Aircraft Inertial Measurement Unit Fault Diagnosis Based on Optimal Two-Stage UKF Qizhi He, Weiguo Zhang, Degang Huang, Huakun Chen and Jinglong Liu JNWPU, 36 5 (2018) 933-941 Published online: 17 December 2018 DOI: 10.1051/jnwpu/20183650933