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serious detriment to airspeed and altitude control, especially after the landing gear and flaps were extended. With such an accumulation of ice, it is possible that prior to or at the time the flight reached its minimum descent altitude (400 feet), the descent could not be arrested without a serious loss of airspeed. A situation of this type, it is recognized, could necessitate lowering the nose of the aircraft to regain airspeed, resulting in a rapid loss of altitude and operation below a safe terrain clearance altitude.
N61442 was equipped with a de-icing system which is normally able to cope with ice secretions on critical airframe surfaces. Because of fire and impact damage it was impossible to determine whether this system was operational or in use prior to impact. However, there were no indications noted in any of the aircraft's maintenance records pertaining to any discrepancies or malfunctions to this system. It can, therefore, be presumed that this system was capable of normal operation prior to the commencement of this flight. Any ice accretions sufficient to have caused a loss of airspeed or altitude control should have been known to the crew and, accordingly, removed from the aircraft through the use of the de-icing system.
Additionally, ice accretions sufficient to cause a loss of control resulting in ground impact 1.7 miles beyond the VOR would necessarily have had to begin accumulating considerably further back on the approach. This, in turn, would have required the use of much higher engine power settings to keep the aircraft within tolerable air-speeds, descent rates, and altitudes throughout the remainder of the approach. The sound of high engine power heard by the witnesses just prior to the crash in conjunction with the witness observations of normal engine sounds in the proximity of the VOR suggests that normal power was being employed until just prior to impact. Further, if airspeed and altitude control became critical during the approach, the landing gear and flaps would not normally have been extended until a landing on the runway was assured. If they had already been extended and a serious icing situation developed, it appears logical that one of the first steps taken by the pilot would have been the immediate retraction of any drag producing components.
Finally, the airspeed at impact, which was determined to have been approximately 134 knots, should have been more than sufficient to counteract the effects of severe airframe icing if such a situation were present.
The effects of severe turbulence combined with heavy airframe ice would, of course, constitute an additional control problem. A situation of this type would compound existing controllability problems normally associated with severe airframe ice but should not have rendered the aircraft incapable of controlled flight.
In conclusion, although existing weather conditions were conducive to airframe icing, there is insufficient evidence available to support a definitive finding in this area. Similarly, the evidence will not support any conclusion that the pilot committed a gross departure from proper piloting techniques by attempting to conduct the final portion of the approach by visual reference to the ground. The Board, therefore, is unable to determine the reason for the air-craft's departure below the approved minimum descent altitude.
