  We study an in-flight actuator failure recovery problem for a hexrotor UAV.
The hexrotor may experience external disturbances and modeling error, which are
accounted for in the control design and distinguished from an actuator failure.
A failure of any one actuator occurs during flight and must be identified
quickly and accurately. This is achieved through the use of a multiple-model,
multiple extended high-gain observer (EHGO) based output feedback control
strategy. The family of EHGOs are responsible for estimating states,
disturbances, and are used to select the appropriate model based on the system
dynamics after a failure has occurred. The proposed method is theoretically
analyzed and validated through simulations and experiments.
