You studied the terminal forecast, listened to the automated weather observation, and determined which runway local traffic is using. Now a confirming glance at the windsock will give you your best sense of the wind before takeoff.
Returning to the airport, it’s the same idea; if the AWOS broadcast says one thing and the windsock says something else, well, seeing is believing.
Obviously a limp windsock indicates calm air, and a windsock that’s fully extended alerts you to significantly windy conditions. (A straight-out windsock snapping in a firm breeze is the opening image of many “hangar stories” about flying, or not flying, on a windy day.)
But don’t rely on fearless-flier tales to interpret wind values implied by a straight-out sock. The FAA offers this advisory circular with general guidelines for the size, installation, and material strength of most windsocks, and how they should perform under various wind conditions.
To a pilot operating an aircraft, the most important of those guidelines are those that call for a windsock to move freely about its vertical shaft, and indicate the true wind direction within five degrees (plus or minus) when subjected to wind of three knots or more. A fully extended windsock that meets the guidelines indicates surface wind of at least 15 knots. It is therefore logical to conclude that a windsock alternately partially extended and fully extended is indicating gusting conditions with gusts up to or exceeding 15 knots.
Be sure to note the direction, or directions, in which the windsock is pointing, both to get some idea of the crosswind factor and to observe the rate and extent of wind direction changes.
As noted, windsocks may provide indications that conflict with officially reported winds. But what should you do if the windsocks at a multiple-windsock airport contradict each other?
“There are many airports where swirling winds can result in unusual conditions, such as two windsocks at opposite ends of the runway pointing at one another,” noted this April 2015 article in Flight Training magazine’s “How it works” series. “What matters to you is the windsock nearest your point of liftoff or landing. Windsocks are critical during taxi as well, to limit the effect of the wind through proper positioning of the aileron and elevator controls.”