Several things.....
The 727 is not centered gravity wise when empty, yes, the stairs hold up the plane. They also use a pole when the stairs are up or inoperable. it just keeps the plane level while on the ground. reason, when the plane is empty the engines weight is greater in the back vs the front so it will tip with little weight change inside.
The stairs will not lock due to the wind load on them, or all the hijackers would of jumped from a locked position. the stairs were NEVER in the locked position. the crew would have to go to the back to retract them for landing. it just never happened.
The amber light on the engineers panel tells you the stairs are not locked. the green light tells you they are in the locked position. 305 never got a green light.
Pressure will register on the gauge, these gauges are used to pressurize the plane. they are very sensitive. you have a sealed tube, basically, any disruption will register. it's not much different than closing a door in the house and the curtains move. once air is introduced to a sealed area, disruption will occur. open the car door at 10 mph and then at 90 and watch the difference wind loads create. several thousand lbs will be pushing the stairs...
One of my trucks has a camper top on it. the actuators have a load capacity of 60 lbs. while on the highway they come down to almost level due to the wind load on them. it is what it is..
