What is an acceptable method for securing unattended aircraft?

Securing unattended aircraft is crucial for ensuring safety and preventing unauthorized access. One of the most effective methods is to ensure that all aircraft doors and compartments are closed and latched. This practice limits access to the aircraft, protecting both the internal systems and any cargo or valuables that may be inside. Properly latching doors and compartments not only minimizes the risk of theft but also prevents unauthorized individuals from tampering with the aircraft's systems, which is vital for maintaining air safety and security.

The other options do not provide adequate security. Keeping the passenger loading bridge attached does not prevent unauthorized access to the aircraft and can facilitate entry. Opening all cargo compartments can expose the aircraft to theft and tampering, while leaving the main cabin door unattended raises significant safety concerns, allowing free access to the cabin. Therefore, ensuring all doors and compartments are securely closed and latched is the most appropriate method for securing unattended aircraft.