Accident Details
On July 21, 2014, at approximately 1325 mountain daylight time, the wreckage of a Cessna 150M airplane, registration N66255, was discovered at the west end of Russian Flat Airport in Russian Flat, Montana, by a driver passing by on a nearby highway. The airplane, registered to Cowdog Flyers LLC, was operated by a commercial pilot under 14 CFR Part 91. The pilot, the sole occupant, sustained fatal injuries, and the airplane sustained substantial damage. Visual meteorological conditions prevailed, and no flight plan had been filed. The flight originated from Bozeman, Montana, at about 1236.
Wreckage Examination
An FAA aviation safety inspector reported that the airplane was located approximately 570 feet from the end of runway 25. The wreckage lay in an open swamp area, with the engine and nose partially submerged in water. The airplane impacted the water in a near vertical attitude. The fuselage and wings sustained substantial damage.
The right wing remained attached, with extensive spanwise leading edge aft crushing. The lift strut was undamaged. The right wing was displaced about 60 degrees aft of the lateral axis. The left wing also remained attached, with relatively little impact damage, and was displaced about 60 degrees forward of the lateral axis. Both flaps were found in the retracted position. Flight control continuity could not be established on scene due to a lack of tension on the direct control cables. The tail structure was displaced about 50 degrees right of the longitudinal axis.
The propeller remained attached to the engine crankshaft. One blade exhibited substantial torsional "S" twisting and chordwise scratching, while the other had leading edge gouging and chordwise scratching. The airframe and engine examination revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.
Weather Conditions
Convective rain showers and thunderstorm activity were prevalent around the accident site and central Montana at the time. Weather radar imagery showed a rain shower near the accident site, and satellite data confirmed the movement of these showers and thunderstorms from west to east. Non-official surface observation data from a nearby location indicated the strongest wind and gusts around the estimated accident time. When rain showers and thunderstorms passed official sites, surface wind gusts reached 31 knots. The forecast valid at the accident time warned of rain showers and thunderstorms in the central weather service unit advisory (CWA), Area Forecast, and closest terminal area forecast.
Remarks in the Airport Facilities Directory for Russian Flat Airport noted that Runway 25 had a 2% uphill slope to the west and recommended takeoffs on runway 07 and landings on runway 25, conditions permitting. There was also a caution to check density altitude due to the airport's high elevation.
Density Altitude Considerations
The closest non-official weather station, South Fork Judith, located about 1 mile east of the accident site at an elevation of 6,300 feet, reported a temperature of 68°F and a dewpoint of 47°F. Using the closest altimeter setting of 30.00 inches from Lewistown Municipal Airport (44 miles northeast) and the field elevation of 6,336 feet, the pressure altitude was calculated at about 6,256 feet. The density altitude at the time of the accident was approximately 8,296 feet.
A review of the manufacturer's Flaps Retracted Takeoff Distance chart showed that the weather conditions exceeded the chart's performance parameters, as the maximum altitude for which takeoff data was supplied was 7,500 feet—796 feet lower than the density altitude. Furthermore, the data did not include penalties or enhancements for sloped or wet grass runways.
According to the FAA's Airplane Flying Handbook, an increase in density altitude can result in greater takeoff speed, decreased thrust, reduced net accelerating force, and an immediate decrease in power output for unsupercharged reciprocating engines.