The pilot of the Cessna 182, accompanied by two passengers, was on a scenic flight near Carson City, Nevada. The airplane was climbing southwest, and approaching 9,000 feet MSL.
The pilot planned to cross a mountain saddle between 400 and 500 feet AGL. The airplane encountered a strong downdraft and the airspeed dropped to about 80 mph. The airplane stopped climbing.
It then encountered another downdraft, which resulted in an uncommanded descent. The pilot applied full power in an attempt to stop the descent, but was unsuccessful.
He maneuvered the airplane to avoid some trees before hitting the rising terrain. The airplane hit in a flat attitude, and sustained substantial damage to both wings and the tail section. There were no injuries.
The NTSB determined the probable cause as the pilot’s failure to maintain aircraft control after an encounter with downdrafts while flying over mountainous terrain.
NTSB Identification: WPR13CA231
This May 2013 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.
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On the leeward side of mountains with a known surface wind a down draft is to be expected. Not nearly enough altitude was attained before attempting the crossing. Needed to have been 1500-2000 feet above the highest peak before attempting the crossing. Nevertheless the pilot handled the situation well enough resulting in no injuries.
A good rule of thumb for pilots when crossing over mountains is to be at least half the elevation of the mountain above its highest peak, ie; 8500′ peak plan on being 4250′ above it’s peak = 12750′ msl. If your plane is unable, find an alternate route.
Don’t want to be a jerk but I fly a 150hp 2-seater around the Pacific NW (Wa, Id. Mt.) on a regular basis. I have read a fair number of “mountain flying” books (but skipped the $3-5,000 courses) and have never heard of said rule of thumb, which would prevent most GA aviation in the mountains where I live much less the high Rockies or Sierras.
We routinely fly below the mountain tops, and are taught (by other local pilots) to fly toward a gap at an oblique angle which would allow for a hasty retreat in case of any venturi effect when trying to cross a ridge line.
And yes, I have been tossed around like a leaf in mountain wave conditions. That is why experienced mountain pilots usually launch at dawn and are tying down the plane when the winds pick up later in the morning.
YMMV.
The rule, as I’ve seen it expressed, is based on the difference in MSL heights of the higher ridges and adjacent lower terrain. In E WA the Okanogan highlands have ridges at 8500` and the lower terrain is 4500-6000’. So ridge crossing over the 8500’ would be at 10,000 to 10,500’. Of course, with all the caveats of 45 d approach and avoiding mountain flying if ridgetop winds exceed X… Usually 20 kts.
As far as I’m concerned the pilot DID maintain control during the downdrafts and that’s why there were no injuries! (in contrast to the “The NTSB determined the probable cause as the pilot’s failure to maintain aircraft control after an encounter with downdrafts while flying over mountainous terrain.” in the report.
Colorado Pilots Association mountain flying class guidelines are 1,500 feet clearance over passes. I wonder if the pilot had taken any mountain flying course. 400 ft is not nearly enough.
I fly that route often and wouldn’t consider crossing the mountains with less than a couple thousand feet clearance. Particularly when the wind is coming from the West causing the expected downdrafts on the Carson side.