On March 19, 2003, about 1015 Alaska standard time, a Rockwell 500-S airplane, N903AK, sustained substantial damage when it encountered rough terrain during a forced landing following an in-flight engine fire, about 2 miles east-southeast of Chickaloon, Alaska. The airplane was being operated as a visual flight rules (VFR) local area maintenance test flight under Title 14, CFR Part 91, when the accident occurred. The airplane was operated by the State of Alaska Division of Forestry, Palmer, Alaska. The airline transport certificated pilot, and the sole passenger, were not injured. Visual meteorological conditions prevailed, and VFR flight following procedures were in effect. The flight originated at the Palmer Municipal Airport, Palmer, at 0953. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on March 19, the pilot reported the airplane had undergone extensive maintenance, including overhauls of both engines, and installation of a turbocharger system. The engines were installed by maintenance personnel under contract with the Division of Forestry. Following installation, the engines were ground-run to assess their performance, and to check for any fluid leaks. No leaks were found. An annual inspection was then completed by maintenance personnel with the Division of Forestry, and the airplane was released for a maintenance test flight. The passenger on the test flight was the mechanic who installed the engines. The pilot reported that he performed a preflight and engine runup, and no discrepancies were noted. The takeoff, with engine power settings of 30 inches of manifold pressure and 2,700 rpm, was normal. The accident flight was intended to check the turbocharging system by climbing to 12,000 feet. One of the Division of Forestry pilots observed the takeoff from the Palmer Airport. He said he noticed what appeared to be a slight vapor trail coming from the left engine of the accident airplane. He did not report his observations to the pilot. The pilot reported that while climbing through 8,000 feet, the electrical system experienced a spike, but then returned to normal. As the airplane approached 11,000 feet, the left engine's fuel pressure began to fluctuate. The manifold pressure and rpm began to decrease. The pilot feathered the propeller, and shut-off the left engine's fuel/hydraulic valve. He informed his Division of Forestry dispatcher that the flight was returning to Palmer. The passenger then noted that flames were visible coming from the left engine. The pilot began an emergency descent toward a forced landing area. He selected a gravel bar near the Matanuska River, and landed with the landing gear and flaps extended. During the landing roll, the airplane received extensive damage to the fuselage and landing gear. When the airplane came to a stop, the pilot and passenger exited the airplane and extinguished the flames from the left engine with a hand-held fire extinguisher. The pilot reported that the left engine, the left side of the fuselage, and the underside of the wing had oil streaking. A trail of oil was visible on the ground along the airplane's approach path to its final resting point. After the airplane was recovered, it was examined on March 24 and 25, 2003, by the NTSB IIC, other NTSB personnel, and an FAA airworthiness inspector. The examination revealed fire damage, melting of skin material, and sooting along the upper and left side of the left engine nacelle adjacent to the aft edge of the wing. The inboard side of the left engine cowling was scorched and fire damaged. The left inboard flap had scorching and destruction of the upper surface. Oil smudging and streaking were found along the underside of the left engine cowling, the left side of the fuselage, the underside of the inboard portion of the left wing, and the underside of the left horizontal stabilizer. The underside of the wing, between the nacelle and the fuselage was fire damaged. The left engine firewall had scorching and spattering of metal and fire damage at the lower inboard edge of the firewall. The left engine turbocharger inlet air scat tubing was destroyed by fire, along with the oil return line between the bottom of the turbocharger and the aft side of the engine case. This portion of the engine cowling had the most extensive oil deposits and streaking, indicating the breached portion of the oil return line allowed engine oil to vent to the atmosphere. The engine still contained about 6 quarts of oil. The upper oil supply line to the turbocharger was sooted, but not breached. The turbine was free without restriction upon hand rotation. Fire damage and sooting were concentrated on the aft accessory case portion of the engine, centered near the engine driven fuel pump. Examination of the fuel pump disclosed that the fuel line, from the left wing fuel tank to the fuel pump, was not connected to the pump. The threaded fitting of the line was hanging below the pump, and had sooting on the interior of the fitting. The mating inlet nipple of the fuel pump had extensive sooting of the exposed treads. The interior portion of the "L" shaped nipple was sooted. The fuel line from the fuel pump to the engine servo was attached to the pump. It was sooted and scorched, but not breached.