BOISE, ID, USA
N7583P
Piper PA-24-250
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 crushed between the engine and the firewall and were not accessible at the accident site. All spark plugs were securely in their mounting holes, and all ignition wires were still attached to the appropriate plug. All spark plugs, (except those in cylinder number five, which could not be removed) showed a consistently gray appearance, and showed fresh surface corrosion of their metal surfaces. Electrode wear was not excessive, and the rate of wear was consistent among all cylinders. Both propeller blades had separated from the hub, and both exhibited leading edge impact damage. One blade had a one inch deep gouge in its leading edge about eight inches from its tip, and the other had a one-half inch deep gouge in its leading edge about three inches from its tip. The blade with the gouge three inches from the tip showed about 30 to 40 degrees of longitudinal twisting, and was curved backwards about 40 degrees along the outboard two-thirds of its span too. The other blade was bent backwards about 10 degrees along the outboard three-quarters of its span. The vacuum pump, which had received external impact damage, was disassembled and revealed a fractured rotor with all vanes in place and undamaged. Except for reddish-brown stains created from oxidation of the metal center-post, there was no sign of contamination within the pump or its lines, and there was no excessive wear apparent on either the rotor or the vanes. The attitude indicator was disassembled and no contamination was found within the gyro casing or its air intake/exhaust system, nor was there any evidence of damage to the gyro rotor. Most of the cabin section was together at one location, but it had been severely crushed, torn and deformed by the impact. The instrument panel had been destroyed, and most of the instruments had been thrown from the wreckage. The seats had separated from their anchor points and were severely distorted. The left wing was still partially attached to the fuselage, and showed rearward crushing along its entire span. Although the flap was still attached, the aileron had separated and was found further along the impact track. The right wing had separated from the fuselage at its root, and the inboard section was found further along the impact track near the empennage. There was rearward crushing of the inboard section of the right wing, but the outboard half of the wing and its associated aileron were not located at the accident site. Because of the extent of the damage at the location were the inboard and outboard sections of the wing had separated, it could not be determined if the outboard section of the wing had come off in flight, or whether it had slid down the steep snow-covered slope and was carried away by the river below. The aileron, stabilator, and rudder cable cables had failed in a mode consistent with tensile overload, but due to the extent of damage to both the fuselage and wings, pre-impact control continuity could not be confirmed. The empennage was found about 30 feet below the impact crater along the north side of the stream. The anti-servo tab was still attached to the stabilator, and the rudder was still attached to the vertical fin, but the entire empennage showed extensive wrinkling, twisting, bending and crushing. Further inspection of the wreckage after removal to the aircraft salvage yard did not reveal any evidence of pre-impact discrepancies with the airframe, flight control system, or engine. ADDITIONAL DATA AND INFORMATION The aircraft wreckage was released to Specialty Aircraft at Redmond, Oregon, on September 16, 1997. The FAA's Toxicology and Accident Research Laboratory completed a forensic toxicology examination on the pilot, and no drugs were detected in the muscle. A volatiles analysis was completed, and Ethanol and N-Butanol was detected in the Brain and Muscle. In addition Methanol, N-Propanol, Isobutanol were detected in the brain, and Acetaldehyde was detected in the muscle. It was noted in the report that "The ethanol found in this case may be the result of postmortem ethanol production." No tests for Carbon Monoxide or Cyanide were performed due to a lack of suitable specimens. An autopsy was performed by Frank A. Roberts M.D., and the cause of death was listed as massive total body trauma.
the accumulation of airframe ice on the aircraft, and the pilot's delayed remedial action after intentionally flying into forecast adverse weather conditions. The adverse weather (icing) conditions were related factors.
Source: NTSB Aviation Accident Database
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