An Air Wisconsin Canadair CRJ-200 on behalf of United, registration N446AW performing flight ZW-4855/UA-4855 from Portland,ME to Washington Dulles,DC (USA) with 55 people on board, was climbing out of Portland when the crew stopped the climb at FL240 due to problems with the cabin pressure. The aircraft subsequently descended to 17,000 feet and finally 11,000 feet and diverted to Burlington,VT (USA) for a safe landing about one hour after departure.
