March 1, 2001
Pilots can view strong winds as either a curse or a blessing. Fifty-knot tailwinds aloft for that long cross-country flight? Great! Twenty gusting to 30 knots, blowing at 90 degrees to your destination's 2,000-foot-long, 50-foot-wide active runway? Bad, bad news. For these and so many other reasons, pilots cultivate a strong interest in any weather report or forecast involving the wind's behavior. That's because, in the final analysis, adverse winds can represent a lot more than a rough ride and unscheduled fuel stops. According to an AOPA Air Safety Foundation Safety Review, General Aviation Weather Accidents: An Analysis and Preventive Strategies, loss of control while landing or taking off in crosswinds caused 987 accidents between 1982 and 1993, making botched crosswind landings one of the biggest categories of general aviation accidents. Most of those accidents didn't involve fatal injuries, but there were plenty of minor and serious injuries, and the insurance claims must have added up to a pretty penny indeed.
To be brutally simple, wind is caused by differences in atmospheric pressure. Let a low-pressure system move up against a high-pressure system, and the compression of air between them can set up a steep pressure gradient. This compression shows up on surface analysis and winds aloft charts as closely spaced isobars (surface charts) (winds aloft charts). Either way, the result is the same. The more closely packed the isobars or height contours, the greater the pressure differential and the stronger the wind.
Temperature contrasts between two differing air masses can also play a big part in creating wind. Warm air is lighter and rises, while cold air is denser and sinks. Nature abhors a vacuum, so when one parcel of air rises, the air around it rushes in to take its place. It's this simple dynamic that causes land and sea breezes along shorelines, valley winds, and surface winds where convection is present.
Think about that temperature-wind relationship the next time you fly. Ever wonder why surface winds so often begin to pick up in midmorning, reach their peak at the warmest time of day, and then die down by late afternoon or early evening? Absent any frontal passages or storm systems, it's because solar energy heats up the surface, which in turn heats up the air above it, which in turn causes thermals, which in turn cause the air nearby to rush in to fill the "vacuum" left by the rising air. This diurnal (daily) process also plays a huge role in the shoreline breezes just mentioned.
Pilots should know when to anticipate strong winds — especially strong surface winds. Sure, a good weather briefing ought to mention adverse surface winds via an Airmet Tango. This type of airmet, like all the rest, shows up at the beginning of an area forecast, right after the synoptic summary, and is certain to be given top billing by a flight service weather briefer. Airmets Tango warn of nonconvective turbulence, low-level wind shear, and strong (sustained winds of 30 knots or greater) surface winds. In addition, the outlook portions of a terminal aerodrome forecast (TAF) should forecast any sustained surface winds greater than 15 knots, gust value changes of 10 knots or more, and wind direction changes of 30 or more degrees.
But a well-educated pilot should be able to look at a few charts and decide for him- or herself if there's a setup for adverse wind. Here's what to look for:
This is really a subject for another article — nay, a book! — but it's certainly appropriate to review the basic techniques for landing in crosswinds. Most instructors seem to favor the crab-and-slip method.
But first things first. Well before you enter an airport's traffic pattern, you should learn about the surface wind conditions from flight watch (on 122.0 MHz), approach control, AWOS, ASOS, ATIS, or unicom. This gives you a good idea of the strength of the crosswind component affecting the airport's runway(s), and allows you to recollect your airplane's maximum demonstrated crosswind component. This figure, published in the Normal Procedures section of late-model pilot operating handbooks (POHs), is frequently listed at the head of the chapter, among the "airspeeds for safe operation." This figure — let's say, 17 knots — is not a limitation. Your skill level may be such that you could safely land in a 25-knot direct crosswind. It's just that on the day the manufacturer scheduled the crosswind tests, the winds happened to have the posted crosswind component. Even so, the maximum demonstrated crosswind component is a good warning sign. That sign says, "Go ahead and try this at home, but our test pilots may not have landed in conditions any stronger than this." So if you're looking at landing in a 25-knot crosswind, it's time to ask yourself, first, "Have I landed in these conditions before, in this airplane, and am I skilled, practiced, and confident enough to handle them?"
If the answer is "yes" then give it a try, but be ready for a go-around. If it's no, then it's time for that second question: "Do ya feel lucky?"
Anyway, after knowing the surface wind, confirming it by observing the windsock, and — if you're landing at an airport so equipped — hearing from the tower of any low-level wind shear alerts, you're ready for the approach. In the crab-and-slip method, the steps are as follows:
Maintaining directional control of tailwheel airplanes is much more difficult than steering those with nosewheels. This is because a tailwheel airplane's center of gravity is behind the main gear, rendering it much, much more susceptible to weathervaning into the wind. Apart from this consideration, tailwheel airplane landings in strong or gusty winds can be conducted the same as those of a nosewheel-equipped airplane. Some may prefer wheel landings (touching down with the main gear first, then allowing the tail to drop as the airplane slows), but this technique is only for the skilled. You'll be doing a foot-blurring tap dance on the rudder pedals in a crosswind, and the penalty for getting out of step is usually a mean ground loop. It's better to touch down in a three-point attitude with the tailwheel on terra firma, where it can better help the rudder and ailerons in slowing and steering.
Landing in strong, gusty crosswinds is never much fun, but you can become good at it. As with every other challenging maneuver, the best way to earn and keep proficiency is to tackle hairy crosswinds with an adept instructor, maintain your proficiency by taking on crosswinds on your own, and seek out recurrent instruction. No doubt about it — high winds mean hard work!
Links to additional information on flying with the wind may be found on AOPA Online ( www.aopa.org/pilot/links/2001/links0103.shtml). E-mail the author at firstname.lastname@example.org.
Safety and Education,
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