Too many airlines think we can’t handle the truth, and so the flight crew refers to “bumps” rather than turbulence. You’ll even hear media types occasionally mention “air pockets,” a long outdated terminology. For light GA, turbulence is often uncomfortable and occasionally dangerous.
The Air Safety Institute, working with the FAA and the NTSB, is highlighting turbulence this month as part of our 2014 weather education campaign. Turbulence comes in a variety of forms and can be merely aggravating or really bad news.
Convective turbulence from thunderstorms is probably the worst and disassembles aircraft about six times a year. It often takes the form of the pilot first losing control, and then the hardware starts to come apart after all speed limits are exceeded.
But sometimes the bounces are in the form of waves and rotors. If you’ve done much flying in any sort of mountainous or hilly terrain you’ve likely experienced the wave—sometimes visible with lenticular clouds but not always, especially when the air is dry.
My first exposures to the wave were perplexing at best. In cruise flight with the autopilot in “altitude hold,” the airspeed was going up and the A/P was trimming nose down. Pretty cool—free lunch? You know the deal on lunches, because a few miles down the road just the opposite happened as the nose went up and the airspeed just went to pot. Thinking a navigational error had placed me into the Bermuda Triangle I called ATC to ask for a block altitude. It was, of course, the smooth part of the down wave.
However, altitudes below the smoothness can be a dentist’s delight—rough enough to jar loose fillings. Airspeed control is the key, and on descent in those types of conditions one should be well acquainted with VA—maneuvering speed. VA is one of those counter-intuitive concepts. As the gross weight declines, the slower the maneuvering speed. The published number in the handbook or on the placard is appropriate at max gross. If you’re lighter than that—slow down.
Airspeed bumps around a good bit in turbulence, and if everything is stable “right at” VA, a gust can increase the speed by 10 knots in the blink of an eye. When flying an older aircraft there is no comfort knowing that if the bozo that flew it before you exceeded VA, and got into heavy turbulence, some of the margins built into the structure when new have been used up. How much? Good question. Slow down.
Pay attention to pireps and Center Weather Advisories—the loss of a modified Cessna P210 is instructional. Even moderate winds over big mountains deserve to be treated with great respect. Maybe there’s something to this air pocket thing after all.