ANC17FA004

The airplane's collision with mountainous terrain while operating in an area of reduced visibility and icing conditions. Contributing to the accident was the pilot's inadequate preflight planning, which would have identified deteriorating weather conditions along the planned route of flight.

The commercial pilot was conducting a cross-country flight to a family residence in the turbine-powered, single-engine airplane. The pilot was familiar with the route, which traversed a mountain pass and remote terrain. Before departing on the flight, the pilot communicated with a family member at the residence via text messages and was aware the weather was windy but that the mountain tops were clear. There was no record of the pilot obtaining a preflight weather briefing from an official, access-controlled source, and the pilot indicated to a friend before departure that he had not accessed weather cameras. Weather forecast products that were available to the pilot revealed possible turbulence at low altitudes and icing at altitudes above 12,000 ft along the route of flight, and weather cameras along the planned route and near the destination would have indicated deteriorating visibility in snow showers and mountain obscuration starting about 1.5 hours before departure. The airplane departed and proceeded toward the destination; radar data correlated to the accident flight indicated that the airplane climbed from 4,600 ft to 14,700 ft before turning west over the mountains. Text messages that the pilot sent during the initial climb revealed that the mountain pass he planned to fly through was obscured, and he intended to climb over the mountains and descend through holes in the clouds as he neared the destination. Radar data also indicated that the airplane operated above 12,500 ft mean sea level (msl) for about 30 minutes, and above 14,000 msl for an additional 14 minutes before entering a gradual descent during the last approximate 20 minutes of flight. Review of weather information indicated that cloud layers over the accident area increased during the 30 minutes before the accident, and it is likely that the airplane was operating in icing conditions, although it was not certified for flight in such conditions, which may have resulted in structural or induction icing and an uncontrolled loss of altitude. The airplane wreckage came to rest on the steep face of a snow-covered mountain in a slight nose-down, level attitude. The empennage was intact, the right wing was completely separated, and the forward fuselage and cockpit were partially separated and displaced from the airframe with significant crush damage, indicative of impact with terrain during forward flight. There was no indication that the airplane was equipped with supplemental oxygen; pilots are required to use oxygen when operating at altitudes above 12,500 ft for more than 30 minutes, and anytime at altitudes above 14,000 ft. It could not be determined if, or to what extent, the pilot may have experienced symptoms of hypoxia that would have affected his decision-making. The airplane wreckage was not recovered or examined due to hazardous terrain and environmental conditions, and the reason for the impact with terrain could not be determined; however, it is likely that deteriorating enroute weather and icing conditions contributed to the outcome of the accident.

