On October 18, 2010, about 1425 mountain standard time, a Bombardier, Inc., CL-600-2B19, N938SW, operated by SkyWest Airlines as United Express flight #6522, landed at the Phoenix Sky Harbor International Airport, Phoenix, Arizona (PHX), under the provisions of 14 Code of Federal Regulations Part 121. The scheduled domestic passenger flight taxied to the terminal gate, where the main passenger cabin door (MCD) became jammed shut and would not open. The airplane sustained minor damage to the MCD. There were no injuries to the 2 airline transport pilots, 1 flight attendant, or the 50 passengers. Visual weather conditions prevailed and an instrument flight rules plan was filed for the flight, which originated from Los Angeles International Airport, Los Angeles, California (LAX), about 1241 Pacific daylight time, with an intended destination of Phoenix. The captain reported to a National Transportation Safety Board (NTSB) investigator who was on the flight, that the MCD's power assist motor was inoperative when the flight was dispatched from LAX. He stated that he had been authorized to fly the airplane to PHX with the MCD's deferred maintenance status, and the flight was performed in accordance with SkyWest's minimum equipment list (MEL) procedures. The captain further reported that approaching PHX, he advised his company that ground personnel assistance would be required to open the door. The captain stated that he anticipated the MCD would open freely upon receiving assistance from personnel outside the airplane. A United Airlines employee who marshaled the airplane to the gate stated that after he chalked the nose wheel, the captain signaled him to open the MCD. The marshaller stated that he pulled on the latch to open the door, but it would not open. He followed the procedures he has used on numerous occasions to open this type of airplane door. However, on this occasion, he could not open the door. A captain, who was waiting on the jet bridge to fly the airplane on its next scheduled leg also attempted to open the door and was unsuccessful. This malfunction precluded passengers from immediately exiting the airplane. Shortly after, the incident captain exited the cockpit to assess the problem. The captain tried pushing on the door while personnel outside the airplane were pulling it open and while he was lifting the door handle from the inside. The captain stated "nothing worked." And he then returned to the cockpit and made a public address announcement to the passengers, stating that because of technical problems with the door, there would be a delay exiting the airplane. The captain opened the galley service door on the opposite of the airplane to acquire direct communication with outside ramp personnel. The captain said that his plan was to have the ramp personnel stow the door handle from the outside, and this would allow him to try opening the MCD from the inside. Following this plan, the captain pushed his shoulder against the door and used some exerted force. The door opened and extended beyond its normal limits and rotated downward until it impacted the tarmac. The elapsed time from the airplane arriving at the gate until the MCD was opened was about 10 minutes. The MCD sustained damage to its supporting wheel assembly and power assist motor cable. The cable was found stuck inside the door.