Aviation Accident Summaries

Aviation Accident Summary DEN99LA030

ROLLINSVILLE, CO, USA

Aircraft #1

N8112S

Piper PA-28-181

Analysis

The pilot obtained a weather briefing for a cross-country flight from Boulder to Steamboat Springs which called for a SIGMET for severe turbulence due to strong winds in the vicinity of the mountains, and AIRMETS for mountain obscuration and moderate to severe turbulence. The winds aloft were forecasted to be 310 degrees at 48 knots (9,000 feet), 320 degrees at 56 knots (12,000 feet), and 310 degrees at 66 knots (18,000 feet). The pilot was going to rent a car, then later changed his mind. While en route, he encountered low visibility and obscuration due to blowing snow and mountain obscuration. He decided to turn around and descend, and was then 'caught in a powerful smooth air downdraft.' The aircraft impacted the ground and the right wing and left landing gear were sheered off. According to a witness, weather conditions at the time of the accident included 'snow, blowing snow, limited visibility, and winds gusting to approximately 40 mph... A stormy day to be sure.' At the time of the accident, the pilot had 18 years of flight experience, the majority and most recent of which was conducted in California. He was unfamiliar with the geographic location and with mountain flying.

Factual Information

On December 30, 1998, approximately 1155 mountain standard time, a Piper PA-28-181, N8112S, owned and operated by the pilot, was substantially damaged after colliding with terrain while maneuvering near Rollinsville, Colorado. The private pilot and his two passengers received minor injuries. The personal flight was being conducted under Title 14 CFR Part 91, and no flight plan had been filed. The flight originated from Boulder Municipal Airport, Boulder, Colorado, approximately 45 minutes before the accident, with an intended destination of Steamboat Springs/Bob Adams Field Airport, Steamboat Springs, Colorado. Visual meteorological conditions prevailed at the accident site. At 1330 on the day before the accident, the pilot obtained a weather briefing for a cross-country flight from Boulder to Steamboat Springs. He loaded the aircraft with skiing equipment and luggage, and departed Boulder at approximately 1600. He stated that the "flight was intended as a local flight for familiarization with terrain, flying conditions and wind actions... Crossing would have been attempted if conditions had been adequate." However, "Clouds prohibited any attempts to cross the mountains to Steamboat Springs," and he returned to Boulder. At 1000 on the morning of the accident, the pilot obtained another weather briefing from the Denver Automated Flight Service Station that called for visual meteorological conditions. There was a SIGMET (Significant Meteorological Information) in effect for moderate to occasionally severe turbulence below 16,000 feet due to strong, gusty low to mid-level winds in the vicinity of the mountains, and an AIRMET (Airman's Meteorological Information) in effect for mountain obscuration and moderate to severe turbulence. In addition, there were numerous PIREPS (pilot reports) regarding moderate turbulence. Between the time period of 1000 to 1400 mst, the forecasted winds aloft were reported to be 310 degrees at 48 knots (9,000 feet); 320 degrees at 56 knots (12,000 feet); and 310 degrees at 66 knots (18,000 feet). At 1020, the pilot called the Steamboat Springs airport and asked an airport employee what the weather conditions were. He was told the conditions were an estimated ceiling of 3,500 feet, "good" visibility and "reasonable" winds. The employee then asked the pilot if he was IFR capable, to which he replied, "yes, but I would not like to go through the clouds at this high altitude with the small aircraft due to lack of oxygen, no deicing equipment, and insufficient performance reserve." The employee then suggested that he attempt to fly through the Corona Pass on the 269 degree radial off of the Denver VOR. According to the pilot, he made the decision not to fly due to the strong headwinds, and instead was going to rent a car. Later, he changed his mind. He decided to "make a local flight in order to become familiar with the area to the south on the foothills, identify Corona Pass and look for the cloud cover that was not visible from Boulder." He stated that "if suitable conditions were found [he] would proceed, otherwise [he] would return and take the car." While en route approximately 40 miles west of Boulder, he encountered low visibility and obscuration due to blowing snow. The mountains were obscured, and he decided to turn around and descend in order to identify the pass. Upon reaching a lower altitude, the visibility was reduced to 5 to 8 miles with snow flurries. He began to turn away from the ridge and at that time, he was "caught in a powerful smooth air downdraft." The pilot estimated the aircraft's ground speed to be 40 knots when he "aimed between the middle of the tops of two high trees" along rising terrain. The aircraft impacted the ground at the 10,600 foot elevation of Rollins Pass. The right wing and left landing gear were sheered off, and the stabilator was bent. The airplane came to rest on its right side with a 150-foot path of sheared tree tops leading up to the aircraft. A witness, who was cross-country skiing in the area at the time of the accident, heard the aircraft's engine and observed the airplane pass overhead approximately 100 feet above the trees. He heard the engine stop, followed by the sound of impact a half a second later. He stated that weather conditions at the time of the accident included "snow, blowing snow, limited visibility, and winds gusting to approximately 40 mph... A stormy day to be sure." At the time of the accident, the pilot had 18 years of flight experience, the majority and most recent of which had been conducted in California. He stated that he was unfamiliar with the geographic area and mountain flying. According to a pilot with 13 years of mountain flying experience, "most experienced pilots avoid mountain flying when winds reach more than 30 knots."

Probable Cause and Findings

The pilot's inadequate decision to continue flight into deteriorating weather conditions, that included a downdraft which resulted in a loss of control, and collision with terrain. Contributing factors were the pilot's lack of familiarity with the terrain, high winds, obscuration and mountainous terrain.

 

Source: NTSB Aviation Accident Database

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