Big blows: flying safely in high wind conditions is a matter of adopting the proper technique for your aircraft's weight and configuration.
Call it what you will--Chinook, Santa Ana, Foehn or Borea--pilots who live in the lands of seasonal high winds know they must either learn to fly in them or sit grounded and watch the world blow by. What is their secret for flying safely in windy conditions?
Most pilots' strategy starts with reviewing the forecast. If you see "WND" tacked onto the outlook portion of an area forecast, you should know to expect more than 25 knots of breezy goodness the next day. Fast forward to the terminal aerodrome forecast (TAF) and look for PK WND in the remarks (RMK) section and you'll know gusts are expected to exceed 25 knots.
But how can you tell if the forecast is likely to come true? If you are the kind of person who swears by pictures (as I am), pull up the WIND/TEMP chart at ADDS, DUATS or other online weather resources. The color-coded patches and lines of isobars swirling around the high pressure and low pressure centers begin to give you a clue. Watch for tightly spaced isobars, as they have WND written all over them. Switch over to the prognostic charts and look at the actual placement of the high pressure and low pressure systems.
If you see them stacked one right above the other, or tightly clustered, imagine the counterclockwise motion of the low pressure grinding against the clockwise motion of the high pressure as two gears in a very large grandfather clock. See those isobars squeezed at the point of impact of those two systems? That's what just happened in southern California in early December, causing Santa Ana winds to slam a wide area with gusts above 100 mph.
Check the turbulence prediction charts that are a fairly new item in our weather repertoire, as high winds and rough rides often correlate. Pull up a satellite image and compare it to the prognostic charts to confirm what you've probably already figured out.
Want final vindication? Wake up the next day and check the pilot reports (Pireps) for the symbol WV and a series of numbers (example: 28060 for wind from 280 degrees, 60 knots). You'll know what the guys who got up early actually experienced. Yes, you can get all of this without ever looking outside at the trees and the windsock. See the sidebar on page 6 for some examples.
Getting all this information before we launch--or even roll out of bed--is a good thing, too, since ground interference means that what you see, wind-wise, out your window, may not be a good representation of what's actually blowing down (or swirling around) your local runway.
There are many causes for stiff winds, and if you live and fly in some of the more challenging terrain in the world, then you've probably learned from your first encounters there that flying light aircraft in high wind conditions is doable--if you know what you are doing.
Before we go much further in this discussion, let's clarify a few conditions. How much wind are we talking about here? Let's confine the discussion to what triggers a note on the forecasts: more than 25 knots, the stuff that makes even the largest windsock stand straight out and dance, kicks spray up off cresting waves, draws long streaks of foam on inland bodies of water and throws sand in your face--wicked stuff.
How light are the aircraft we are talking about? Well, I recently participated in sailplane operations in the Breede River Valley, near Cape Town, South Africa. The valley, rimmed by 4000-foot peaks on both sides, is known for steady howlers (when you see buildings chained to the ground and nothing tied down outside, that's always a good indicator of WND). However, it attracts proficient glider enthusiasts from all over the world with its combination of decent weather and consistent, powerful lift. When the wind howls, most of the lift is mountain wave, and the incredible rides it delivers is reserved for those who understand and can manage the kick-ass turbulence generated by the rotors and windshear beneath the wave.
Why do they do it? Because the sailplanes are stressed for the beating and because--above all that chaos, in the wave--flight conditions are often extremely smooth, with climb rates exceeding 1000 fpm. It is a heck of a free ride into the troposphere, and on a clear day provides the benefactor with weather balloon-like views of the Cape of Good Hope.
So, how do 300- to 1000-pound gliders operate safely in such wind? Well, to start with, they don't taxi out to the runway. Soaring is generally a team sport, and the Cape Glider Club supports its members. I saw no less than three souls handling each aircraft, one on each wing and one on the tail, as it was carefully maneuvered to the end of the soaring runway and set pointing into the wind with full spoilers deployed. There's a lesson in that for all of us. Statistics show that nearly 20 percent of taxi accidents in the NTSB database are caused by wind incidents, and of those, high-wing aircraft tend to succumb with the most frequency. It's not hard to understand why. Getting across the wind and running out of control authority (even with full, correct control inputs) will happen to lighter high-wing aircraft in high wind. If you can't get to the runway safely, do yourself a favor and don't start the engine.
The sailplane operator's strategy for a safe takeoff starts with an absolute in high wind--that is, absolutely no crosswind. Where the runway is wide, they'll accept a slight crosswind, but then negate it by setting up the takeoff diagonally on the runway, heading the glider straight at the prevailing wind. Next is an analysis of the gusts; too many and too much differential between the steady-state wind and the gusts is another no/go that cannot be fairly judged until you sit at the end of the runway prepped to go. Gusty conditions are indicative of windshear and rotors that might be generated by the steady-state winds hitting the obstructions near the runway (hills, trees and buildings) and churning. Imagine yourself in a washing machine, 'cause that's what it may feel like as your aircraft hits that fragile moment at [V.sub.R]. Not good for you or the machine.
If the wind field is clean and the windsock shows a steady-state condition, though, light aircraft manage safe takeoffs in conditions approaching 40 knots with some regularity. The key, however, is speed. With all that wind in your face the aircraft is going to want to fly. Keep it on the ground for an extra 10 knots or so, then expect a robust climb at your cruise-climb speed away from the danger zone close to the ground, where rotors and wind-shear are prevalent. The two-place training gliders operating on winch launches in the stiff winds went from 0 to 3000 feet of altitude in a minute flat before releasing from the cable into free flight.
