A Study on Software Bugs in Unmanned Aircraft Systems

Control firmware in unmanned aircraft systems (UAS) manage the subsystems for in-flight dynamics, navigation and aircraft sensors. Computer systems on-board the aircraft and on gateway machines can now support rich features in the control firmware, such as GPS-driven waypoint missions and autonomy. However, the source code behind control firmware can harbor software bugs whose symptoms are detectable only during flight. Often, software bugs in UAS have serious symptoms that lead to dangerous situations. We studied previously reported bugs in the open-source repositories of ArduPilot and PX4, two widely used control firmware for UAS, and characterized their root causes, severity and position in the firmware architecture. Even though both platforms have employed rigorous software engineering practices, bugs were common and often had severe symptoms (e.g., crashes.) In particular, bugs associated with mishandling aircraft sensor readings were the leading cause for bug-induced crashes. Finally, we used simulation to study the symptoms of sensor bugs and found that source code repositories under reported their frequency and impact. Our study motivates multiple research directions on software reliability in UAS firmware.