American Institute of Aeronautics and Astronautics
Recommended Practices for Exposing Pilot-Induced
Oscillations or Tendencies in the Development Process
David G. Mitchell
Hoh Aeronautics, Inc., Lomita, CA, 90717
David H. Klyde
Systems Technology, Inc., Hawthorne, CA, 90250
It has now been more than a century since the first powered flight took place on the
dunes of Kill Devil Hills.
An often overlooked element of those remarkable first four flights
was the occurrence of longitudinal axis pilot-induced oscillations (PIO).
Looking back it is
now easy to see how the inherent instability of the 1903 Wright Flyer design resulted in PIO
with either Orville or Wilbur at the controls.
Since that time, aircraft have grown in
capability and complexity.
For example, the systems designed to control the aircraft have
evolved from reversible cables and pulleys where the force of the pilot’s inputs directly
manipulates the control surfaces to modern fly-by-wire designs where software
interpretations of the pilot’s inputs manipulate the control surfaces.
There has been,
however, one constant through this evolution – the ongoing occurrence of pilot-induced
oscillations, sometimes with catastrophic results. In the last 30 years almost every military
or commercial aircraft designed has experienced PIO, either in the development process or
in operational flight.
If recent history is any indication, PIO will certainly continue to occur
in the future.
In this paper, status of relevant PIO criteria will be given, on-board detection
and alleviation schemes will be described, and flight test methods will be reviewed.
recommended practices will be outlined to expose PIO tendencies, if they exist, so that the
catastrophic events can be minimized or eliminated.
ilot-induced oscillations have presented a challenge for aircraft designers to predict and eliminate since the first
powered flight of the Wright Brothers over a century ago. A list of some of the aircraft that have experienced
PIO, either in the development process, experimental flight test, or operational flight are listed in Table 1.
PIO has been a problem to solve on nearly every type of aircraft from the propeller age to the modern era.
Almost like clockwork PIO becomes an important problem to solve every 10 to 15 years, usually in association
with at least one highly visible event.
The first major push to comprehend and eliminate PIO came in the early
At this time at least three major PIO events were at the forefront of the research effort: 1) the X-15 Flight 1-
1-5 landing PIO, 2) the T-38A, and 3) the F-4 Sageburner high speed, low altitude record run.
The X-15 event
occurred during the first unpowered glide of the X-15. The flight took place on June 8, 1959 with test pilot Scott
Crossfield at the controls.
The aircraft was flown with the pitch damper off using the side located controller.