On March 15, 1999, at 2146 mountain standard time, a Cessna 320D, N4127T, operated by Star West Aviation of Evanston, Wyoming, was substantially damaged when it collided with terrain following a partial loss of power on the left engine during final approach to landing at Jefferson County (Jeffco) Airport, Broomfield, Colorado. The commercial pilot, the sole occupant aboard, was not injured. The aircraft was being operated as a non-scheduled domestic cargo flight under Title 14 CFR Part 135, and an IFR flight plan had been filed. The flight originated from Cheyenne, Wyoming, approximately 51 minutes before the accident. Visual meteorological conditions prevailed. According to the pilot, while 25 nautical miles north of Jeffco Airport and level at 8,000 feet, there was a momentary surge of power on the left engine. She turned on the fuel boost pumps and switched from the auxiliary to the main tanks. Approximately one to two minutes later, the left engine began to surge again and went to near zero thrust; however, the rpm still had some indication of power. She verified that the loss of power was on the left engine. She then checked to make sure that the fuel pumps were still on HIGH and that the fuel selectors were in the detent position on the main tanks. She was level at 7,500 feet and on a direct course for the airport when the power was substantially restored, and she returned power to the right engine to stabilize the yawing. She received clearance to land on runway 29R with a right base entry. While approximately four miles from the airport, the power on the left engine began to surge again. While two miles from final approach, the left engine again lost power. The aircraft began rolling and yawing with full right rudder and the left wing raised. The pilot never declared an emergency, and stated that she did not feather the propeller because the engine continued to produce partial thrust. As the aircraft crossed the runway threshold, she reduced the throttles, but the nose continued to yaw toward the left engine with full right rudder applied. As she flared for landing, the aircraft veered to the left. She stated that she had neither the altitude nor the airspeed to correct the situation before touching down. The aircraft departed the runway to the left, and came to rest approximately 75 feet off the runway into the grass. The left landing gear was separated from the aircraft, the left and right propeller blades were bent, and the left wing spar was broken. The total fuel capacity in the Cessna 320D is 140 gallons; 50 gallons in the each of the main tanks, and 20 gallons in the auxiliary tanks. According to an airport employee, he "topped off" N4127T with 79.3 gallons of fuel prior to the aircraft's departure from Evanston-Uinta County Burns Field Airport, the airplane's home base. The pilot's route of flight was from Evanston to Riverton, then to Casper, Cheyenne, and lastly to her final destination of Broomfield, Colorado. The total time en route was 2 hours and 50 minutes. Calculating an average fuel burn of 31 gallons per hour, the aircraft should have had 53.2 gallons of fuel remaining upon landing at Jeffco. The day following the accident, fuel was found in the right main fuel tank; however, the left wing spar had been broken and the left tank was compromised during the landing sequence. The presence of fuel in the left main fuel tank could not be verified. On March 30, 1999, the left engine, without the turbocharger installed, was run in a test cell at the facilities of Firewall Forward in Fort Collins, Colorado. The engine operated up to the maximum available power, and no discrepancies were observed. A flow check was performed on the fuel injectors lines, and the flow on each nozzle appeared evenly distributed. The turbocharger was examined on July 14, 1999, at AlliedSignal Aerospace's test facilities in Torrence, California. No abnormalities were found.