Servo transparency

In aviation, and in particular in helicopters, servo transparency (also called servo reversibility or jack stall), is a phenomenon affecting the servomechanisms (or servos) that assist a helicopter's flight controls, which, in certain flight conditions, can result in a significant stiffening of the controls handled by the pilot. The effect, if not promptly recognised by the pilot, can be hazardous as it can lead to partial or total loss of control, which, if encountered at low altitude, could result in impact with terrain.^: 101