Why does the door pop on a f900 during climb?

There is a HUGE  amount of pressure that pushes the door outward when the airplane is pressurized.  It causes the feet to lock in place then jump a little as the fuselage grows with pressure.  The feet must be perfectly polished and clean to prevent this.  There must be a SMALL film of grease on each foot.


This is the dome shaped foot on the door.





This is  the flat foot on the air-frame. interestingly it has a slight pattern of vertical lines that are worn away on the contact patch.


the tiny polished spot is the contact patch1474911029365-546824352



The contact patch for each foot is only about a quarter inch around or less in some places



looking at the pressures applied to these feet:

Door is about 34 inches by 80 inches.

2720 square inches, 9.1 psi of pressure,

24752 pounds pushing out on the door.

10 door stops, so about 2400 lbs pushing on each stop.

.25 X. 25 inch contact patch means

2400lbs / .0625 sqin = 38000 psi pushing on each contact patch …….