AOPA Pilot Magazine - March 2012 - 95

but by midday winds sometimes reach a not-so-nice, gale level? (Definition: winds of 28 to 47 knots.) Then, as the sun sets, the winds magically die down. This behavior is a function of the mixing of air in the lowest levels of the atmosphere. At night, the winds aloft continue moving at their usual pace. But without any surface heating from the sun, surface winds drop off because there are no rising air parcels. But by late morning, the surface heats up a bit, which allows this warmer air to reach the 3,000- to 5,000-foot-agl level. This, plus the turbulence created at the boundary between the faster-moving winds aloft and the calmer surface winds, creates eddies that mix the winds aloft and send them downwards. The result? Winds pick up during the day. For a few days after a cold frontal passage, or on days when a large high pressure system prevails, you can generally rely on a rule of thumb to predict the peak strength of surface winds. It’s a simple rule, based on the air-mixing phenomenon. Just look at the winds aloft at 3,000 to 5,000 feet agl. By midmorning those winds will mix down to the surface. So if the winds aloft are 30 knots, by 11 a.m. they’ll be at ground level. At day’s end, those winds aloft will “decouple” from the quieter air nearer the surface and the pattern will become a tamer place. Hands and feet So much for theory. Remember the triedand-true piloting skills necessary for landing and taking off in nasty surface winds? Here’s a quick review of a few: • For a high-wind takeoff, it’s best to lift off firmly so that any downdrafts don’t let you settle back to the runway. For the same reason, leave the gear down in retractable-gear airplanes until you’re safely above the runway. • On final, use your normal approach speed, but add half the gust factor if winds are gusting. For example, if winds are 15 gusting to 25, then add half the difference (five knots) to your normal approach speed. • Don’t fly high-wind approaches with too much speed; it will take longer to bleed off lift and airspeed, you’ll be exposed to crosswinds for a longer period of time, and be subject to ballooning with the excess lift caused by any gusts. • Consider using partial flaps when the winds are high. In strong winds, full flaps make for more lift at slower airspeeds when in ground effect, something you
AOPA PILOT • 95 • MARCH 2012

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AOPA Pilot Magazine - March 2012

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