Accidental Systems, Hidden Assumptions and Safety Assurance

In April, the Royal Academy of Engineering published the final report of a study into the world’s increasing dependence on GPS and other global navigation satellite systems and the consequent vulnerabilities. The report, Global Navigation Space Systems, describes how GPS has been so useful and so reliable that a remarkably wide range of applications, ranging from financial trading to deep sea drilling, now depend on these extremely weak signals from space. As a consequence, if the GPS signals are disrupted or spoofed, many services that might be thought to be independent may fail simultaneously. Primary and backup systems may both be affected. In this paper, we explain some of the vulnerabilities in GPS and other GNSS and draw some conclusions about accidental systems, hidden assumptions and safety assurance.