Accident Overview
On August 3, 2015, at about 1000 mountain daylight time, a Cessna TU206G (registration N235HM) experienced a loss of engine power and made an off-airport forced landing near Saint Ignatius, Montana. The private pilot, who was the sole occupant, was not injured. The airplane sustained substantial damage to the wings, fuselage, and empennage. The flight was operated under 14 CFR Part 91 as a personal cross-country trip, departing Bozeman, Montana, at 0812 with a planned destination of Polson, Montana. Visual meteorological conditions prevailed, and no flight plan was filed.
Pilot Report
The pilot stated he was flying to Polson to pick up a friend. About 45 minutes into the flight at a cruise altitude of 8,500 feet, the exhaust gas temperature (EGT) increased from 1,420 to 1,460 degrees Fahrenheit. He increased fuel flow, which temporarily reduced the temperature, but it soon began climbing again. Another mixture adjustment brought the temperature back down. Switching fuel tanks did not change the situation. The fuel flow gauge indicated a decrease to 17.2 gallons per hour (gph). The pilot reduced throttle and turned on the electric fuel pump at 15 gph, and the fuel flow returned to 18.2 gph for about 10 minutes. He noted the alternator light and needle fluctuating, which stopped when the electric fuel pump was turned off. The fuel flow then dropped to 14 gph. The pilot adjusted the throttle and contacted a friend who was an airplane mechanic. The mechanic offered several recommendations, including varying engine rpm, switching tanks, and adjusting the mixture control, but none produced a change in engine performance, and fuel flow continued to drop.
Engine Failure and Landing
The pilot informed his friend that he was 13 miles from Polson and intended to turn the electric fuel pump back on for the remainder of the flight. Upon activation, fuel flow went to 17.5 gph. The engine ran normally for 2 minutes, then quit; the pilot noted the fuel flow was 3 gph. He slowed the airplane to 90 knots and checked the GPS for the nearest airport, which was St. Ignatius Airport 8 nautical miles away. The airplane was descending at 800 feet per minute. When the airplane was 3 nautical miles from St. Ignatius, the pilot determined he would have to land off-airport. He aimed for a paved road with two crossing power lines and one parallel power line. He stayed high enough to clear the crossing lines, then positioned the airplane so that its right wing passed under the parallel line while clearing a ditch. After crossing, he landed on the road at 70 knots, but the brakes seemed ineffective. After rolling about 900 feet, the airplane approached a four-way junction; the pavement curved right while a gravel road continued straight. The pilot attempted to stay on the gravel road, but a fence line and bushes encroached. The left wing struck a choke cherry bush, causing the airplane to rotate left into a fence and come to a stop facing the opposite direction.
Post-Accident Examination
The pilot reported that the airplane had recently undergone an annual inspection. He contacted the mechanic who performed the inspection and described the symptoms; the mechanic suggested a loose fuel line. When the pilot's mechanic friend arrived at the accident site, they removed the top cowling and observed heavy blue stains on top of the cylinders. An FAA inspector also examined the airplane and noted blue fuel stains on top of the engine. The fuel line attached to the fuel flow transducer was found to be finger tight and leaking. Maintenance records showed that this was the first flight after maintenance performed several months earlier, during which three cylinders—including the number six cylinder (front left)—had been removed and reinstalled. The fuel line attached to the fuel flow transducer was located just above that cylinder and had been removed during the maintenance. The maintenance facility conducted a ground run with no anomalies, and the airplane was returned to the owner's hangar. It was not operated again until the accident flight.