The pilot reported that, while flying in mountainous terrain around 9,500′ mean sea level (700′ to 1,200′ above the ground), the Cessna 182 encountered a downdraft.
He added that he immediately turned away from the mountainside in a right turn, added full power, selected 10º of flaps, and pitched the nose up to maintain the airplane’s maximum angle-of-climb airspeed (Vx).
Subsequently, the plane was unable to climb, and it hit wooded, snow-covered terrain along the mountainside near Mackay, Idaho.
The fuselage and both wings sustained substantial damage.
The pilot reported that there were no preaccident mechanical malfunctions or failures with the airplane that would have precluded normal operation.
The calculated density altitude near the flightpath was about 10,339′. According to the FAA Koch Chart, the airplane would have experienced a 50% decrease to the normal climb rate. The high-density altitude conditions likely contributed to the airplane’s inability to establish a climb.
Probable cause: The pilot’s decision to maneuver the airplane over mountainous terrain in high-density altitude conditions, which resulted in the airplane’s inability to maintain altitude or establish a climb.
NTSB Identification: GAA17CA202
This March 2017 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.
Classic mountain flying error, trying to raise the nose to maintain altitude or reduce descent in a downdraft. Raising the nose increases AOA, increases drag (and this pilot added flaps!) and increases the amount of time you spend in the down draft. Remember the TSD problem in pilot training that demonstrates why you can’t make up time lost in a head wind by turning around to make it a tail wind? Correct response is to lower the nose and fly out of it downslope. The downdraft doesn’t have a vertical component when it gets close to the ground. It spreads out and follows the slope downhill so it won’t blow you into the ground. You may get a close look at the trees but you won’t hit them unless you stall the wing or give away so much performance that the L/D ratio is negative.
Engine Power and Engine Power Rating
Engine power developing thrust is what sustains the aircraft in level and climbing flight. When maintaining a constant indicated-airspeed, constant altitude, wings level flight, the engine power is providing the sustaining-thrust.
At any altitude or attitude, it requires a constant mass-of-the-air displacement with its constant encountering pressure for the selected indicated-airspeed condition.
Manufacturer rating of engines are determined with the use of sea-level standard conditions. A 110-horsepower-rated engine can produce the 110 horsepower only at sea level on a standard day. The typical aircraft with this 110-horsepower engine in the standard conditions can produce approximately 460 pounds of thrust.
In the lower atmosphere there is an approximate linear pressure reduction as altitude increases, and for this reason, engine power gradually decreases during climb. As an example, if your engine/propeller, at full throttle, produces 460 pounds of thrust at sea level, but will produce only its sustaining thrust of 160 pounds at slightly below 12,000 feet, this is a 300-pound reduction of thrust available.
In this example, there is a 25-pound reduction of thrust for each 1,000 feet of increased altitude. At 5,000 feet, you can expect to have 335 pounds of thrust available but only 175 pounds of excess thrust for maneuvering. At 10,000 feet, you will have 210 pounds of thrust available but only 50 pounds of excess thrust for maneuvering. At 12,000 feet, there will be only 160 pounds of thrust, leaving no thrust available for maneuvering without descent for adding gravity component-thrust.
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I have seen some try to challenge the Sierras in summer conditions in weight shift kites, Cessna 172 and 182s and other small planes. Pure poker playing. Why do something on the edges in aviation? Stay inside your limits and live.