On a Collision Course: Unveiling Wireless Attacks to the Aircraft Traffic Collision Avoidance System (TCAS)

Collision avoidance systems have been a safety net of last resort in aviation since their introduction in the 1980s. Through constantly refined safety procedures and hard lessons learned from mid-air collisions, the Traffic Collision Avoidance System (TCAS) II Version 7.1 has become the global standard, significantly improving safety in a fast-growing field. Despite this safety record, TCAS was not designed with security in mind, even in its newest versions. With the rise of software-defined radios, security researchers have shown many wireless technologies in aviation and critical infrastructures to be insecure against radio frequency (RF) attacks. However, while similar attacks have been postulated for TCAS with its built-in distance measurement, all attempts to execute them have failed so far. In this paper, we introduce the first working RF attacks on TCAS. We demonstrate how to take full control over the collision avoidance displays and create so-called Resolution Advisories (RAs) of arbitrary aircraft on a collision course. We build the necessary tooling using commercial off-theshelf hardware, creating sufficient conditions for the attacker to spoof colliding aircraft from a distance of up to 4.2 km. We evaluate this and further attacks extensively on a live, real-world, certified aircraft test system and discuss potential countermeasures and mitigations that should be considered by aircraft and system manufacturers in the future.