ANC23LA065 · Beech B36TC

The instrument-rated pilot and passenger departed on a cross-country flight over mountainous terrain. The airplane departed an airstrip near the pilot’s residence about 0850 with a planned stop in Ketchikan, Alaska, before continuing to Washington state. The pilot established contact with an Anchorage Air Route Traffic Control Center controller when the flight was at 12,000 ft mean sea level (msl) about 25 minutes after departure. The controller advised the pilot he would need to climb to a higher altitude due to terrain and weather. The pilot responded that the airplane was turbocharged and that a higher altitude would not be a problem. The controller instructed the pilot to climb to 14,000 ft and advised him that, due to the remoteness and terrain, he might lose contact with the controller and issued backup frequencies. At 0953 the controller approved the pilot’s request to climb to 15,000 ft; there was no further communication from the pilot. The next day, a search and rescue crew located the wreckage, but terrain and poor weather conditions precluded reaching the site. The National Park Service overflew and photographed the site and concluded that, due to the unique challenges posed by the accident location, neither the occupants nor the wreckage would be recovered. The pilot obtained three preflight weather self-briefings from ForeFlight with a planned cruising altitude of 13,000 ft. Between the second and final briefing, the pilot requested the maximum icing severity image, icing potential for 11,000 ft and 12-hour icing forecast, and the 18,000 ft winds aloft forecast. Archived versions of the icing product viewed by the pilot were not available in the ForeFlight database or available from the NWS and the products the pilot requested were only available for the contiguous United States and were not created for the Alaska region. Weather soundings, forecasts, and experimental weather images depicted a greater than 70% probability of moderate to heavy icing above 12,000 ft through 15,000 ft. Data also indicated that the icing threat increased as the accident airplane climbed from 14,000 ft to 15,000 ft. Based on the weather data, the airplane likely encountered supercooled large droplet (SLD) conditions during the last minutes of the flight that degraded the airplane’s performance and resulted in a loss of control. According to the airplane pilot’s operating handbook (POH), flight into known icing conditions was prohibited. The National Weather Service (NWS) had issued advisories for instrument flight rules (IFR) and mountain obscuration conditions over the area; low clouds and precipitation were also present. The NWS area forecast and Alaska Aviation Weather Unit (AAWU) graphic icing forecasts were for isolated moderate icing in clouds between 17,000 ft and 22,000 ft, with the freezing level identified at 14,000 ft. However, the NWS underestimated the area and intensity of the icing conditions over the region and did not have in-flight advisories in effect around the time of the accident for all altitudes affected by icing. The pilot completed his instrument rating in the contiguous United States about two months before the accident, where the graphic map display of current and forecast icing products would have been available to him during his training. It’s likely he was looking for these images in ForeFlight, but they were not available for Alaska. Although the icing information was available to the pilot in a vertical cross-section chart, the graphic map that displayed areas of icing along his route of flight would have been familiar to him and visually consistent with other popular weather mapping products. Access to the icing information in this format would have given him the best opportunity to select a different route. Additionally, although the graphic icing information in Alaska was not available to the public or pilots, it was available to Alaska Flight Service weather briefers; however, the pilot did not obtain a formal weather briefing. Due to the expansive mountainous terrain in the area of the accident, there were no options for the pilot to exit icing conditions once he entered them. The pilot was unable to access icing products that were familiar to him, his airplane was not equipped for flight in icing conditions, yet he selected the riskier route over the mountains. After inadvertent flight into icing conditions, he did not notify air traffic control of his situation or initiate a 180° turn to exit icing conditions.

Verbatim NTSB analysis and probable cause from the NTSB dataset