Cascade, MT, USA
C-GUTT
Abbott Glasair Legend
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.
On March 24, 2005, approximately 1115 mountain standard time, an experimental Abbott Glasair Legend, C-GUTT, experienced a collapse of its landing gear during a forced landing in a rough snow-covered field about six miles northeast of Cascade, Montana. The Canadian certified commercial pilot, who was the sole occupant, was not injured, but the aircraft, which is owned and operated by the pilot, sustained substantial damage. The 14 CFR Part 91 personal pleasure flight, which departed Springbank, Alberta, Canada, about 75 minutes prior to the accident, was being operated in instrument meteorological conditions, and was on an IFR flight plan. The intended destination was Great Falls, Montana, and the aircraft was on an instrument approach to Great Falls International Airport at the time of the accident. There was no report of an ELT activation. According to the pilot, the aircraft was descending in light snow, at idle power, on an ILS approach to runway 03 at Great Falls International Airport 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 any evidence of an anomaly or malfunction, but it was discovered that just upstream from the compressor, and just downstream from the NACA-form engine inlet ducts, was a protective screen with one-eight inch diameter openings in its surface. It was the opinion of both the mechanics that maintained the aircraft, and the engine shop that assisted in the post accident inspection and test-run of the engine, that during the sudden OAT increase, the previously dry snow became wet and heavy, and then accumulated on the aforementioned protective screen, starving the engine of inlet air.
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.
Source: NTSB Aviation Accident Database
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