Darling Downs Aero Club
Est. 1946
As the windy winter westerlies continue knocking at our door, now seems like the perfect time to refresh our awareness of the regional hazard of Mountain Waves. These are a hazardous met phenomena which should be at the back of every pilot’s mind when flying around the Great Dividing Range, particular this time of year.
What makes mountain waves so hazardous to aircraft, particularly to us Cessna and Piper pilots? It is the turbulence and strong wind shear encountered on the lee side of the mountain that can push aircraft into the hills, even when our normally trusty steed is configured for its best climb performance. Added to this is the at times stealthy presence of the mountain waves in the absence of any ‘telltale’ lenticular cloud formation.
With this in mind, it is important to maintain vigilance when flying in certain atmospheric conditions more conducive to the formation of mountain waves. But what are these conditions?
· Significant mountain range that is more than 1000ft higher than the surrounding terrain (eg: Great Dividing Range)
· Wind speed at mountain top >25kts (winter westerlies) crossing the mountain range at close to 90degrees.
· Inversion or stable layer at top of system
The mountain waves are present on the lee side of the range and can persist for many miles downwind. If you must cross the range when mountain waves are potentially present, choose to fly above the inversion layer and avoid crossing the mountain ‘head on’. Instead, aim to cross the range from closer to a 45 degree angle, thus minimising the heading change required in the event of unfavourable conditions. If unforecast mountain waves are found to be present, you can make a Special Air Report (airep special) to ATC to alert other pilots in the area. An air met can be issued in addition to MTW on the GAF. However, despite all of the best forecasting, it is still up to us as pilots to assess the weather conditions; and stay vigilant!
You can read more information about Mountain Waves here.
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