Once aloft and approaching the mountain ridge (at a proper 45-degree angle, as any cautious pilot must do) you'd better tighten your seatbelt and hang on. The presence of ridge-line cap clouds, chewy-looking rotor clouds in the lee and your classic wave lenticulars means only one thing: turbulence ahead. Sailplanes are typically stressed for +10 g and -4 g; is your production airplane? If not, climb, and see if you can at least get above the rotor clouds before you approach the ridge. Many mountain-flying manuals suggest you put 2000 feet between you and the ridge for every 20 knots of wind-speed at altitude. Others recommend you simply avoid mountain-flying altogether once winds aloft exceed 20 knots, but if you are routinely flying in and out of valley airports you'll soon find that will ground you a lot.
Operating in the flatlands? Don't be surprised if you find smooth-air conditions above the friction zone (about 2000 agl). Try to plan trips for when that howler is a tailwind, though. This is particularly sage advice for pilots of slower aircraft, who might find their forward progress so impeded as to make any significant cross-country flight simply impractical (not to mention expensive).
More often than not, the real issue for pilots is that the winds have come up while they were flying, and now they've got to get down. (All the more reason to always check the forecasts!) If this happens to you and you aren't prepared to land in a heavy wind, consider diverting to an airport where the winds are lighter or at least more closely aligned with the landing runway. Not possible? Then remember the rules for taxiing and takeoffs in windy conditions, because they apply on landing, too.
Powerplane pilots should consider forgoing flaps completely in gusty conditions, and also consider reduced flaps in any high-wind landing. Keep your speed up by keeping the power spooled up and ready to respond to a gust or a lull, and fly the airplane all the way through the touchdown to the ramp. Remember: It is the crosswind that undoes even heavy aircraft--avoid it. Land on the diagonal or land on a crossing taxiway if you must to eliminate it.
Very light aircraft pilots should take a lesson from glider pilots and keep the downwind short and the baseleg tight, as a heavy wind will push you quickly out of the pattern area, and leave you with a long and possibly punishing final approach (flying a Cessna 182, we were once vectored to a 10 nm final ILS into a 40-knot breeze in St. John, Newfoundland--and the ensuing approach through a solid overcast took 10 minutes to complete!). Just do the math. If your typical final approach speed is 75 knots and you are flying into a 40-knot wind ... yeah, now you get it. Of course, there's no need to slam on the brakes at touchdown; in fact, lighter aircraft might have to add power to keep rolling to the turn off!
Speaking 01 which, once you touchdown, don't relax. If you are in a high-wing bird, seriously consider rolling right to the end and stopping, then acquire wing-walkers to hold your wingtips and usher you across the wind and into the tiedown area. Religiously use your ailerons and elevators to correct for wind, and minimize the time you spend exposed to cross-winds, even if it means taking a longer route to the ramp or tying down the aircraft in a different spot than usual. Look for a path to the ramp that utilizes foliage or buildings to limit your exposure to the wind. Watch the doors as you open them, as the wind has been known to grab big ones and yank them right off their hinges, sending them careening like tumbleweeds across the tarmac. If you must tie down on a windy ramp, orient your aircraft directly up or downwind and get your internal and external control locks in quick. Then tie down tight and double-or triple-chock the wheels, just for good measure.
HOW MUCH IS TOO MUCH?
So, how much wind can you fly in? Well, keep this in mind: airliners typically suspend operations when winds roar above 50 knots (or at lower wind speeds if crosswinds or gust are prevalent). Those aircraft weigh up to one million pounds loaded, so don't think you can do better in your 4000-pound bird. Follow their lead and cancel your takeoff.
Operating in high wind conditions with a light aircraft is not for sissies, but skilled pilots who live and fly in areas where 25-knot winds are a regular phenomenon manage safe flights all the time, and you can, too, once you understand the "gotchas" and how to avoid them.
Regardless of whether you're planning a local hop or a continent-spanning flight, one great tool is the winds aloft chart, an example of which is reproduced above.
When considering this chart, the color-coding is as important as the isobar (the black lines) spacing. When grouped tightly together--like over western Canada, the U.S./Mexico border and New England, for example--you can count on stiffer winds and possible turbulence.
Use this chart for various purposes, including picking an altitude: This is the 500mb winds aloft chart, corresponding to FL180. Other charts depict forecast winds at different levels. Pick the one that's best for you and go fly.
RELATED ARTICLE: TAILDRAGGER AND FREE-CATERING NOSEWHEEL PILOTS TAKE NOTE
You know what happens when wind blows on your aircraft from the side during takeoff or landing. Things get interesting, don't they? For you who fly taildraggers or airplanes with free-castering nosewheels, you should understand your crosswind limitation is key to safe taxiing, takeoffs and landings.
These aircraft want to weathervane into the wind at every turn, and must be steered using differential braking against the crosswinds. Cirrus SR20 and SR22s, with their tightly cowled mains, have been plagued by wheel-pant fires started by overheated brakes, and taildraggers in general have an abysmal accident record that cannot be blamed on the aircraft (if the pilot hadn't put the aircraft into those conditions there would have never been an accident, I maintain).
If you must operate in high winds, heed the rule: no significant crosswind component for you. Your airplane and your insurance company will thank you.
Amy Laboda is a freelance writer, CFII-MEI and a National Lead FAAst Team representative. She holds on ATP and flies two experimental aircraft: one that's sweet and slow and one that's pretty and fast.
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|Title Annotation:||STICK AND RUDDER|
|Date:||Jan 1, 2012|
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