Ghosts in the Sky: Creating Phantom Aircraft with Mode-S Transponder Spoofing

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Presented at BSides Bristol 2026 by

Alex Carr

Modern commercial aircraft constantly exchange information using Mode-S transponders, ADS-B broadcasts, and TCAS collision avoidance messages. These systems help keep aircraft safely separated, but were designed before authenticated wireless communications became a security concern. This talk provides an introduction to the protocols that underpin airborne collision avoidance and investigates whether a phantom aircraft could be introduced into the ACAS surveillance process through maliciously crafted Mode-S transmissions.