This pilot-in-the-loop simulation study is an investigation of how to present the information necessary for pilots to comply with such 4-D taxi clearances. This study is aimed at determining the fundamental abilities that pilots have in complying with clearances given as time-based versus speed-based commands, without the use of an advanced display. Using a medium-fidelity surface operations simulator at NASA Ames Research Center, with Boeing 737 modeled dynamics, 18 commercial airline Captains each completed 45 taxi clearance scenarios. Each taxi clearance scenario required pilots to follow a cleared taxi route and to make an active runway crossing at a specific future time by following either a time-based or speed-based clearance. Taxi clearances were presented using: 1) a Speed format that displayed current ground speed and a commanded average ground speed; 2) a Time format that displayed elapsed time and a commanded time of arrival; or, 3) a Speed/time format that displayed all of the information from the Speed and Time formats simultaneously. Pilots’ time-of-arrival (TOA) absolute error, TOA error bias, and velocity standard deviation (SD) were recorded for each trial. Overall, the results suggest that having both speed and time information provides more accurate and less variable 4-D clearance compliance. Additionally, the results indicate that utilizing shorter taxi clearances can maximize TOA accuracy. This baseline study indicates that the development of flight deck displays for 4-D taxi clearances may likely require the presentation of both time-based information and speed-based information for accurate and efficient use by the flight crew.