Also found in: Acronyms.
Mode S[′mōd ′es]
An augmentation of the Air Traffic Control Radar Beacon System in which each aircraft is equipped with a transponder that replies when interrogated with a discrete identity code. Also known as ADSEL (in Britain); discrete address beacon system or DABS (in the United States).
Mode S stands for mode select. Mode S transponders are used in conjunction with a traffic alert and collision avoidance system. This mode permits the exchange of digitally encoded information between the ground controller and individual aircraft.