What locking methods can be used to secure aircraft?

The methods used to secure aircraft are critical for ensuring safety and preventing unauthorized access. Among these methods, door locks and wheel locks play a vital role. Door locks are essential as they prevent unauthorized entry into the aircraft, protecting the interior and its contents. Wheel locks are utilized to deter movement of the aircraft on the ground, ensuring that it remains stationary and is secure from theft or accidental movement.

In contrast, the other methods listed do not effectively secure an aircraft. Key locks, while they may provide some security, are insufficient on their own because they do not address the potential vulnerabilities at points of access like doors and wheels. Flight plan amendments relate to navigation and flight operations rather than physical security measures. Hanging a sign, while it may serve as a notification or warning, does not provide any physical barrier to unauthorized access or movement of the aircraft. Therefore, the combination of door locks and wheel locks is the most comprehensive approach to ensuring that an aircraft is properly secured.