NTSB Factual Report

On May 10, 2009, about 1310 Pacific daylight time, a Cessna U206E, N1457M, experienced a total loss of engine power while cruising about 5 miles north of Oroville, California. The private pilot made a forced landing in an open field. The airplane's nose gear broke off as the airplane decelerated over uneven terrain, the firewall was bent, and the airplane was substantially damaged. The private pilot was not injured during the personal flight that was performed in the airplane, which he co-owned. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight was performed under the provisions of 14 Code of Federal Regulations Part 91, and it originated from Marysville, California, about 1230.

The pilot reported to the National Transportation Safety Board investigator that when his flight initiated, the airplane's fuel tanks contained a total of 55 gallons of 100 LL fuel. After takeoff, he performed two uneventful touch-and-go landings. Thereafter, he climbed to a 2,600-foot mean sea level (msl) cruise altitude.

There were no clouds in the sky, and the wind was calm. The visibility was 100 miles.

According to the pilot, while cruising the engine suddenly "died, as if the [ignition] key were shut off." Immediately thereafter, engine power returned without his taking action, and then the engine died completely.

The pilot stated that he responded to the emergency by switching fuel tanks and also activating the electric fuel pump. The propeller continued to windmill. Due to the airplane's low altitude, he then concentrated on executing the forced landing. His efforts at restarting the engine were not successful, and he landed the airplane on the nearby rough terrain, about 1,100 feet msl.

Airplane recovery personnel reported to the Safety Board investigator finding evidence of fuel in all of the airplane's fuel tanks. The airplane was recovered from the accident site and examined by Federal Aviation Administration (FAA) personnel.

In pertinent part, FAA personnel reported observing minimal propeller blade damage, which they opined was consistent with low or no engine power at impact. Control continuity between the cockpit's engine controls and the engine was confirmed. No anomalies were noted with the magnetos, examined spark plugs, cylinders, or internal engine components during rotation of the engine's crankshaft. The integrity of the fuel system was confirmed between the wings and the engine. The fuel vents in the wings and the bladder tanks were examined, and no blockages were noted.

To ascertain the functionality of the powerplant, an FAA principal maintenance inspector test ran the engine. The FAA inspector reported that the electric fuel pump operated normally, and the engine properly started. Thereafter, it was test run for 12 minutes. No anomalies were noted. At the conclusion of the examination, the FAA inspector reported finding no evidence indicating why the reported power loss occurred.

The accident airplane was equipped with a J.P. Instruments, Inc. (JPI), engine data management (EDM-800) system that recorded various engine operating conditions. Following the FAA's engine test run, the EDM-800 was removed from the airplane. Under the Safety Board's supervision, its retained memory was downloaded by JPI's personnel at their manufacturing facility. JPI personnel reported to the Safety Board investigator that the instrument appeared undamaged, and the downloaded file contained data that did not appear corrupt.

The downloaded file of the accident flight was reviewed by Safety Board personnel. A data graph showing the accident flight is included in the docket for this accident report. In pertinent part, the graph includes the following data for Time, Exhaust Gas Temperature (#1 cylinder, degrees Fahrenheit) Fuel Flow, and Revolutions Per Minute:

*TIME EGT FF RPM NOTES

2117:54 1378 17.6 2465 (EGT remained bet. 1378 & less than 1417)

2124:12 1354 16.2 2345 (EGT rose to 1417 at 2124:24)

2124:24 1417 11.2 2339 (Peak EGT occurred here)

2124:30 1007 0.9 2130

2124:36 572 0.0 1937

2125:42 241 0.0 0

*See the docket for information regarding event times and all recorded data.

JPI's Pilot's Guide indicates that retarding the mixture control changes the fuel/air ratio and hence the exhaust gas temperature. The Guide states: "As the mixture is leaned, EGT rises to a peak temperature, and then drops as the mixture is further leaned."

NTSB Probable Cause

A total loss of engine power during cruise flight due to an excessively lean mixture for undetermined reasons.