October 2004Features

Wing low, opposite rudder

Or crab and kick -- but crosswinds demand respect


Tackling a tough crosswind landing can be one of the more psychologically challenging tasks facing the student pilot. It has all of the stresses of a normal landing, plus the added pressure of placing the aircraft in an unfamiliar and initially uncomfortable position for touchdown. Touching down on the upwind main wheel, then the downwind main, and finally the nosewheel may sound logical, but it takes a lot of patience, practice, and confidence. Overcoming the apprehension that naturally occurs close to the ground is the first step toward gaining the confidence to start experimenting with the control inputs needed to arrest the drift associated with a crosswind landing. Learning crosswind landings is like learning a dance, step by step. With practice, it should eventually become smooth as silk.

A stable approach

Crosswind
Control inputs for a crosswind can briefly vary -- sometimes dramatically -- if the wind is gusty or its direction variable.
Crosswind
Touch down first on the upwind main wheel, then downwind main, and nosewheel last

A successful crosswind landing -- or any landing, for that matter -- begins with a stabilized approach. A stabilized approach means that the airplane is maintaining target airspeed and descent rate, is on glide path, and is properly configured for the landing. Flying a stabilized approach simplifies the pilot's task of mentally projecting the aircraft's three-dimensional flight path and applying control inputs to maintain the approach path. Significant speed and configuration changes during an approach can complicate controlling the aircraft, especially in gusty or turbulent conditions that can be associated with crosswinds.

In general, two types of approaches are used in crosswind conditions. The crab method is simply turning the airplane's nose into the wind to compensate for drift. In this way, even though the airplane's nose is not pointed at the runway, the airplane's ground track is along the extended centerline of the runway. Just before touchdown the crab is removed or "kicked out," and the upwind wing is lowered into a slip (don't forget to add opposite rudder, too). During the approach, this method is arguably more comfortable for the passengers.

When using the wing-low or sideslip method, the upwind wing is dipped or rolled into a very slight bank toward the wind. This small bank angle compensates for sideward drift. Because the airplane wants to turn into the wind, opposite rudder is used to align the longitudinal axis of the airplane with the extended centerline of the runway. Thus, bank angle is used to control lateral (side-to-side) drift, and rudder is used to align the fuselage.

Many pilots use a combination of these two methods. They will use the crab method until reaching some predetermined height above the surface, for example 1,000 feet above ground level. Then they will transition to the wing-low method until touchdown. This combination method works well because eventually you will have to place the airplane in a wing-low attitude for landing to minimize side loads on the landing gear. And it is easier to transition at a higher altitude than it is to transition close to the ground. If the crab method of drift correction is used throughout the final approach and roundout, the crab must be removed before touchdown by applying rudder to align the airplane's longitudinal axis with its direction of movement. Concurrently, the upwind wing must be banked to compensate for lateral drift. This is generally more challenging and requires timely and precise rudder and aileron action. Moreover, failure to accomplish this alignment results in severe side loads being imposed on the landing gear and imparts ground-looping tendencies.

Finally, two other factors must be considered on approach. The first is final flap setting. Fully extended flaps (think barn doors) create a large surface for the wind to work on, and in gusty conditions, this can make the airplane more difficult to control. If your pilot's operating handbook (POH) allows it, and runway length is not an issue, consider using a partial flap setting instead of full flaps. But remember to increase your target approach airspeed based on the flap setting that you select. You will find recommended airspeeds for various flap settings in your POH. A partial flap setting will improve airplane controllability in two ways. First, because you've reduced the flap surface area for the gusty winds to work on, the airplane won't get buffeted as much as with full flaps. Second, the higher approach airspeed will increase lateral control of the airplane because the faster airflow over the ailerons results in improved aileron effectiveness.

The second factor is adjusting your approach airspeed for wind gusts. Conventional wisdom is to add one-half of the gust amount. For example, in the first case, if the wind is 160 degrees at 14 gusting to 24, that is a 10-kt gust. If your approach airspeed is normally 60 kt, you would fly your approach at 65 kt (60 plus 5).

The added airspeed is extra insurance for a sudden loss of airspeed close to the ground. Keep in mind, however, that any increase in approach airspeed will result in a longer landing distance. You also may find yourself fighting the crosswind close to the ground, where ground effect can make it more difficult to slow down. You should consult your flight instructor and your aircraft's POH for further guidance on this issue.

The roundout and flare

If the wing-low approach is used, the crosswind correction (aileron into the wind and opposite rudder) should be maintained throughout the roundout and flare, with the touchdown made on the upwind main wheel. As the airplane slows, the weight of the airplane will cause the downwind main wheel to gradually settle onto the runway. The nosewheel should be gently lowered to the surface last. If the crab approach is used, the crab must be "kicked out" just before touchdown to align the airplane with the runway centerline. This requires good stick and rudder skills and superb timing. The airplane should not be allowed to touch down with any appreciable lateral drift, because this creates side loads that could damage the landing gear and can cause directional control problems.

