Analysis of Chinook AFCS induced divergent pitch oscillations with reference to an Australian army accident

Abstract

In 2011 an Australian Army CH-47D Chinook was involved in an accident in which a series of uncommanded pitch oscillations were experienced, resulting in one fatality and the loss of the aircraft. The accident was followed by three similar incidents. The Flight Data Recorder was not recovered for the accident but was recovered for the incidents, and this data was used to investigate a possible cause of the oscillations which occurred in the lead up to the accident. Simulations were undertaken to demonstrate that the likely cause of the oscillations was limit saturation of the Advanced Flight Control System. Recovery procedures were developed to help prevent future occurrences, and handling qualities for recovery were assessed. This accident highlighted the importance of testing aircraft systems to their limits and the importance to operators of understanding the implications of these limits.