Real-Time Detection of Pilot-Induced Oscillations

Abstract

Despite decades of work to develop methods for their prevention, pilot-induced oscillations (PIOs) continue to occur. Reports of PIO on operational aircraft, including commercial airline transports, are increasing. This paper summarizes the challenges with attempting to detect PIO in real-time. It provides evidence to show that out-of-phase control/response activity between pilot and aircraft is common in closed-loop control, and therefore that there is no such thing as a “pre-PIO” condition that can be identified to prevent PIO. Since PIOs cannot be prevented, they will continue to occur, and methods are needed to mitigate the risk of catastrophic PIO. This paper discusses the challenges to detection of PIO in real-time. It describes the design of a method for the real-time detection of PIO that can be used to alert the flight crew in the early stage of a PIO, before the event has become catastrophic. With early warning, it is possible that loss of aircraft can be prevented through appropriate pilot response. The detection method is shown to have applications in flight test as well as operational use. The method is effective at identifying any oscillatory behavior in real-time, with applications for flight testing when sinewaves or frequency sweeps are applied to the test aircraft.