I have gotten an answer saying that the stairs are not an universal height and can be adjusted due to passenger weight and the weight on the plane. What if this gap occurs as the passengers are climbing into the aircraft? As I would expect that the plane would be heavier and therefore a gap where the airstairs are below the entrance is unusual?
Additionally, what is the mechanism that is used to adjust the stairs to fit to the height of the plane?
Stairs are of course not of fixed height and they can be adjusted either mechanically or hydraulically. Though weight of empty aircraft and that of fully laden aircraft may greatly vary, the height of cabin entrance changes by only few centimeters. (only as much as the landing gears and tyres can get compressed). As the passengers get in, this depression in height is not even observable. The stairs are positioned at the cabin entrance at a pre-determined height specified for the type of aircraft taking into account the possible reduction in height of the cabin entrance. So it really does not matter, how many passengers get in or how much is the laden weight of the aircraft. The difference in height of cabin entrance and the top rung of the stairs will always be much less than a few centimeters and average person can easily negotiate without even acknowledging the difference.
