Earlier this year I was at PDX making a connection for a flight on a rainy day. A Delta 738 was on the ramp durinig it's turn. one of the F/As had opened door 1R even though there wasn't a catering truck, stairway...etc and then closed it about 15 mins later. So I finally want to clear this up! I've heard many times F/As (mainly U.S. airlines) are not supposed to open the cabin doors unless in a emergency situation. So is this acurate? Or can F/As open doors virtually any time they want, even if just to take a look at the ramp? I know airlines in the U.S. also have polocies reguarding arrivals at the Jet bridges, where they don't open the door but the gate agent does. Supposebly the F/As "crack" the doors, but what does this mean? Some refer to it as just breaking the seal of the door, Or does the door aculty have to be opend just slightly. At United I was pretty sure that gate agents knocked and then the F/As slowly began to open the doors, but last time on UA (757 ableing me to see the 2L cabin door) the flight attendant just stood back, and the door suddenly opened (by the gate agent of course) So if someone could clear all this up, or some of it at least, that would be GREAT! Thanks a lot!