There was no record of the pilot receiving a weather briefing from an FAA Flight Service Station or from the Direct Users Access Terminal (DUAT) system. It could not be determined what, if any, sources of weather information the pilot may have accessed before the flight. The National Weather Service (NWS) Alaska Aviation Weather Unit's (AAWU) Alaska Surface Forecast Chart valid for 1600 on the day of the accident depicted an occluded frontal system with a cold front extending southwest of the accident site. A large area of expected light continuous rain was depicted along the frontal system. The chart also depicted an increasing pressure gradient with tight packing of the isobars over western and southwest Alaska. The accident site was depicted ahead of the expected precipitation area and was within an area of potential increasing southeasterly winds; however, no significant weather was depicted between Anchorage and Port Alsworth. The NWS AAWU Flying Weather Graphic Forecast charts issued for 1200 to 1800 and 1800 to 2400 showed VFR conditions for the planned and actual flight routes. The NWS AAWU icing and turbulence forecast charts indicated that the accident site was on the border between an area of predicted occasional to continuous moderate turbulence below 4,000 ft and isolated severe turbulence below 6,000 ft. The icing forecast chart for 1800 indicated that the accident site was under an area of forecast isolated moderate icing from 12,000 ft to FL200. The nearest weather observation for the intended destination that would have been available to the pilot before departure was Port Alsworth Airport (PALJ). The 1650 observation reported wind from 060° at 10 knots, visibility 30 miles, an overcast ceiling at 10,000 ft, temperature 10°C, and dew point temperature 4°C. The official weather observation nearest to the accident site was Sparrevohn Airport (PASV), about 60 nm west at an elevation of 1,565 ft. The 1755 automated observation reported wind from 140° at 20 knots gusting to 41 knots, visibility 10 miles, an overcast ceiling at 8,500 ft agl, temperature 9°C, dew point 1°C, altimeter 29.57 inches of mercury. A review of the MesoWest database from the University of Utah revealed remote automated weather system (RAWS) data from Stoney (STNA2), located about 13 miles west-southwest of the accident site at an elevation of 1,226 ft. The station reported a north wind at 6 knots with a peak gust of 17 knots, temperature 41°F with a temperature-dew point spread of 5°F and relative humidity 83%, suggesting a high probability of low clouds and restricted visibility. A review of archived FAA weather camera images at Lake Clark Pass East, Lake Clark Pass RCO, Merrill Pass Low and Merrill Pass High all indicated deteriorating weather starting about 1530 and visibilities of 1 mile or less in snow showers with mountain terrain obscured by 1600. The Lake Clark Pass West northeast view, which was closest to the planned destination, revealed that, at 1838, the clouds were above the highest terrain and visibility was unrestricted, which was corroborated by the family member's observations provided to the pilot. The FAA weather camera website states that the camera weather images are supplementary products and may only be used to improve situational awareness. The closest upper air sounding was from the NWS Anchorage (PANC) Forecast Office, about 105 miles east of the accident site. A review of the 1600 sounding indicated a high potential for moderate rime-type icing conditions at 9,330 ft within the shallow layer of broken altostratus type clouds. The air sounding wind profile indicated that, at the accident airplane's cruising altitudes between 9,500 ft and 10,500 ft, the wind was from 210° at 20 knots, with a temperature of -10°C. At 14,500 ft, the highest altitude the airplane operated at during the flight, the wind was from 235° at 23 knots with a temperature of -11°C. The primary freezing level aloft was about 4,880 ft. Archived satellite data was obtained and processed for 1800 and 1830 over the accident area. Infrared image for 1830 depicted the accident site under multiple layers of clouds with temperatures corresponding to cloud tops near 30,000 ft or high, cirrostratus-type clouds. The closest Weather Surveillance Radar-1988, Doppler (WSR-88D) was NWS Anchorage/Kenai (PAHG), located 65 miles east of the accident site showed echoes consistent with snow showers. The radar product's depiction of the large area of echoes and the satellite imagery confirm that a layer of altostratus to nimbostratus-type clouds were over the route and over the accident site during the period, with likely snow showers, associated with lower ceilings and visibilities over the route of flight. The United States Naval Observatory website lists the following astronomical data for October 28, 2016: sunset 1807, end of civil twilight 1853, moonset 1807. A weather study is available in the public docket. The pilot, age 55, held a commercial pilot certificate with ratings for airplane single-engine land, single-engine sea, and instrument airplane. He held a second-class FAA medical certificate issued on April 1, 2016, with a limitation that he must have available glasses for near vision. On the application for that medical certificate, the pilot reported 6,400 total hours of flight experience and 43 flight hours in the previous 6 months. No personal flight records were located for the pilot. The high-wing, conventional-gear, turbine-powered airplane was manufactured in 1975 by Fairchild Heli-Porter under the design authority of Pilatus Aircraft Limited of Stans, Switzerland. According to FAA airworthiness records, the airplane was equipped with a 575-shaft horsepower Garrett AiResearch TPE331-1-151K turbine engine under FAA supplemental type certificate (STC) SA5959NM. The propeller was a three-bladed Hartzell metal propeller. The airplane was equipped with an Artex ELT model ME406 and a radar altimeter. The airplane was also equipped with an internal 250-gallon fuel transport tank. There was no evidence that the airplane was equipped with supplemental oxygen. According to a friend of the pilot who was a mechanic, the airplane was in very good condition and he occasionally helped the pilot with maintenance. He stated that, a few weeks before the accident, he assisted the pilot with troubleshooting an electrical problem that was preventing the engine from starting. He repaired a terminal wire and the airplane was returned to service. According to the friend, the engine, airframe, and propeller logbooks were on the airplane at the time of the accident. The logbooks were not located. The remote accident site was located in steep, mountainous, snow-covered terrain within the Neacola mountains of the Alaska Range, with a peak of about 8,336 ft in the near vicinity. The wreckage was located about 6 miles south of Merrill Pass west and 14 miles northeast of Lake Telaquana within the Lake Clark National Park and Preserve. The airplane initially came to rest on the south side of an east-west ridge of a mountain bowl. When the rescue crew arrived, the airplane was mostly covered by 3 ft of snow and was in a slightly nose down, level attitude oriented on an easterly heading across the mountain face at an elevation of about 6,500 ft. A review of photographs provided by AKRCC revealed that the forward fuselage and cockpit had been torn away and partially separated from the aft section forward of the wing roots. The forward fuselage and engine were displaced aft and to the right and displayed significant crush damage. The right wing was missing, and the left wing was partially attached and displaced downward. The empennage was intact, and the rudder was fractured about 3 ft from the top. Jet A fuel was present on recovered clothing and manuals. A Garmin GPSMAP 396 and a personal electronic device were recovered by the rescue and recovery crew.