TYONEK, AK, USA
N5297U
Cessna 206
The pilot and five passengers departed eastbound from a rural airstrip for a cross-country flight across high mountainous terrain. He had flown along the planned route of flight numerous times in the past and obtained pilot reports of weather conditions in several mountain passes that traversed the mountain range along the planned route. The weather reports included wind speeds of 40 knots with turbulence. An area forecast included AIRMETs for mountain obscuration, turbulence in all mountain passes, and icing conditions. The pilot said he was aware of the potential for turbulence over the mountains and climbed the airplane to 13,500 feet. When the flight approached the lee side of the pilot's planned crossing point over the mountains, the airplane encountered severe downdrafts. The pilot applied full power, but the airplane continued to descend toward blowing snow along the mountain ridge. The pilot said he had no alternative but to land into a snow bank. The airplane collided with snow covered terrain at 10,500 feet msl. The airplane's belly mounted cargo pod, and the landing gear were torn off the fuselage.
On May 27, 1998, about 1400 Alaska daylight time, a wheel equipped Cessna 206 airplane, N5297U, sustained substantial damage during a collision with mountainous terrain, about 40 miles west of Tyonek, Alaska. The airplane was being operated as a visual flight rules (VFR) cross-country personal flight under Title 14 CFR Part 91, when the accident occurred. The airplane was registered to William Merrill Jr., Anchorage, Alaska, and operated by the pilot. The certificated commercial pilot, and four passengers were not injured. One passenger received minor injuries. Visual meteorological conditions prevailed. No flight plan was filed by the pilot. The flight originated at the Lime Village Airport, Lime Village, Alaska, about 1200. At 1224:17, the pilot contacted the Kenai, Alaska, Automated Flight Service Station (AFSS) via aircraft radio. The pilot requested pilot reports of weather conditions for Merrill Pass and Lake Clark Pass, and the weather conditions at Anchorage International Airport, and Merrill Field, Anchorage. The Kenai AFSS specialist provided weather information that included a report of continuous moderate to occasional severe turbulence in the west end of Lake Clark Pass. The specialist also advised of a pilot report in the area of Sparrevohn Long Range Radar Station (16 miles south of Lime Village). That report indicated a south wind at 40 knots with occasional light turbulence at 5,500 feet msl. The specialist also provided a report of winds along Turnagain Arm (7 miles south of Anchorage) that indicated wind from the east at 40 knots. At 1227:23, the pilot stated, "97U roger, ah you got a pretty stiff gradient between here and there, ah evidently where the winds are coming from, ah thanks ah lot, I'll try and give you a report on Merrill Pass". During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on May 28, 1998, at 1000, the pilot reported he began flying earlier in the day with a planned destination of Anchorage. He departed Stony River, Alaska, and flew to Sleetmute, Alaska, and then to Lime Village. After departure from Lime Village, the pilot indicated he usually crossed the Tordrillo Mountains via a 9,000 foot high pass, located between Mt. Torbert, and Mt. Gerdine. The usual time en route for the trip to Anchorage is 2 hours. After flying for 2 hours, the flight had only progressed to the mountain pass, which is about 88 miles east of Lime Village. The pilot stated he anticipated strong winds and turbulence over the mountains, and climbed the airplane to between 13,000, and 13,500 feet msl. As the flight approached the mountain pass, the airplane suddenly began to descend. The vertical speed indicator was indicating a 2,000 feet per minute rate of descent, but the pilot said the airplane dropped over 3,000 feet in less than 1 minute. The pilot reported he added full power, and raised the nose of the airplane. The airspeed indicator was between 80 to 90 knots. The airplane continued to descend into blowing snow on the lee side of a mountain ridge. The pilot said he had no alternative but to land into a snow bank. The airplane collided with snow covered terrain at 10,500 feet msl, on the side of Mt. Torbert. The airplane's belly mounted cargo pod, and the landing gear were torn off the fuselage. An area forecast for the southern half of Alaska, except southeast Alaska, issued on May 27, 1998, at 1145, was reporting in part: "Cook inlet and Susitna Valley, valid until 0000; AIRMET, mountain obscuration - mountains temporarily obscured in clouds and precipitation, no change. Clouds conditions, 3,000 feet scattered, 6,000 feet broken, layered above, tops at 25,000 feet. Temporarily, 3,000 feet broken, 6,000 feet overcast, visibility 5 statute miles in light rain. Along the Alaska range, temporarily 2,000 feet broken, 5,000 feet overcast, visibility 3 statute miles in light rain and mist. Through passes, surface winds from the east to southeast at 20 knots, gusts to 30 knots. Outlook valid from May 28, 1998, at 0000 to 1800, VFR. Passes, all passes turbulent. Lake Clark, Merrill, Rainy, and Portage Pass, marginal VFR ceilings in rain. Windy, VFR. Turbulence, AIRMET for turbulence. Temporary moderate turbulence below 8,000 feet, no change. Icing and Freezing level, AIRMET for icing. Temporary moderate rime icing in clouds, 5,000 feet to 10,000 feet. Freezing level, 5,000 feet. At 1454, a military AWAC airplane monitored a "mayday" call from the accident airplane. Search and rescue personnel reached the accident site about 2230.
The pilot's continued flight into adverse weather conditions, and his inadequate in-flight planning/decision. Factors in the accident were weather conditions consisting of a mountain wave, and downdrafts.
Source: NTSB Aviation Accident Database
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