What is the purpose of the by pass pin in aircraft ground handling?

The bypass pin is an important tool used in aircraft ground handling, particularly for safely preparing the aircraft for towing. Its primary purpose is to signal that the aircraft is ready to be towed by indicating that the aircraft's brake system is in a disengaged state. When the bypass pin is inserted, it allows ground personnel to maneuver the aircraft safely on the ground without the risk of the brakes engaging unexpectedly.

This mechanism ensures that all safety protocols are followed during the towing process. By confirming the state of the aircraft's systems, personnel can proceed with towing operations with confidence that the aircraft will not move independently and will respond as expected when being towed.

In contrast, the other options do not accurately reflect the function of the bypass pin. Fueling does not rely on the bypass pin, securing doors is a separate safety procedure, and engine start prevention is managed through other operational protocols, not by the presence of a bypass pin.