Recent experience in flight testing for pilot induced oscillations (PIO) on transport aircraft

Though the subject of pilot induced oscillations (PIO) is not new, it has g arnered significant attention in the past several years. Since the mid-1990 s, Boeing Commercial Airplanes has been conducting specific flight tests of its products in order to evaluate PIO tendencies. Beginning with the 777-2 00, a generic suite of test manoeuvres has been used to evaluate PIO tenden cies on each product. The testing has been conducted on a 'window of opport unity' basis with the intent to gather data and evaluate each model. To dat e, specific evaluations have been carried out on six different aircraft mod els spanning a wide range of aircraft sizes, inertial characteristics, and control system implementations. Each manoeuvre in the generic suite is disc ussed in detail. In addition, along the way, a large number of other manoeu vres have been used at various times to evaluate PIO tendencies. These are briefly described. No single test manoeuvre or technique has been identifie d which provides effective discrimination of PIO tendencies. Finally, the s ubject of the pilot in the loop is discussed with regard to achieving consi stency in conducting PIO evaluations.