Aero-Tips!

A good pilot is always learning -- how many times have you heard this old standard throughout your flying career? There is no truer statement in all of flying (well, with the possible exception of "there are no old, bold pilots.") It's part of what makes aviation so exciting for all of us... just when you think you've seen it all, along comes a scenario you've never imagined.

Aero-News has called upon the expertise of Thomas P. Turner, master CFI and all-around-good-guy, to bring our readers -- and us -- daily tips to improve our skills as aviators, and as representatives of the flying community. Some of them, you may have heard before... but for each of us, there will also be something we might never have considered before, or something that didn't "stick" the way it should have the first time we memorized it for the practical test.

It is our unabashed goal that "Aero-Tips" will help our readers become better, safer pilots -- as well as introducing our ground-bound readers to the concepts and principles that keep those strange aluminum-and-composite contraptions in the air... and allow them to soar magnificently through it.

Look for our daily Aero-Tips segments, coming each day to you through the Aero-News Network. Suggestions for future Aero-Tips are always welcome, as are additions or discussion of each day's tips. Remember... when it comes to being better pilots, we're all in this together.

Aero-Tips 05.18.06

Microbursts are small scale, intense downdrafts that, on reaching the surface, spread outward in all directions from the downdraft center. Imagine turning a garden hose on high and then pointing the spray directly down at a sidewalk—what happens to the water is sort of like what happens with descending air in a microburst. Microbursts cause extremely hazardous vertical and horizontal wind shears at low altitudes as high-speed air exists close to calmer skies.

(Above graphic from the Aeronautical Information Manual)

Microbursts are not easily detectable by conventional weather radar or wind shear alert systems, because they are small, of short duration at any point on the ground, and they can occur over areas without surface precipitation—remember that radar sees rain or snow, not wind patterns.

Low- to mid-altitude cumulus clouds produce microbursts. Microbursts commonly occur in the heavy rain portion of thunderstorms, once strong downdrafts have developed. But they can also descend from much weaker, benign-looking convective cells that have little or no precipitation reaching the ground.

Microburst characteristics

• A microburst downdraft is typically less than a mile across as it descends from the cloud base to about 1,000-3,000 feet above the ground. Below that height, the downdraft changes to a horizontal outflow that can extend to approximately 2 1/2 miles in diameter.
• The downdrafts can be as strong as 6,000 feet per minute. Horizontal winds near the surface can be as strong as 45 knots resulting in a 90 knot change in wind speed across the microburst. These strong horizontal winds occur within a few hundred feet of the ground—where you'd have little room to recover from a windshear event.
• Microbursts can be found almost anywhere that there is convective activity. They may be embedded in heavy rain associated with a thunderstorm or in light rain in benign appearing virga (precipitation that evaporates before hitting the ground). When there is little or no precipitation at the surface accompanying the microburst, a ring of blowing dust may be the only visual clue of its existence.
• An individual microburst will seldom last longer than 15 minutes from the time it strikes the ground. The horizontal winds increase during the first five minutes, with the maximum intensity winds lasting approximately 2-4 minutes. Sometimes microbursts concentrate in a line and area activity may continue for as long as an hour. Once microburst activity starts, multiple microbursts in the same general area are not uncommon.

Aero-tip of the day: Visualize where microbursts may appear beneath and downwind of large cumulus clouds—and stay well clear of microbrusts.

FMI: Aero-Tips