Which personnel are allowed to open the L1 door from outside when the airstairs are extended?

The correct answer is that only the flight crew and engineers are permitted to open the L1 door from outside when the airstairs are extended. This is a crucial practice to maintain safety and security around the aircraft.

Flight crew members, such as pilots and cabin crew, have been trained to ensure that all safety protocols are followed. They understand the operational procedures surrounding door management, particularly in situations where the aircraft is configured for passenger boarding or deplaning. Additionally, engineers are trained personnel who may need to access the aircraft for maintenance or safety checks. Their understanding of aircraft systems makes them qualified to handle the door in these specific circumstances.

Other personnel, such as ground staff, while essential to the operations of the flight and boarding process, do not have the same level of training on the aircraft systems, particularly regarding emergency procedures related to door operations. Only allowing appropriately trained individuals to access and open the L1 door protects the crew and passengers and ensures compliance with safety regulations.