What is a movable stairway positioned at the aircraft door to allow customers to board and deplane?

The correct answer is the rampstand. A rampstand is specifically designed as a movable stairway that facilitates customers boarding and deplaning from an aircraft. It is often used at airports where the aircraft is parked away from the terminal or in situations where a jet bridge is not available.

The rampstand is typically positioned directly at the aircraft door and provides a safe and efficient means for passengers to enter and exit the aircraft. This equipment can vary in design and height, depending on the aircraft type and the airport's infrastructure, but its primary function remains consistent across different airlines and locations.

The other options refer to different types of boarding solutions used in aviation. A jet bridge is a covered, fixed passageway that connects the terminal to the aircraft, allowing passengers to board without being exposed to the elements. The access stairway may refer to additional stairways used for service purposes, while a boarding ladder is a more primitive type of stairway often used for smaller aircraft or emergencies. These do not fully capture the specific function and mobility of a rampstand, making it the best choice in this context.