Final answer:
The rudder PEDAL DISC button on a steering hand wheel of an aircraft is used to disconnect the rudder pedals from the nose wheel's steering mechanism during ground operations, preventing unintended steering inputs. This feature enhances safety and control while the aircraft is taxiing. Once airborne or when full control is necessary, the button is released to allow rudder input.
Step-by-step explanation:
The rudder PEDAL DISC button on the steering hand wheel is a feature found in some aircraft, particularly jetliners. When the button is pressed, it typically disengages or 'disconnects' the rudder pedals from the steering mechanism of the nose wheel. This is a safety feature that prevents unwanted input from the rudder pedals while the aircraft is being steered on the ground by the tiller on the steering hand wheel, which is usually operated by the pilot during taxiing. When the aircraft is ready to take off and the pilot needs full control over all steering aspects, including the rudder, the PEDAL DISC button is released, thus reconnecting the rudder pedals.
In practice, this means that the pilot can prevent any inadvertent or unintentional rudder pedal movements from affecting the direction the plane is moving on the ground. A scenario in which this might be beneficial is when there is another crew member in the cockpit who might accidentally touch the rudder pedals, or when there are mechanical issues with the pedal linkage that need to be isolated to maintain control of the aircraft during ground maneuvers. Once the aircraft reaches a phase where rudder pedal input is needed again, such as during takeoff and landing, the pilot can engage the rudder pedals to ensure full control over the aircraft's movements.