A Steering Bypass Pin is required to give the ground crew control of the nose wheel to enable them to move the aircraft.  This pin is required to give the ground crew control of the nose wheel to enable them to move the aircraft.

The Boeing series of aircraft require different size pins for different aircraft.

For use towing and on pushback of aircraft.  Many aircraft require the use of a Steering Bypass Pin.  The pin is located in the steering lock out mechanism.  This is done before the attachment of all equipment used for the pushback and movement of an aircraft .  This bypasses the hydraulic steering of the nose wheel giving control of the aircraft steering to the ground crew.

Failure to use the correct pin will result in damage to the nose gear of the aircraft and towing equipment.   It could also endanger the ground crew working on the aircraft.
Failure to remove the pin from the aircraft will result in the pilot being unable to steer the aircraft from the flight deck.  To help prevent this happening any steering pin being used on an aircraft must fitted with a Remove Before Flight flag to clearly show that the pin is located inn the aircraft.