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Mountain Waves

Ed Cesnalis

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Many, many hours.

I wish I had many, many more.


Oh, for a GoPro in the day..........


That is the Cowley Wave, off the Livingstone Range in southeastern Alberta.

It has hosted some of the most awe-inspiring and spectacular flight situations I have ever encountered, or could have even possibly imagined.


I'm sure the Minden guys know what I mean.

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How does this thread connect to FD and LSA flying? Other than the obvious high winds over mountain peaks?


You have said that you fly out of Carson City, an area where the airspace gets closed to airliners so that glider pilots can soar well into the flight levels. I have encountered lee side turbulence in your neck of the woods a few times. Knowing how to avoid the rotors as well as benefit from the lift is an everyday part of flying a light sport in the Sierra Nevada.


The photos of lenticulars and rotor clouds allow us to see what we have to visualize on most days.


Steve Fosset lost his life just a few miles from here. The Decathlon that he was flying wasn't as power to weight limited as a light sport and yet he fell victim to the lee side sink. In a light sport even more caution is required due to our limited performance.


You may think that ignorance is bliss and that these are issues for glider pilots. Encountering lee side conditions that challenge your performance and you airframe is no joke.


My FD has been upset descending through the rotor.

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How does this thread connect to FD and LSA flying? Other than the obvious high winds over mountain peaks?



Read the linked article, I know at least Adam and I use this airport. In this case a CT might have had enough climb performance to make the difference but there are plenty of waves that we cannot outperform. I never see it as a question of performance it is one of judgement instead. I flew for years in the high sierra behind 53hp.



Probable Cause #48: Mountain Waves




Airmet Tango was active over portions of California, Nevada, Utah, Colorado, Arizona and New Mexico, and warned of occasional moderate turbulence below 16,000 feet due to moderate-to-strong winds over rough terrain. Numerous pilot reports were recorded over southern California surrounding the time of the accident, and reported turbulence and downdrafts of around 500 fpm. The NTSB's report notes "performance information available in the Piper Cherokee B Owners Handbook shows that at a max gross weight of 2400 pounds and between 8000 and 10,000 feet density altitude, the airplane had a maximum climb performance of 360 to 410 feet per minute."




Probable Cause


The NTSB determined the probable cause(s) of this accident to include the pilot's "inadequate preflight planning and intentional flight into known adverse weather conditions. Contributing to this accident was the fact that it was a dark night with no moon illumination." Pilots flying over a familiar route, even at night, often neglect to obtain a weather briefing if the weather is good at their departure point. In this instance, Palm Springs was windy, with forecast winds at 10 knots and gusts to 20; an amended forecast included gusts to 25 knots. Additional information from the area's weather forecasts included the possibility of mountain wave action (see "Predicting Mountain Waves" above right) well in excess of the airplane's climb capability. Time and time again, we see accident reports where there was no record of a pre-flight weather briefing. We can't know if the simple act of requesting a weather briefing would have given this pilot information on the forecast mountain waves. However, if the pilot at least had requested a formal weather briefing, that information would have found its way into the NTSB's report. How will the NTSB's report on your accident read?

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By circumstance, I only fly in the mountains, and in certain windspeed conditions that might even be considered otherwise benign, any large massif or appropriately shaped ridge or range, even in a sea of mountains, can generate a significant local lee wave and rotor system. Identifying the clues and the potential consequences are of the utmost importance especially for a light aircraft that is easily accelerated by the air mass. These conditions can offer significant recreational possibilities (sailplane and ultralight alike), and efficiencies in transiting terrain. In some of our long, broad structural valleys, I have listened to radio chatter where goal minded pilots have been thoroughly thrashed keeping to a 'flight plan' when only a km or two away away, the going is smooth, throttled back, flying fast and smooth. I guess that Fuel Injection doesn't solve stupid.

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Clouds of a monster rotor in the lee of the Sierra Nevada near Bishop/USA. Rotorlift reached almost 30'000 ft and enabled a P38 to shut down engines and soar


Focal point of the ongoing and planned activities of the meteorological section is the Mountain Wave Project. Its ambitious goal is the global classification and analysis of mountain waves and their associated rotor bands



Leewaves (mountain waves) are atmospheric internal gravity waves and were discovered 1933 by German glider pilots above the Riesengebirge. Wind driven air parcels hitting a mountainlike obstacle are being deflected upwards and will, in a stably stratified atmosphere, return to their initial height setting up an oscillatory up-down motion. Such a wave system, which often exhibits typical phenomena as interference and wave breaking, is frequently made visible by stationary, lense shaped clouds, socalled lenticulars.






Foto: Herold/MWP rotor_p38_web.gif

Foto: Robert Symons The MWP-S10 facing spectacular dawn lenticulars. Clouds of a monster rotor in the lee of the Sierra Nevada near Bishop/USA. Rotorlift reached almost 30'000 ft and enabled a P38 to shut down engines and soar [ more]


Leewaves can reach stratospheric altitudes (=25km), where mother of pearl clouds cap the wave crests.

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