SEA97FA070

The pilot received both a standard preflight weather briefing and an inflight weather update that indicated he should expect icing, while in clouds or in precipitation, which was forecast to be along his route. While en route, he flew into clouds, and the airplane began picking up ice. For at least ten minutes after the initial onset of airframe ice accumulation, the pilot continued toward his destination. He elected to reverse course, but before he was able to exit the cloud formation, the ice accumulation became 'significant.' His last two radio transmissions indicated that the aircraft was inverted and that he was in trouble and '...going down.'

History of flight

On March 7, 1997, approximately 1635 mountain standard time, a Piper PA-24-250, N7583P, impacted the terrain about 40 miles north of Boise, Idaho. The instrument rated private pilot and his two passengers received fatal injuries, and the aircraft was destroyed. The FAR Part 91 personal pleasure flight, which had departed Jerome, Idaho, about one hour and ten minutes earlier, was en route to Pullman, Washington, in IFR conditions at the time of the accident. The pilot, who was on an IFR flight plan, received a telephonic weather briefing prior to departure, and also received an inflight update about 25 minutes prior to the accident.

On the day of the accident, the pilot made telephone contact with Boise Automated Flight Service Station at 1341 and received a full standard weather briefing. At the end of that briefing, he filed an IFR flight plan from Jerome, Idaho, to Pullman, Washington. At 1525, while still on the ground at Jerome, the pilot called Twin Falls Approach requesting his IFR clearance. At 1527, he received his clearance, and then departed Jerome at 1529. The flight was worked by Twin Falls Approach until passing 9,000 feet, when the pilot was handed off to Salt Lake City Center. At 1603, the aircraft leveled at 13,000 feet, and approximately five minutes later the pilot contacted Cedar City Automated Flight Service Station in order to get a weather update. At 1608, Salt Lake Center transmitted a frequency change for the flight, but since the pilot was talking with Flight Service, he did not respond. At 1610, the pilot contacted Center and said the he had been talking to Flight Service. At that time Center gave the pilot the frequency change, and after making contact on the new frequency, he was given the Baker altimeter setting. There was no further contact between Center and the pilot until 1618, when the pilot reported "...we're picking up some ice, like to try one four thousand." Center then cleared the flight to one four thousand and asked the pilot for the type and intensity of the ice. The pilot responded with "Comanche eight three papa picking up some rime ice and its not real intense, but its a little bit." Center then asked the pilot to let the controller know when he got out of the ice, and the pilot responded with "...climbing to one four thousand." At 1520, the pilot reported he was "...approaching one three thousand five hundred, coming out of the clouds." For approximately eight minutes there were no communications between Center and the pilot. Then at 1528, the pilot transmitted "...we're about as high as we want to go and we're in some ice, and I think we're going to make a one eighty." At that point Center asked the pilot if he wanted to go to Boise, but he replied that he would go back to Twin Falls. Center then cleared the pilot direct to Twin Falls and asked what altitude he wanted. The pilot responded with to the altitude inquiry with "... I'll stay at one four thousand till we get back on top." About one minute later Center asked the pilot "...what are you getting for ice now," and the pilot responded with " Uh, still picking up rime ice, but it's significant." At 1530, Center cleared the flight to Twin Falls via Victor two ninety three, and asked if the pilot was going to be able to maintain one four thousand. The pilot said that he could, and then there was no further contact until 1535:33, when the pilot transmitted "Salt Lake Center, Comanche eight three papa." At 1535:37 and 1535:50, Center responded with "Comanche eight three papa, go ahead," and at 1535:52 the pilot transmitted "Comanche, Comanche eight three, Comanche eight three papa, we're inverted, we're in trouble." At 1535:59 the controller asked if the aircraft was upside down and asked if the pilot could hear center. Then at 1536:11, the pilot transmitted "Comanche eight three papa hears Salt Lake, we're inverted, we're going down." Center heard no further transmissions from the pilot, and the last transponder radar data block showed the aircraft descending through 13,000 feet.

Meteorological information

During the preflight weather briefing, Flight Service advised the pilot that there were Airmets in effect at the time of the briefing, and recommended that he "...double-check the new Airmets ..." prior to departure. The Airmets in effect at the time of the briefing indicated occasional mountain obscuration, occasional moderate turbulence below 18,000 feet, light occasional moderate rime or mixed icing in clouds or in precipitation form the freezing level up to 16,000 feet. The synopsis portion of the briefing showed a low pressure system moving across the route, with a cold front that had moved into western Idaho at 1100 that morning. The air mass following behind the front was reported as unstable, with a freezing level between 3,000 and 4,000 feet. The terminal forecast for Lewiston (Pullman was not available) was for surface winds of 15 knots gusting to 25 knots, visibility more than six miles, 4,000 scattered, ceiling 5,000 broken, with occasional conditions of ceiling 4,000 broken, thunderstorms and light rain. The en route portion called for broken layers at 7,000 and 12,000 feet, with tops to flight level two two zero, and widely scattered light rain and light snow showers.

When the pilot contacted Cedar City Flight Service for his inflight update, he was advised that there were current airmets (Sierra update 3, Tango update 5, and Zulu update 3) which called for occasional moderate turbulence, mountain obscuration, and light, occasional moderate rime/mixed icing in clouds and precipitation. The pilot responded that it looked okay at 13,000 feet, and that he would stay on top. The briefer then advised the pilot that there would be solid clouds for the rest of route, and that the tops would be higher to the north.

Wreckage and impact information

The aircraft impacted snow-covered rocky terrain near the 6,850 foot level of a 7,950 foot high ridge, about one-half mile north of Deadwood Fire Lookout Station . The slope of the terrain was approximately 45 degrees, and according to search-and-rescue personnel, at the time of the accident the ground was covered by about 10 feet of base snow and about two to three feet of fresh powder. Because of the significant avalanche danger in the days following the accident, on-site examination of the wreckage was delayed until July 19, 1997. Upon arriving at the accident site it was discovered that most of the wreckage had come to rest in a seasonal stream, and it appeared that the force of the stream flow may have moved some portions of the airframe from their original position and forced a number of small pieces of the wreckage further down the 45 degree slope. The initial impact crater was located about 10 feet north of the creek, and measured about five feet in length, three feet in width, and two feet deep. Found within the crater were both propeller blades, a section of the propeller spinner, Plexiglas, the starter, the alternator, the propeller hub, a pushrod, the bottom of the carburetor, pieces of cowling, pieces of the crankshaft, and the most-forward eight inches of the camshaft.

The largest section of the wreckage was located near the center of the creek, and about 10 feet further downhill from the crater. This section included the engine, cabin section, instrument panel, and the left wing. The front of the engine crankcase was broken open exposing the crankshaft, which was bent about 30 degrees at a point just aft of the number two cylinder crankpin. The number one cylinder hold-down studs had fractured, and the cylinder was attached to the engine only by the pushrod tubes and a portion of the baffling. All other cylinders remained attached to the crankcase, which had a secondary fracture between the number five and six cylinders. The engine remained attached to the engine mount, but had been pushed back into the firewall . The accessories were