Pilot Induced Oscillation
As a pilot-induced oscillation (PIO), including pilot Aircraft Coupling (PAC) in aviation is an undesirable behavior of the aircraft, which by an overreaction of the pilot on impact of its control pulses may occur. There is a risk of PIOs, especially if the control systems of the aircraft only react with a delay to the pilot's commands, which is why the pilot amplifies the control impulse and tries to counterbalance it with a strong reaction in the opposite direction after the aircraft reacts (which is now stronger than originally desired) . As a result, the aircraft oscillates around one of its axes, which can lead to critical situations.
Procedure and variants
The physics of an aircraft make this oscillation more difficult for pilots than for automobiles . Trying to make an aircraft climb by pulling the elevator automatically leads to a reduction in airspeed . Another factor is the speed of response of the instruments compared to the speed of response of the aircraft. Increasing the engine power will not cause an immediate increase in airspeed. In addition, the increase in the rate of climb is not immediately displayed on the variometer .
A pilot seeks z. Assume, for example, a sink rate of 500 feet per minute. However, if the aircraft sinks faster, he begins to counteract the descent by pulling the elevator until the variometer shows the desired rate of descent. Due to the delay of the variometer, however, the aircraft is already sinking at a lower rate of descent. By pressing the elevator, the pilot tries to compensate, which starts the process again. Stabilizing the rate of descent is more difficult than expected, as the rate of descent also changes the airspeed.
The most dangerous oscillation caused by a pilot can occur during landings . Pulling too hard on the elevator for a short time can cause the aircraft to slow down and there is a risk of stalling . A natural reaction in such a case is to push your nose down, which in turn leads to too much sinking. A subsequent pull repeats the process.
Examples
- In the Controlled Impact Demonstration aircraft crash test , the partial failure is also ascribed to PIO, as a result of which the machine hit significantly outside the tolerance values of the test.
- With hang-gliders, the aircraft reacts with a significant delay to control impulses from the pilot to the right and left. This can lead to unwanted rocking in right-left curves
- The last flight as part of the test for approach and landing attempts of the newly developed space shuttle Space Shuttle revealed a problem with the flight control system, which made it susceptible to this undesirable behavior.