Preliminary Communication
and
This article belongs to the Special Issue No. 1, 2026 on Security 4.0 – Cybersecurity and Digital Resilience of Information Systems (CYRES 2026)
Ž. Jovanović, K. Kuk, and E. Mekić, “State-Machine Oscillations and Anomaly Detection in PX4 Offboard Mode Using Timed Automata Observers,” International Journal of Innovative Solutions in Engineering, no. S1, pp. 110–125, Oct. 2026, doi: 10.47960/3029-3200.2026.S1.110.
pages 110-125
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Abstract
Drones, as unmanned aerial vehicles (UAVs), operate through a predefined set of flight states. In this work, the PX4 autopilot is modeled as a state machine designed with drone safety as a primary consideration. Individual states and the corresponding transition conditions are defined to describe the behavior of the autopilot during flight. An experiment is conducted to investigate the influence of setpoint commands received from an external source on the PX4 state machine. Particular attention is given to scenarios in which oscillations between states occur, representing anomalous behavior that may lead to instability in drone operation. Communication is established among the PX4 autopilot, a ground control station (GCS), and a Python script executed on a computer within the same local network. The command format follows the MAVLink 2.0 communication protocol. The Python script provides external control of the UAV while operating in Offboard mode. The PX4 parameter COM_OF_LOSS_T specifies the timeout interval after which the autopilot triggers a failsafe action if a new setpoint message is not received within the defined period. The most significant behavior is observed when the delay between two consecutive setpoint messages is approximately 50 ms longer than the timeout specified by COM_OF_LOSS_T. Under these conditions, the UAV repeatedly transitions between its current operational state and the failsafe state, thereby producing oscillatory behavior in the PX4 state machine. The activated failsafe mechanism consequently forces the UAV to initiate a landing procedure.
Keywords
UAV, State Machine, Offboard Mode, COM_OF_LOSS_T, MAVLink
ijise ID
33
Publication Date
In Press
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