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• Thunderstorm Turbulence.
The storm cloud is only the visible portion of a turbulent system. Up- drafts and downdrafts often extend outside of the storm, with severe tur- bulence possible as much as 15 to 30 miles downwind and 5,000 feet above the storm.
It’s Thunderstorm Season
While turbulence is normal and hap- pens often, it can be dangerous and each season has its weather challenges. Spring has fast-moving fronts and high winds causing severe squall lines. Summer has thunderstorms and tropical storms. Autumn is usually the quietest season. Winter has higher winds, blizzards and more frequent clear air turbulence. Visible moisture (cloud) is typically in- dicative of a bumpy ride, but often, air movement that causes bumps is invis- ible and occurs unexpectedly. In April, the Jetstream and its associated clear air turbulence have shifted north into Canada, usurped by convective turbu- lence that peaks April through August across North America.
From April 16 through June 15 of 2018, data from my carriers TAPS equipped aircraft (Turbulence Auto PIREP System) reported that there were 200 incidents of moderate or severe turbulence. Ap- proximately 76 percent of the moderate or greater turbulence was below FL200, and 61 percent of all encounters were below 15,000. Take a look at an actual TAPS report from one of my flights at work. It’s included with this article and shows both the positive and negative “g” values that we encountered while flying through smallish, “popcorn,” or “cotton ball” cumulus clouds. A cumulonimbus monster would have been much worse.
Just the Facts, Ma’am
Thunderstorm hazards include ex- treme turbulence, hail causing severe structural damage, severe icing, torna- dos, lightning, microbursts, wind gusts over 50 knots, extreme rain, engine compressor stalls, flameouts, piston engine failures, loss of lift, zero visibil- ity and hydroplaning. Did you notice the occurrences of the words “severe” and “extreme?” If you fly through this crap, you’d better be wearing a diaper – you’re going to need one. Twin and turbine pilots operate in the same slice
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April 2019 / TWIN & TURBINE • 35