Windsock Value in an Era of GPS? Very, Sort of, Sometimes.

Our windsock in front of cabin and plane

A contemporary pilot, outfitted with GPS and other equipment, might understandably wonder why a simple, old fashioned airport windsock is still useful.  Who cares?   Bush pilots, among others. 

For one thing, even GPS systems rarely show ground speed at destination.  For another, ours conks out below about +10 degrees on winter flights in our cold Piper PA-20.

The first time this happened, my husband stuffed the tablet between his body and his quilted Carharrts to warm up, but it still did not turn on for 20 minutes, which happened to be the duration of the flight from the nearest airport to our home.  Fortunately, this was a familiar route.  But the mountainous terrain, rivers, glaciers, woods, and bogs result in very different wind, ice, snow, and temperature over very few miles, here.  It is not safe to presume a condition at another location.  The bright orange windsock next to a runway is, therefore, a welcome source of at least one piece of critical information.

  At federally funded airports, windsocks must comply with FAA mandates for size, length, fabric and inlet and exit diameters.  All these factors ensure uniform interpretations of wind direction and strength as ascertained by the angle at which the sock hangs.  Ninety degrees (horizontal) indicates a wind at or above 15 knots.  Striped windsocks are particularly easy to read for lower speeds, as the droop of each successive stripe is supposed to reflect increments of 3 knots. But that is hard to see from the air.  Perhaps this is yet another reason to give binoculars to a passenger.  However, some aviation writers dispute the accuracy of the number of knots per stripe.

It is important for pilots flying to and from other locations, such as rural airports, lodges and personal airstrips to realize that non-FAA windsocks LACK this uniformity.  They vary in size, fabric, age, and aperture dimensions, so their wind speed indicators are calibrated differently by each manufacturer.  For example, in the chart by one vendor, below, a fully extended 3.6 meter windsock indicates a wind speed 2.3 times faster than an erect 1 meter sock.

Old, faded weather-beaten socks have surely lost their water protection and may be degrading with thousands of pin prick holes in fraying fabric, leaching air like water through a sieve.  They can still rotate to point out wind direction, but will convey inaccurate wind speeds.

At our home, we first relied on two inexpensive anemometers hoisted above the tree line on our solar/wind tower.  Both broke.  At least the wind turbine provides some information at about 200 feet above the lake where we land.  This year, we went “low tech” and bought a 54” windsock (from Northern Lights Avionics at Merrill Field in Anchorage).  We installed it near the middle of our landing strip on the frozen lake, far from the heavily treed shoreline and in line with the prevailing north winds that blow across a large, flat bog.  We hope that by using it only in winter (we rely on water movement to land on floats in summer), the fabric may last twice as long as expected.

We also bought a handheld anemometer ($40) to learn to read the windsock with more accuracy.

From our cabin, we hear the wind gusts in the surrounding trees and detect it from snow blown about the lake in swirls, eddies, and dunes, but had not measured it well before.  Now, when my husband is ready to fly home, I can report speed, direction, and variability data viewed from my kitchen window or outside so he can anticipate his landing strategy.

Every winter bush pilot knows the value of low tech indicators- like reading wind by tree bends and snow blow patterns.  An orange windsock in a black and white world is an easy-to-see asset.  Just don’t presume, from the air, that the length and age convey the same speed and direction information as those you have relied on at other locations.