| Crash location | 61.783333°N, 156.591944°W |
| Nearest city | Stony River, AK
61.783056°N, 156.588056°W 0.1 miles away |
| Tail number | N2125F |
|---|---|
| Accident date | 05 Jun 2005 |
| Aircraft type | Cessna 206 |
| Additional details: | None |
On June 5, 2005, about 1715 Alaska daylight time, a wheel-equipped Cessna 206 airplane, N2125F, sustained substantial damage when it collided with trees during a forced landing following a loss of engine power while in cruise flight, about 9 miles west of Stony River, Alaska. The airplane was being operated as a visual flight rules (VFR) cross-country personal flight under Title 14, CFR Part 91, when the accident occurred. The certificated private pilot, and the two passengers, sustained minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated at the Palmer Municipal Airport, Palmer, Alaska, about 1520, and was en route to Aniak, Alaska.
During a telephone conversation with the National Transportation Safety Board investigator-in-charge on June 6, the pilot reported that while in cruise flight about 4,000 feet above the ground, all engine power was lost. He said that while performing emergency engine procedures he activated the electric auxiliary fuel pump, and switched the fuel valve from the left tank to the right tank, even though each fuel tank contained adequate fuel. The pilot said while performing the emergency engine procedures, he noted that the engine fuel pressure was reading zero. He was unable to restore engine power, and selected an open area surrounded by trees as an emergency landing area. The airplane landed short of the intended landing site, struck a large stand of trees, and nosed over. The airplane sustained substantial damage to the wings, fuselage, and empennage.
The pilot stated during the June 6 telephone conversation that about a month before the accident flight, he had recurring difficulty starting the airplane's engine. He said that he was unable to prime the engine with fuel due to a lack of fuel pressure from the electric fuel boost pump, but assumed the problem was associated with a fuel system vapor-lock condition. He reported that once the engine was started, it continued to operate normally.
The accident airplane was equipped with a Dukes, Inc., 24 volt, rotary style electric auxiliary fuel pump. A 2-inch long drive shaft connects the electric motor to the rotary pump assembly. A 1/2-inch diameter rotor, located within the pump assembly, is equipped with 4 nylatron vanes. A 1/4-inch long shear pin interconnects the rotor to the drive shaft during fuel boost pump operation.
On December 13, under the direction of the NTSB IIC, the accident airplane's electric auxiliary fuel pump was placed on a fuel system test stand at Alaskan Aircraft Engines, Inc., Anchorage, Alaska. When electrical power was applied to the pump assembly, the electric motor portion of the pump operated normally. However, during initial operation, intermittent and erratic fuel pressure fluctuations were observed, followed by a total loss of fuel pressure. The electric motor continued to operate after all fuel pressure was lost. The electric auxiliary fuel pump was disassembled, which disclosed that the 1/4-inch long shear pin was fractured. Examination of the 2-inch long drive shaft revealed that a portion of the remaining shear pin would intermittently engage the 1/2-inch diameter rotor, but failed to provide a continuous connection between the electric motor and the rotor assembly.
On December 14, under the direction of an NTSB air safety investigator, the accident airplane's engine driven fuel pump assembly was placed on a fuel system test stand at Firewall Forward, Inc., Fort Collins, Colorado. The NTSB investigator reported "a disruption (air/foam) in the output fuel flow" while the engine driven fuel pump was being operated on the fuel system test stand. The investigator noted that when an auxiliary fuel pump was activated, a pump that simulates the airplane's electric auxiliary fuel pump, the engine driven fuel pump operated normally. The fuel pump was subsequently disassembled, which revealed that a 1/8-inch metal shaving blocked the vapor injector orifice. The metal shaving was then removed from the vapor injector orifice, the pump was reassembled, and again placed on the fuel system test stand. The pump then operated in accordance with the manufacturer's specifications.
A partially blocked fuel pump, which resulted in a loss of engine power while in cruise flight. A factor associated with the accident was an inoperative electric auxiliary fuel pump.