NTSB Identification: SEA96MA043.
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Accident occurred Monday, January 15, 1996 in MALAD CITY, ID
Probable Cause Approval Date: 04/29/1997
Aircraft: Mitsubishi MU-2B-36, registration: N693PA
Injuries: 8 Fatal.
NTSB investigators traveled in support of this investigation and used data obtained from various sources to prepare this aircraft accident report.
A Mitsubishi MU-2 departed Salt Lake City, Utah, and climbed to 16,000 feet MS on an IFR flight to Pocatello, Idaho. While in cruise flight, the MU-2 encountered structural icing conditions. According to radar data, the MU-2 began slowing from a cruise speed of about 190 knots with slight deviations from heading and altitude. The airspeed decreased to about 100 knots, and the flight crew declared an unspecified emergency, then radio contact was lost. The MU-2 began a right turn, then it entered a steep descent and crashed. The pilot of a Beech 1900 (about 12 minutes in trail of the MU-2), stated that he encountered moderate rime icing at 16,000 feet. The Beech pilot activated his deice boots (3 times) and descended to 12,000 feet to exit the icing conditions. The MU-2 flight manual warned that during flight in icing conditions, stall warning devices may not be accurate and should not be relied upon; and to minimize ice accumulation, maintain a minimum cruise speed of 180 knots or exit the icing conditions. An investigation determined that the captain of the MU-2 was aware of deficiencies in the timer for the deice boots, as well as other maintenance deficiencies. The captain's medical certificate was dated 11/17/94; he was providing executive transportation for compensation under an agreement for "contractual flights," under 14 CFR 91. Although icing conditions were forecast in the destination area, no icing was forecast for the en route portion of the flight.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: continued flight by the flightcrew into icing conditions with known faulty deice equipment; structural (airframe) ice; and failure of the flight crew to maintain adequate airspeed, which resulted in the loss of aircraft control and collision with terrain. A factor relating to the accident was: the en route weather (icing) condition, which was not forecast (inaccurate forecast). Full narrative available
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