NTSB Identification: SEA08FA006.
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Accident occurred Sunday, October 07, 2007 in Ekalaka, MT
Probable Cause Approval Date: 09/26/2008
Aircraft: Cessna 310N, registration: N85WT
Injuries: 2 Fatal.
NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The instrument-rated private pilot was on a cross-country flight in instrument meteorological conditions. About 40 minutes after departure the pilot reported to air traffic control (ATC) that he was encountering icing conditions at his cruise altitude of 13,000 feet and requested a lower altitude. The pilot was cleared to descend to 11,000 feet. The pilot continued to encounter icing conditions and was cleared to descend to lower altitudes. About 15 minutes after the pilot's initial report of icing conditions, he transmitted "headed towards the runway" followed by "...going down...troubles with engine." No additional communication from the accident pilot was received. The wreckage was located later that day in an open field about 2 miles west of a private airstrip. Post accident examination of the airframe and engine revealed no evidence of mechanical malfunction or anomaly. Ground scars and wreckage signatures were consistent with a stall/mush into the terrain. Weather forecasts and pilot reports for the pilot's intended route of flight indicated icing and widespread instrument meteorological conditions. The pilot received a weather briefing prior to the flight; however, it was limited by his request to wind, temperature aloft forecasts and METAR observations for his route of flight. FAA Advisory Circular 91-51A states, in part, "The most hazardous aspect of structural icing is its aerodynamic effects. Ice can alter the shape of an airfoil. This can cause control problems, change the angle of attack at which the aircraft stalls, and cause the aircraft to stall at a significantly higher airspeed..." The AC additionally states "Flight into known or potential icing situations without thorough knowledge of icing and its effects and appropriate training and experience in use of deice and anti-ice systems should be avoided." According to the manufacturer, the airplane was not certified or equipped for flight into known icing conditions. It is probable that the airplane was unable to maintain an adequate airspeed during the descent for landing and stalled short of the runway.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot's improper in-flight planning/decision, his continued flight into adverse weather (icing conditions), and failure to maintain an adequate airspeed during the emergency descent for landing. Contributing to the accident were the forecast icing conditions. Full narrative available
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