On July 27, 1998, at 1650 mountain daylight time, a Bombardier DH-8-202, N449YV, operating as America West flight 5181 from Telluride, Colorado, to Montrose, Colorado, sustained substantial damage when it collided with a parked Beech 1900D at Telluride, Airport, Telluride, Colorado. The airline transport certificated captain, first officer, flight attendant, and the 27 passengers on the DH-8 were not injured. There were no people on the Beech 1900D. The flight was operating under Title 14 CFR Part 121 and an IFR flight plan was filed. Visual meteorological conditions prevailed. According to the attached damage evaluation report provided by Field Aviation Company, Inc., Calgary, Canada, both skin (pressure vessel) and airframe damage was sustained during the impact sequence by the DH-8. According to information provided by the captain on NTSB Form 6120.1/2 (Pilot Operator Aircraft Accident Report), prior to beginning the before start checklist, he attempted to transfer hydraulic fluid from the right system to the left system. When the checklist items were confirmed, it was determined that the parking brake pressure was zero. The captain said they decided to attempt to re-pressurize the parking brake accumulator with a manual pump located in the right wheel well. The first officer had risen from his seat to accomplish this when the aircraft began to roll backwards. It rolled backward approximately 70 feet across the down sloping ramp and collided with an unmanned, empty, parked, Beech 1900D aircraft operated by Great Lakes Aviation. The investigation did not reveal a reason for the loss of accumulator pressure on the DH-8 According to information provided by FAA personnel the method the crew was using to transfer hydraulic fluid is not an approved procedure. The slope of the ramp where the event occurred was approximately two degrees and investigation revealed that the DH-8 jumped the chocks, which were on the nose landing gear wheel. According to information provided by Mesa Airlines and Beech Aircraft, parking across the slope was not feasible due to aircraft not being level, which created lateral fueling imbalance. Mesa Airlines has since changed their chocking procedures by using larger chocks and placing them on the main landing gear. It was determined during the investigation that the nose landing gear often does not have sufficient weight resting on it to prevent jumping the chocks.