On April 17, 2004, at 1455 mountain daylight time, a Canadair CL-600-2B19, N17231, operated by Mesa Airlines, Incorporated, and doing business as America West Express Flight 412, experienced smoke in the passenger cabin while taxiing to parking at the Colorado Springs Municipal Airport (COS), Colorado Springs, Colorado. The flight crew stopped and shut down the airplane, and initiated an evacuation of the crew and passengers onto the taxiway. The captain, first officer, flight attendant, and 50 passengers on board reported no injuries. The scheduled domestic passenger flight from Phoenix, Arizona (PHX) to COS was being conducted on an instrument flight rules flight plan under the provisions of Title 14 CFR Part 121. Visual meteorological conditions prevailed at the time of the incident. The flight originated at 1240. In his written statement, the captain said that while taxiing to the gate, the flight attendant called and said there was smoke in the cabin. He said he called the flight attendant back to get more details. The flight attendant told him the cabin was full of smoke. The captain said he stopped the airplane, set the parking brake and ordered the airplane evacuation. The passengers exited the airplane and fire/rescue arrived. After verifying that all the passengers were off the airplane, the captain and the first officer deplaned. The flight attendant reported that while taxiing to the gate he noticed smoke coming from the bottom vents. He said he notified the captain, got out of his seat and went to the back of the airplane, looked around, grabbed the fire extinguisher and ran back to the front of the airplane. The flight attendant said the captain called him and told him that they were going to evacuate. The flight attendant said that when the airplane stopped he opened the door and evacuated everyone out of the airplane and onto a grassy area off the taxiway. The flight attendant described the smoke as blue in color and smelling like burning oil. A Federal Aviation Administration inspector examined the airplane at COS. He noted oil coming from a vent on the bottom aft fuselage. Oil was observed covering the bottom of the aft fuselage and tail cone. An examination of the aft equipment bay showed oil covering several components including the air conditioning packs, the cockpit voice recorder, and the flight data recorder. Company maintenance personnel determined that the right air conditioning pack had overheated. The pack was deferred in accordance with the airplane's minimum equipment list. The airplane was subsequently serviced, ground checked, cleaned up, and flown back to PHX for further examination. Further examination revealed that the fan by-pass check valve had failed causing the air conditioning pack to overheat.