Airspeed & Turbulence: Easy Adjustments

The airspeed indicator always has been one of a pilots most useful tools for measuring aircraft performance. Its colorful, with white and green, maybe a pair of red lines and a blue one, and maybe some yellow. And theres that big white needle we use for bragging rights. Early on, we were taught some of the most important speeds we need to know and use arent marked on it. One of them is the airplanes design maneuvering speed (VA), sometimes confused with the turbulent air penetration speed, which perhaps is better known as design speed for maximum gust intensity (VB).But is there a difference between VA and VB? What is it, and when do you use them? Why? Which should we be concerned more with as a pilot, and when? And airplanes are stressed to lower negative-G limits than their positive G-load limit-what about negative-G encounters in turbulence? Lets look at the operational reality of airspeed and G-load control in turbulent air.

Tom Turner

Friday, December 11, 2015 at 12:00 AM ET

Verified

Key Takeaways:

Design maneuvering speed (VA) is the maximum speed for applying abrupt control inputs without exceeding the aircraft's positive G-load limit (the aircraft will stall first); its effective speed decreases with lighter aircraft weight.
Maximum gust speed (VB), or a weight-adjusted VA when VB is not specified by the manufacturer, is the recommended turbulence penetration speed, allowing the wing to stall and shed G-loading before structural damage from severe gusts.
Pilots must account for significantly lower negative G-load limits in turbulence and should slow down well below the weight-adjusted VA/VB (e.g., 20-25 knots below) *before* entering suspected turbulent air to provide a safety margin against both positive and negative G-forces and accelerated stalls.

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The airspeed indicator always has been one of a pilot’s most useful tools for measuring aircraft performance. It’s colorful, with white and green, maybe a pair of red lines and a blue one, and maybe some yellow. And there’s that big white needle we use for bragging rights. Early on, we were taught some of the most important speeds we need to know and use aren’t marked on it. One of them is the airplane’s design maneuvering speed (VA), sometimes confused with the turbulent air penetration speed, which perhaps is better known as design speed for maximum gust intensity (VB).

But is there a difference between VA and VB? What is it, and when do you use them? Why? Which should we be concerned more with as a pilot, and when? And airplanes are stressed to lower negative-G limits than their positive G-load limit—what about negative-G encounters in turbulence? Let’s look at the operational reality of airspeed and G-load control in turbulent air.