Layh and Gebre-Egziabher Figure 12. Attitude solution during an actual GPS sensor failure. Figure 13. Ground track of UAV during a GPS sensor failure. Figure 12. By contrast, the fault-tolerant decentralized system provides a smooth position estimate that ignores the erroneous GPS measurements and tracks the good measurements after they converge back to the truth. Therefore, the safety of the aircraft would have been maintained, and the UAV could have completed multiple segments of fully autonomous waypoint navigation despite the faulty sensor measurements. SEPTEMBER 2017 CONCLUSION This article presented a filter design that allows the FCS of a small UAV to gracefully degrade from a loss of GNSS and gracefully recover upon subsequent restoration of GNSS services. The approach uses sensors already found on most current small UAV FCSs. When GNSS is denied, the covariance matrix of the parallel IEEE A&E SYSTEMS MAGAZINE 13