What are Airstairs used for on an aircraft?

Airstairs are primarily designed for boarding and deplaning passengers. They serve as a staircase that allows passengers to enter and exit the aircraft directly from the ground, which is particularly useful at airports where jet bridges are not available. This facilitates a smooth and direct transition for passengers, making it an integral feature for aircraft that operate in various environments, including smaller airports.

While some other choices may reflect certain functions related to aircraft, they do not accurately describe the primary purpose of airstairs. For example, maintenance access typically involves different types of access equipment and is not a function of airstairs. Similarly, while luggage storage is an important aspect of aircraft functionality, it is unrelated to the role of airstairs. Emergency evacuations do utilize airstairs, but their fundamental purpose is for normal passenger boarding and deplaning. Therefore, the primary and correct answer highlights the essential operational role that airstairs play in passenger transport.