Plane & Pilot
Tuesday, March 11, 2014

The Season Of Turbulence

The summer heat is around the corner, and so is the cobblestone sky

Most pilots agree that summer is the favored season for flying. Aircraft engines may prefer winter with its cool, oxygen-rich air, but summer often brings less weather and fog, better visibility and generally more agreeable flying conditions.

That's not always the case, of course. In Alaska, we used to welcome the atmospherics of spring and fall, not quite so cold but still sweater weather, usually with patchy clouds and good visibility. There was just enough night chill to keep the bug population at bay during the day. Summers were our second choice for flying because the storms of winter were absent.

In the more southerly half of the U.S.—Texas, the Deep South and the Desert Southwest—summer brings better flying weather, but it also brings dismal heat. Airplanes don't perform as well in hot conditions, a function of higher density altitude that robs engines of power and wings of lift, and offers less stable air that makes airfoils less efficient.

One aspect of flying in warm weather that many pilots don't appreciate is turbulence. Non-pilots who fly the airlines sometimes remember nothing else about their flight other than how smooth it was—or wasn't. Passengers on commercial flights can become terrified that the airplane is about to disintegrate when a big Boeing or Airbus slams through turbulence and bounces mashed potatoes and peas on the roof in First Class.

Pilots generally know better. My first airplane was a Globe Swift, and flying around the California deserts back in the 1960s, I used to react to summer turbulence with the same apprehension. I thought every shock of rough air was at least 5 Gs, and I knew the little 20-year-old Swift wasn't nearly tough enough to take many of those jolts.

Only later, after I installed a G-meter in an empty instrument hole on the Swift's panel, did I discover that even some violent shocks would barely move the needle. It's a rare "air pocket" indeed that pushes the G-meter much past 2.0.

Turbulence can arise from a number of sources—mechanical, mountain wave, frontal activity—but in summer, the primary offender is convection. As the high sun heats the ground, convective turbulence chops up the sky, forming thermal activity near the ground and potentially violent cumulus clouds at higher levels.


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