On January 4, 2003, approximately 0900 mountain standard time, a Hawker Siddeley HS-125-700A, N270KA, operated by Key Air, Incorporated, and piloted by an airline transport pilot, encountered smoke in the cockpit during engine start in preparation for takeoff at the Telluride Regional Airport, Telluride, Colorado. The airplane was shut down and an emergency evacuation was accomplished. Airport fire department units responded to the airplane. The captain, first officer, and four passengers on board were not injured. Visual meteorological conditions prevailed at the time of the incident. The unscheduled, domestic business flight from Telluride, Colorado, to Oxford, Connecticut, was being conducted on an instrument flight rules plan under the provisions of Title 14 CFR Part 135. The cross-country flight was originating at the time of the incident. According to the company, the crew had started the auxiliary power unit (APU) approximately 30 minutes prior to starting engines. The crew and 4 passengers were on board the airplane. The crew started the number 2 engine and smelled smoke. They turned around to observe smoke in the cabin. The crew shut down the number 2 engine, the APU, and all electrical switches. The crew and passengers got off the airplane through the main cabin door. An inspection of the airplane revealed a venturi fan unit, located aft of the rear cabin bulkhead, was charred. Insulation, wires, and air ducts in the immediate vicinity of the unit were also charred. No other anomalies were found. An examination of the venturi fan unit showed the motor had overheated and subsequently failed. According to the company, the venturi unit was installed in 1999. The unit, part number 207640-10, serial number 53-3671, was an older model identified by Hawker, in 1994, as being subject to in-service failure due to the fan motor overheating and resulting in smoke generation in the cabin. On February 22, 1994, Hawker Aircraft issued an Alert Service Bulletin requiring the inspection of all existing units at that time. A few months later, an Airworthiness Directive was issued requiring a minimum inspection period of 4 years on the unit. The company's Chief Pilot stated that a new thermal fuse unit was produced in 1994 or 1995, which senses heat earlier and shuts the unit down before tripping the circuit breaker. Following the incident, the company replaced the venturi units in its other two Hawker airplanes with the thermal fuse type unit.