Date: 201308
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: Turbulence; 10
Light: Daylight
Aircraft: Cessna Stationair/Turbo Stationair 6
Operator: Government
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Initial Approach
Airspace: Class E ZZZ
ATC / advisory: TRACON ZZZ
Aircraft component: Fuel System
Component problem: Design; Improperly Operated
Reporter organization: Government
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Commercial; Flight Crew Instrument; Flight Crew Multiengine
Human factors: Distraction; Situational Awareness; Time Pressure; Troubleshooting; Workload
Anomaly: Aircraft Equipment Problem Critical; Inflight Event / Encounter Fuel Issue
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Landed in Emergency Condition; General Maintenance Action
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: Pilot was enroute. I had received ATIS; contacted ATC; and received a runway assignment. The aircraft was operating under a reserve fuel situation. One tank was very low and the other approximately 1/4 full. When the engine began to run rough I switched to the fuller tank. This seemed to resolve the engine roughness; but I decided to proceed to a GA airport I had just passed over; rather than fly over a heavily populated area with a rough running engine. I informed ATC of this and was told to proceed direct to my divert airport; squawk 1200; radar service was terminated; and frequency change to advisory approved. ATC also mentioned some traffic; but it was not a factor and was not relevant to what transpired. After reversing course; changing frequencies to CTAF; and flying southbound for a couple of miles; the engine began running rough again. I again switched fuel tanks. In hindsight; this was a mistake as I had gone back to the low tank. At this point the engine began to lose power and the aircraft lost altitude. I activated the electric boost pump; but this did not restore power. Since the aircraft had descended to approximately 1;000 FT AGL; I began looking for a landing site. I considered landing on the interstate; which was directly below me; but the traffic was too heavy and there was an overpass near the anticipated landing site; so I abandoned that idea and looked for a flat field. Luckily; I spotted a soybean field about 1/2 mile east of an interstate highway. Since the wind was reported out of the northeast; I elected to land in the direction of the crop rows to the north. I extended the landing flaps to full (40 degrees) and executed a force landing in this field. The aircraft came to a stop in about 600 FT from the point of touchdown. Thankfully; there was no damage to the aircraft and no injury to the pilot. The pilot contacted the company flight department; who informed the ATC; state police; and FAA FSDO of the incident. Mechanics were dispatched to the landing site to evaluate the aircraft. They disconnected the fuel line and activated the electric boost pump; which produced a steady; extended stream on both settings. The fuel sumps were drained and no evidence of water observed. The engine was started and run up for about 5 minutes. Upon visual inspection of the tanks it was observed that the right tank was down to the minimum (unusable) level. The mechanics believe that air was introduced into the fuel line when the low tank got to the unusable level. Unfortunately; this aircraft has only a left; right; and off fuel selector setting. If there was a 'both' setting; such as exists on most of the other aircraft in the company fleet; this could have been avoided. Additionally; the mechanics stated that if the pilot had pushed and held the electric fuel boost pump; rather than just pushing the switch and releasing; the air could have been purged from the fuel line and the flight continued without further incident. Pushing and releasing the fuel boost pump switch only activates the high pump briefly and the low pump continuously. Pushing and holding this switch maintains the high pump which is required to purge air from the fuel line. Regardless; the aircraft was towed a short distance by a local farmer using a tow bar borrowed from the airport to the closest road; fuel was added to the low tank; and the aircraft flown back to the departure uneventfully. Again; this was an avoidable situation. If the aircraft had a 'both' fuel selector setting; or the pilot not allowed the right fuel tank to get so low before switching tanks; or the pilot had continually held down the electric fuel boost pump switch to purge the air in the fuel line; this forced landing may have been avoided. Fortunately; this story had a happy ending and provided a valuable learning experience.




Synopsis: A C206 fuel line filled with air after the selected tank quantity became low; but because the electric fuel pump on LOW was unable to purge the line after the other tank was selected; the pilot landed safely off airport with engine producing minimum power.