N6678M

On June 30, 2002, at 1801 eastern daylight time, a Stinson 108-3, N6678M, was substantially damaged when it collided with wires and terrain during a forced landing after takeoff from Mifflintown Airport (P34), Mifflintown, Pennsylvania. The certificated commercial pilot was not injured. The two passengers received minor injuries. Visual meteorological conditions prevailed and no flight plan was filed for the local sightseeing flight conducted under 14 CFR Part 91.

According to the pilot, he was giving rides in the airplane as part of an air show that took place at the airport. The pilot performed a pre-flight inspection of the airplane, and visually inspected the fuel level in the tanks. He estimated that each 25-gallon wing tank was filled to about 3/4 capacity. He also estimated that the airplane consumed an average of 11 gallons per hour, and that he had flown the airplane for about 45 minutes prior to departing on the fourth flight of the day.

During the fourth takeoff, the airplane climbed to about 100 feet above the runway when the engine stopped producing power. The pilot adjusted the carburetor heat, and changed the fuel selector from the right tank to the left tank, but the engine would not restart.

During the subsequent forced landing, the airplane struck wires and terrain, and came to rest inverted. The pilot said he could not explain the loss of engine power.

In a subsequent telephone interview, the pilot said that the first two flights of the day were conducted with the left fuel tank selected, and that he switched to the right fuel tank during the second flight.

According to both passengers, the engine "just stopped." They each described the pilot as stating, "We're in trouble," and his manipulating switches and controls prior to the airplane striking wires, then the ground.

During a telephone interview, the owner of the airplane said that he serviced the airplane with fuel on the day prior to the air show, and that he did not fill the tanks. He serviced only one tank with 15 gallons, to bring the fuel level even with the other tank, and the fuel level in the tanks was "a little over half a tank."

The owner waited for the fuel to settle, sumped the tanks to inspect the sample for contaminants, and found none. He then departed on a 30-minute local flight, and when he returned, parked the airplane in preparation for the air show the following day. The entire flight was conducted with the left fuel tank selected. He did not service the airplane with fuel when he returned from his flight.

On the following day, the owner watched the pilot perform his preflight inspection, and saw him depart on each of the three 15-minute sightseeing flights, and then depart on the accident flight. He did not see the accident. The owner added that the engine was stopped between each flight.

When asked to describe the fuel system of the airplane, the owner stated there were two 25-gallon tanks, and that the fuel selector could only select 'Left', 'Right', or 'Off'. When he was asked again to estimate the fuel on board prior to his flight the previous day, he said there were 20 gallons of fuel in each tank, for a total of 40 gallons.

The pilot held a commercial pilot certificate with a rating for airplane single engine land. He reported approximately 800 hours of flight experience, 25 hours of which were in the accident airplane.

The pilot and the owner were provided an NTSB Form 6120.1/2, Pilot Operator Report, at the accident scene by Federal Aviation Administration (FAA) inspectors, and requested to fill it out per federal regulations, which they did not do.

The airplane was a 1949 Stinson 108-3, and it had accrued 3,332 aircraft hours. The airplane was on an annual inspection program, and its most recent annual inspection was completed on August 19, 2001.

The airplane was examined on site by the FAA inspectors. In a telephone interview, one inspector stated that it came rest inverted, and there was a strong odor of fuel and evidence of fuel spillage at the scene. Both fuel vents were separated from the airplane, and the left fuel tank was ruptured. Examination of the airplane revealed no mechanical anomalies.

The inspectors serviced the right fuel tank with about 5 gallons of fuel, and started and ran the engine on the airframe. The engine started immediately, accelerated to 1,700 rpm, and ran continuously without interruption.

The weather reported at Harrisburg, Pennsylvania, 23 miles southeast of Mifflintown, included variable winds at 3 knots. The temperature was 84 degrees F and the dewpoint was 64 degrees F. A carburetor icing probability chart revealed that ambient conditions during the time of the accident could have resulted in "serious icing at glide power."

The airplane was equipped with a Franklin 6A-4165-series engine. During the investigation of another Stinson accident, NYC02LA136, where the airplane had the same series engine, the certificated airframe and powerplants mechanic who maintained the airplane stated that the engine was particularly susceptible to carburetor icing on the ground due to the position of the air intake manifold. An engine runup was conducted shortly after that accident, and immediately afterwards, the carburetor box felt cold to the touch. At the time, the temperature was 82 degrees F and the dewpoint was 62 degrees F.