Accident Details
On July 9, 2011, at approximately 1516 Alaska daylight time, a Cessna 206 (registration N9129M) operated by Great Northern Air of Anchorage, Alaska, as a Part 135 visual flight rules cross-country passenger flight, made a forced off-airport landing about 6 miles northwest of Anchorage. The aircraft sustained substantial damage to its wings and tail during the landing, which occurred in a tundra bog. The commercial pilot and one passenger were not injured; the three other passengers sustained minor injuries. Visual meteorological conditions prevailed, and company flight following procedures were in effect. The flight had departed Lake Marie Lodge, approximately 80 miles northwest of Anchorage.
Engine Failure and Landing
According to the operator, the pilot reported a complete loss of engine power while in cruise flight. Unable to restart the engine, the pilot landed the airplane in a bog, during which it nosed over.
Fuel Management
Before departure, the pilot fueled the airplane with 26 gallons in the right main fuel tank and 8–10 gallons in the left main fuel tank. His common practice was to use the right tank for the flight and reserve the left tank. The round trip to the lodge was approximately 72 minutes of flight time plus 9 minutes of taxi. At 24 inches of manifold pressure and 2,400 rpm, the engine burned fuel at 16 gallons per hour. The flight to the lodge was uneventful. On the return, about 8 minutes from the destination, the right front seat passenger questioned the fuel gauges reading empty; the pilot explained those were auxiliary tank gauges not in use. Two minutes later, the engine lost power. The pilot switched fuel tanks, activated the emergency fuel boost pump for about 3 seconds, moved the fuel lever, turned the boost pump on, and set the mixture to full rich, but the engine did not restart. He then focused on the landing.
Passenger Accounts
The right front seat passenger stated that before takeoff he asked if there was enough fuel, noting all four gauges (main and auxiliary) were on or near empty. He said the pilot ignored the question and continued the takeoff. Another passenger in the right rear seat stated he could not see the gauges but, based on experience, believed the engine quit due to fuel exhaustion.
Post-Accident Examination
After recovery, the airplane was examined by the NTSB and an FAA inspector. The right main fuel tank was dry; the left main tank contained about 3 inches of fuel. The left header tank was full; the right header tank had a small quantity of fuel and water. Fuel was present in the engine’s fuel injection lines. The fuel vent system was clear and functional, and the fuel selector operated normally. No substantial fuel loss from leakage was observed. When a clean fuel supply was attached, the engine started and ran normally at various speeds and loads. Examination of the airplane and engine logbooks revealed no abnormalities.
Pilot Operating Handbook Information
The Pilot Operating Handbook (POH) states each main fuel tank contains 2 gallons of unusable fuel. It recommends adding 2 gallons to account for start, taxi, and takeoff. The pilot reported climbing to 1,800 feet; at climb power, that requires an additional 0.8 gallons per takeoff. Based on reported temperature and weight, the fuel burn at 24 inches and 2,400 rpm would be about 14 gallons per hour, with a 10% increase for each 10°F above standard. After fueling, the pilot made two takeoffs and landings. The minimum fuel needed for the flight (excluding the required 30-minute VFR reserve) was about 26.8 gallons.
The POH’s procedure for intentionally exhausting a fuel tank in flight states: “immediately switch to a tank containing fuel at the first indication of fuel pressure fluctuation and/or power loss. Then place the right half of the auxiliary fuel pump switch in the ON position momentarily (3 to 5 seconds) with the throttle at least 1/2 open.” It notes that excessive use of the auxiliary fuel pump and full rich mixture can cause flooding. The POH does not address minimum altitude or time required for a successful restart.
Related Information
A survey of 89 fuel-related accidents involving Cessna single-engine airplanes (following a similar accident, ANC08LA085) found that 11 involved intentionally running a tank dry and 41 involved unintentionally running a tank dry, accounting for 56% of the surveyed accidents. All 89 resulted from the pilot’s inability to restart the engine after fuel starvation. The same written procedure appeared in all Cessna single-engine, fuel-injected POHs. Surveys of Piper and Beechcraft handbooks showed they treat running a tank dry as an emergency and do not advocate it as a normal procedure. The FAR/AIM and basic flight instruction manuals direct pilots to follow manufacturer’s fuel management procedures.