Potential operational consequences of the use of ACAS Xu in controlled airspace

Abstract

A “detect-and-avoid” capability providing a” remain well-clear” function will be needed for unmanned aircraft to fly safely in uncontrolled airspace but could also be used in controlled airspace, provided that the action chosen by the pilot, based on the system suggestive guidance, is compatible with the current air traffic control clearance or an amended clearance. The study reported in this paper looked at the potential operational consequences of the interaction between the pilot and the controller in controlled airspace when a clearance amendment must be requested by the pilot, using the recently standardized detect-and-avoid system, ACAS Xu. Simulations on a selected encounter in Japanese airspace were performed, first with only the unmanned aircraft equipped with ACAS Xu and the other aircraft equipped with current collision avoidance system, then with both aircraft equipped with ACAS Xu. A model of pilot behavior when faced with a remain-well-clear alert (including pilot-controller communication delays) was used. The analysis of the qualitative results outlined three areas of concern: the possible confusion caused by multiple changes of remain-well-clear guidance, the undesirable effects when both aircraft are equipped with ACAS Xu and the potential interaction with short term conflict alerts displayed on the controller working position.