Definition

The Servo Transparency phenomenon, also known as Servo Reversibility or Jack Stall, can be encountered during abrupt manoeuvring of any single hydraulic system-equipped helicopter, particularly at high speeds. The phenomenon marks a flight envelope boundary.

This aircraft phenomenon occurs smoothly and is not dangerous if properly anticipated by a pilot during an abrupt or excessive high load manoeuvre such as a high positive g turn or pull-up. The factors that affect Servo Transparency are airspeed, collective pitch input, gross weight, "G" loads and density altitude.