This morning I was passing through IAD & had about an hour and a half to kill so I spent my time watching the activity on the ramp. I observed two United maintenance guys working on the right rear passenger door of a UAL 777. For over an hour they kept opening and closing the door dozens of times. I am wondering if anyone has any idea what the problem would have been with the door? I know the 777 has somewhat unusual passenger doors. What are the major differences between the 777 passenger doors and those on other similar aircraft? Are the 777 doors “plug” type doors? Are the 777 pax. doors more trouble to maintain than those on other aircraft?