If you plan on doing any flying in a high altitude mountainous areas, Bill Schroeder, a Certified Flight Instructor who has been flying in the Lake Tahoe/Sierra Nevada Mountain region for more than 25 years, has written a very lengthy and must read article for General Aviation News about how to escape from a downdraft.
Bill began by relating a hypothetical downdraft situation in the Sierra Nevada mountains that unfortunately is an all to common occurrence – especially for pilots not accustomed to high altitude mountain flying. Bill then wrote about some tried and true methods for heading into the wind while flying over ridges or a series of ridges.
For starters, Bill noted that when a pilot is within a quarter to a half mile from the ridge, he or she should always approach the ridge at a 45° angle. He noted that it is dangerous to fly directly towards a ridge’s lee side when the wind exceeds 10 knots and you are slightly above, level or below the ridgeline.
Bill also pointed out that a steady wind of 10 knots that is being funneled through a mountain pass or any uneven surface can greatly increase in speed and this phenomena is known as the “venturi effect.” In fact, wind speeds may actually double and or even in a mountainous environment.
Bill then described in detail how to safely fly over a mountain ridge and then he noted that downdrafts come in different forms. For example: Some downdraft are smooth and you may not even realize that you are caught up in one unless you are keeping a close eye on the vertical speed indicator. Hence, you should always watch your vertical speed indicator while flying in mountainous areas.
On the other hand, some downdrafts may cause a sudden and severe jolt that is then followed by a lull and more jolts – which can come from all directions. This could make your aircraft difficult to control. However, its also important to not over-control the aircraft and accept altitude loss while attempting to fly at a safe altitude.
At the end of the article, Bill pointed out that most downdraft related accidents are caused by a pilot’s concern about altitude loss instead of trying to escape from the ridge that is actually causing the downdraft and altitude loss in the first place. Hence, Bill’s entire lengthy article about downdrafts is a must read if you intend to do any high altitude flying over mountains.
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