HUNTSVILLE, UT, USA
N54TM
Piper PA-28-161
The flight instructor and his student were from Fort Worth, Texas, and they were crossing a mountain ridge eastbound at 9,500 feet msl when the flight instructor reported that they 'encountered a serious downdraft.' He immediately began a 180 degree turn and then reversed direction again back eastbound. The flight instructor stated that the 'airplane was descending about 2,500 feet per minute with full power.' The student stated that 'just as we hit some trees, I remember hearing the stall horn.' The forecast wind aloft was approximately 10 knots at 9,000 feet msl. The density altitude for 10,000 feet was calculated to have been 13,061 feet. Using the airplane's manufacturer Climb Performance charts, N54TM had approximately 210 feet per minute climb capability. The degree of bank that the flight instructor utilized for his turns was not documented, but, the book 'Flight Theory For Pilots' states that as the turning bank angle increases, the energy demands to maintain level flight asymptotically increases. The flight instructor reported that he acquired most of his flight training in Colorado Springs, Colorado, before moving to Fort Worth, Texas.
On August 8, 1998, approximately 1630 mountain daylight time, a Piper PA-28-161, N54TM, was destroyed following impact with mountainous terrain near Huntsville, Utah. The commercially certificated flight instructor and his student were seriously injured. The airplane was being operated by a private individual under Title 14 CFR Part 91. Visual meteorological conditions prevailed for the cross-country instructional flight which originated from Tremonton, Utah, approximately 45 minutes before the accident. No flight plan had been filed. The flight instructor said that he and his student were from Fort Worth, Texas, and they were returning from a trip to visit friends in Washington state. The student reported that they had climbed between 9,500 and 10,000 feet msl to cross a mountain ridge. The flight instructor said that after crossing the ridge "I encountered a serious downdraft" and he immediately began a 180 degree turn to go back to smooth air. He further stated "halfway through the turn I realized that I could not make it back over the ridgeline" and he turned the airplane back towards the east once again. The flight instructor stated that the "airplane was descending about 2,500 feet per minute with full power." The student stated that "just as we hit some trees, I remember hearing the stall horn." The airplane impacted the terrain at 7,800 feet. The National Weather Service forecast winds aloft between 1200 and 1800 were 15 knots reducing to 7 knots at 9,000 feet. At 12,000 feet, the winds were forecast to be 16 knots, reducing to 11 knots. The altimeter for Salt Lake City International Airport at 1653 was 30.05 inches of mercury and the surface temperature was 33 degrees Celsius. Using the standard adiabatic lapse rate, the respective temperatures at 9,500 and 10,000 feet msl would have been 23 and 22 degrees Celsius, respectively. Using these figures, the density altitudes for 9,500 and 10,000 feet would have been 12,562 feet and 13,061 feet, respectively. Using the airplane's manufacturer Climb Performance charts which are published in the Pilot Operating Handbook, the approximately climb capability of N54TM at 10,000 feet msl, under the above weather conditions, was 210 feet per minute. The flight instructor reported that he performed two turns in an attempt to find smooth air. In the book "Flight Theory For Pilots" by Charles Dolo (see attached documentation), the author states: "In turning flight the airplane is not in a state of equilibrium, since there must be an unbalanced force to accelerate the plane into the turn." The degree of bank that the flight instructor utilized for these turns was not documented, but as the attached document brings out, as the turning bank angle increases from straight and level flight, the energy demands to maintain level flight asymptotically increases. The flight instructor reported to the Investigator-In-Charge that he had acquired most of his flight training in Colorado Springs, Colorado, before moving to Fort Worth, Texas.
The flight instructor's failure to ensure adequate altitude/clearance with terrain, resulting in an encounter with a downdraft, loss of airspeed, onset of a stall/mush, and collision with high terrain.. Contributing factors were high density altitude, downdrafts, mountainous terrain, and trees.
Source: NTSB Aviation Accident Database
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