N714NW

On September 20, 1995, about 2040 Pacific daylight time, N714NW, a Cessna 150M, collided with a powerline in College Place, Washington, during an emergency descent and was destroyed. The emergency descent was precipitated by a loss of engine power during cruise flight. The private pilot and the pilot-rated passenger were not injured. Visual meteorological conditions prevailed and no flight plan had been filed. The personal flight departed from Kelso, Washington and was conducted under 14 CFR 91.

Both the pilot and the pilot rated passenger reported that they had initially departed from Walla Walla, Washington, and were destined for Kelso. At Kelso, the fuel tanks were topped off with 16.8 gallons of fuel, even though the original fuel receipt read 10 gallons. The lineman who fueled the airplane provided a 20-cent per gallon discount because he felt that he was at fault for spilling fuel on the pilot-rated passenger during the fueling. The pilot-rated passenger stated that he visually checked the fuel tanks and confirmed that the fuel tanks were topped off prior to departure. While en route back to Walla Walla, both pilots calculated their time of arrival and estimated the fuel burn at six gallons per hour, and both stated that there should have been sufficient fuel available plus a reserve. These computations were based on their perception that 10 gallons of fuel was used for the first leg of the flight from Walla Walla to Kelso.

The pilots reported that the engine lost power approximately two hours and 45 minutes into the flight. The pilot-rated passenger took over the controls and prepared for a forced landing to a lighted parking lot. The airplane was unable to reach the parking lot and the pilot opted to aim the airplane between two trees. While descending to the landing area, the airplane collided with powerlines and trees. Both pilots reported that as they were exiting the airplane, fuel was dripping from the ruptured right fuel tank.

The pilot-rated passenger stated (statement attached) that he later learned that the airplane had an "abnormally high burn rate" based on the knowledge that the actual fuel taken aboard in Kelso was 16.8 gallons, not 10 gallons. He also stated that "fuel exhaustion was the likely cause of this accident."

The Cessna Pilot's Operating Handbook states that total fuel capacity is 26 gallons with 22.5 gallons useable. Calculating a fuel burn of six gallons per hour, for two hours and 45 minutes, the airplane should have used approximately 17 gallons of fuel.

The Safety Board computed a fuel burn rate of 8.0 gallons per hour for the first leg of the flight, based on the average reported time of flight from the pilot's statement (2.2 hours) and the pilot-rated passenger's statement (2.0 hours), with a fuel consumption of 16.8 gallons. At 8.0 gallons per hour, the fuel consumed for the second leg, which lasted 2 hours and 45 minutes, would equal 22.0 gallons. This figure is 0.5 gallons less than the maximum amount of usable fuel that can be contained in the airplane.

It could not be determined if the maximum amount of useable fuel was contained in the airplane prior to the accident flight.

After the accident, the fuel tanks were inspected; the right fuel tank was ruptured and no fuel was present. The left fuel tank was intact and approximately 1-1/4 gallons of fuel remained.

The carburetor was removed and taken to a facility to be placed on a bench to test fuel flow. The test determined that the fuel flow was within the manufacturer's specifications.

The aircraft was removed by Aircraft Salvage & Rebuild, Omak, Washington. A mechanic, who inspected the engine, reported that there was no evidence found to indicate a mechanical failure or malfunction.