Incident Overview
On September 20, 2018, at approximately 1522 central daylight time, a Cessna TU206G, registration N756NN, sustained substantial damage during a forced landing near Brenham, Texas. The airline transport pilot and a passenger were not injured. The aircraft was operated by The United States Department of Agriculture as a public flight.
Sequence of Events
After completing photographic assignments in Central and North Texas, the pilot determined there was adequate fuel remaining to reach the destination airport with a 45-minute reserve. While circumnavigating rain showers, he began the landing approach. About 5 miles from the airport, the engine began to lose power. The pilot noticed that the left fuel tank gauge indicated a lower quantity than the right, so he switched the fuel selector valve from the left to right tank. The engine did not respond, and shortly thereafter, it lost total power. Due to the airplane's low altitude, the pilot focused on executing a forced landing without performing any emergency checklist items. The airplane struck a tree just before touchdown and hit a fence during the landing roll.
Fuel System and Data
The aircraft was equipped with long-range fuel tanks and tip tanks, with usable fuel quantities of 76 and 27 gallons, respectively. Fuel from the tip tanks was transferred to the main tanks via a transfer pump. The airplane had standard factory main fuel tank gauges and a CGR-30P electronic engine monitor (Electronics International) with a fuel totalizing feature. The pilot reported filling the airplane to capacity before departure, and data showed he set the totalizer to 103 gallons at startup. The engine operated continuously for 4 hours and 54 minutes, with an average fuel flow of 18.5 gph, fuel pressure of 10 psi, and engine speed about 2,450 rpm—all consistent with the Pilot's Operating Handbook (POH) specifications. The CGR-30P indicated fuel remaining decreased linearly; at 4 hours 51 minutes after start, 17.8 gallons remained. Over the final 3 minutes, engine speed dropped to 1,510 rpm, fuel flow to 1.6 gph, and pressure to 1.4 psi.
Post-Accident Examination
None of the four fuel tanks were breached despite left wing impact damage. Recovery personnel drained about 18 gallons of fuel from the right main tank; both tip tanks and the left main tank were empty. A mechanic, under FAA supervision, examined the airplane and found no pre-impact airframe or engine anomalies that would have precluded normal operation. The pilot reported he switched fuel tanks every hour and planned an average consumption of 18 gph. He noted that he had previously allowed a fuel tank to run dry in the accident airplane, but the engine had always restarted after switching tanks.
POH Emergency Procedures
The POH's engine failure in flight guidance included checking the fuel selector valve and quantity, enriching the mixture, turning on the auxiliary fuel pump for 3-5 seconds with throttle half open, then off, and advancing the throttle slowly. The POH permitted exhausting a fuel tank in flight but required engaging the auxiliary fuel pump briefly after selecting the fullest tank. The before landing checklist's first item was to select the fuller tank.