NTSB Identification: SEA05LA066.
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Accident occurred Thursday, March 24, 2005 in Cascade, MT
Probable Cause Approval Date: 10/27/2005
Aircraft: Abbott Glasair Legend, registration: C-GUTT
Injuries: 1 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The aircraft was descending in light snow, at idle power, on an ILS approach when it passed through an area where the outside air temperature increased from eight degrees Fahrenheit to thirty-two degrees Fahrenheit in a time span of about 20 seconds. Soon thereafter the aircraft's engine suddenly stopped producing power. Because he was unable to get the engine restarted, he descended straight ahead, and eventually lowered the landing gear for an attempted off-field power-off landing. Although he was able to make an uneventful touchdown in a rough open snow-covered field, as the aircraft began to roll, its wheels sunk into the snow, and all three gear legs collapsed. When the gear collapsed the airframe contacted the terrain and sustained substantial damage. After the accident, recorded data was downloaded from the aircraft's electronic engine fuel control system, and it was determined that at the time of the power loss, fuel pressure to the engine was within normal parameters, but N1 rpm and ITT (inter-turbine-temperature) were dropping. An inspection of the engine did not reveal an evidence of any anomaly or malfunction, but it was discovered that just upstream from the compressor, and just downstream from the NACA-form engine air inlet ducts, was a protective screen with one-eight inch diameter openings in its surface. The loss of power during the sudden OAT increase was consistent with the previously dry snow becoming wet and heavy during the rapid temperature increase, and then accumulating on the aforementioned protective screen, starving the engine of inlet air.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The accumulation of wet snow on the engine inlet assembly protection screen during a rapid increase in outside air temperature, while on an instrument approach for landing. Factors include falling snow, a sudden and significant increase in outside air temperature, and rough, snow covered terrain in the area where the pilot found it necessary to attempt a forced landing. Full narrative available
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