Pilot Induced Oscillation

As a pilot induced oscillation ( PIO), also pilot Aircraft Coupling (PAC ) is an unwanted behavior of the aircraft, which can be caused by an overreaction of the pilot on impact of its control pulses in aviation. In particular, if the control systems of the aircraft only react with delay to the commands of the pilot, this therefore increases the control pulse and after reaction of the aircraft (which is now more pronounced than originally desired) with a strong reaction in the opposite direction to compensate tries, there is a danger of PIOs. As a result, the aircraft carries out a vibration about an axis thereof, which may lead to critical situations.

Sequence and variants

Physics of an aircraft makes this oscillation for pilots difficult than with motor vehicles. So automatically leads the effort to leave an aircraft climb by pulling back on the elevator, to a reduction in airspeed. Another factor is the rate of reaction of the instruments in comparison with the response speed of the aircraft. Increasing the engine power will cause no immediate increase in airspeed. In addition, the increase in the rate of climb is not immediately displayed on the variometer.

A pilot aiming eg at a sink rate of 500 feet per minute. However, decreases the aircraft faster, he begins to counteract the sinking by pulling back on the elevator until the variometer indicates the desired rate of descent. Due to the delay of the variometer, however, the aircraft descends already at a lower rate of descent. Pressing the elevator, the pilot attempts to compensate, so the process begins again. The stabilizing the rate of descent is more difficult than expected, since in addition also changes the airspeed with the rate of descent.

The most dangerous pilot induced oscillation can occur during landings. A short excessive pulling on the elevator can cause the aircraft is too slow and there is a danger of a stall. A natural reaction in such a case is to push the nose down, but this in turn leads to an excessive sink rate. A subsequent drawing repeats the process.

Examples

  • Pilot Induced Oscillation in 1992 was to blame for the plane crash of a prototype of F/A-22 Raptor during a landing at Edwards Air Force Base in California.
  • In February 1989 a prototype of the Saab JAS -39 Gripen crashed when landing in Linköping (Sweden). Here was PIO, triggered by a too sensitive and slow -reacting control system, the cause. As a result, the control system has been redesigned.
  • When plane - crash test Controlled Impact Demonstration partial failure is also attributed to PIO, as a result, the machine hit significantly out of tolerance values ​​of the experiment.
  • For hang-gliders the aircraft reacts with a significant delay on control signals from the pilot to the right and left. This can lead to an unwanted swaying in left-right curves
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