Quality time

Learning these crosswind techniques and the effects of the controls takes time, but unfortunately, students don't get much time to study. By and large, the roundout to flare and landing takes only 10 to 15 seconds. In a typical hour of pattern work, this equates to roughly three minutes of practicing these critical skills. However, instructors can give students more time "in the zone" (the last few feet until touchdown) by making a series of low passes over the runway in the landing configuration and airspeed. This will allow students more time to develop a feel for the effects of the controls.

First, you'll need to find a suitable runway for this roundout practice. For an average trainer, it should be at least 5,000 feet long and the wider the better. Make sure there are no obstacles in your takeoff path because you may be at a lower altitude than usual during climbout. A crosswind would be nice but is not required. After the instructor establishes the aircraft in slow flight just a few feet above the runway, the student takes control of the airplane. The instructor maintains control of the throttle and adjusts it to keep the wheels a couple of feet above the pavement. It's OK if the wheels inadvertently touch down during the exercise.

As the student motors down the runway, he'll be able to see how pitch inputs affect the airplane's height above the runway, and how very small amounts of bank affect the airplane's lateral movement. He'll discover how very small rudder pressures swing the airplane's nose around. Finally, with a safe amount of runway remaining, the CFI applies full power and the student begins a go-around. Give throttle control back to the student at a safe altitude.

Another valuable teaching technique is for the instructor to handle three controls at once to allow the student to master just one control at a time. For example, the instructor can control throttle, pitch, and bank while the student uses rudder to keep the longitudinal axis of the airplane parallel to the runway. To help the student "see" the aircraft's longitudinal axis, put a strip of masking tape on top of the cowling. It should stretch from the front of the cowling to the base of the windscreen in front of the student-and, of course, be aligned with the aircraft's longitudinal axis. The instructor can estimate for the student the airplane's height above the runway, whether there is any lateral drift, and whether the longitudinal axis is aligned. This will help the student learn to estimate these variables by himself.

On another pass, the instructor might control the throttle and the rudder while the student wrestles with pitch and bank inputs. It may take a number of these low passes for a student to get the picture. As his skill increases, give him full control of the approach and low pass and challenge him to fly with the wheels a specified height above the runway. Slowly reduce the target height, and soon the student will start greasing it on because he is trying to keep the wheels 6 inches off the runway instead of landing. These low passes are a great way to develop a sense of control inputs and the airplane's reaction (see "CFI to CFI: Show and Tell," April 2004 AOPA Flight Training).

The rollout

After the wheels start rolling on the pavement, don't get distracted by extraneous tasks such as raising the flaps, tuning the radio, or opening a window. Especially with crosswinds, it is crucial that the airplane be controlled with the flight controls until it is stopped. As the airspeed decreases, the airflow over the flight controls is reduced, and the controls become less effective. Full deflection of the ailerons may be prudent to keep a wing from lifting or the airplane from being pushed off the side of the runway.

Many aircraft incidents occur during this phase of landing. It happens this way: After a brutal approach, a pilot makes an amazing crosswind landing. Relieved to be on the ground, he lets down his guard and forgets that he still needs to fly the aircraft until it is completely stopped. A small gust of wind catches the tail, and the airplane begins to swerve. Surprised, the pilot kicks hard rudder, but the input is late. A dash of overcontrolling combined with some pilot-induced oscillations causes the airplane to depart the runway surface and come to an ignoble rest.

You should find a maximum demonstrated crosswind velocity published for your airplane in the POH. This figure, although not a legal limitation, is provided for informational purposes only but is a good number to memorize and comply with. This is the maximum (90-degree) crosswind component in which a factory test pilot demonstrated a safe landing during certification. To pass certification, the airplane must have been shown to exhibit satisfactory controllability and handling characteristics during landing on a dry runway with this amount of crosswind. Most POHs also include a crosswind component chart that can be used to determine the headwind (or tailwind) and crosswind components given the runway heading and wind direction and speed.

The problem is that these charts never seem to be handy when you need them the most. That's where a simple gouge -- or rule of thumb -- called the "five dollar and 79 cents rule" ($5.79) comes in handy. This allows you to quickly estimate the crosswind component without consulting a crosswind component chart. The numbers five, seven, and nine mean that for a 30-degree crosswind, the crosswind component is 50 percent of the reported steady state wind. For a 45-degree crosswind, the component is 70 percent of the reported steady state wind. For a 60-degree crosswind, the component is 90 percent of the reported steady state, or for all intents and purposes, the full amount. For example, if the difference between the runway and the wind direction is 45 degrees, and the reported wind is 20 kt, the approximate crosswind component is 70 percent of 20, or 14 kt.

As long as you're not pushing the envelope, this rule of thumb works quite well. If you ever run out of control travel and can't arrest the aircraft's drift, go around.

Personal limits and currency

If you are pushing the envelope, by all means use the chart, and figure the crosswind exactly. (Unless the wind is really steady, it won't be exact anyway.) It's also a good idea to have a predetermined personal limit for dealing with crosswinds. If you're a student, it's your instructor's responsibility to set the limit on how much crosswind you can fly solo in. (See "Student Supervision," p. 73.) But a private pilot has no such limit.

In this case, a preset limit will keep you out of trouble because the decision of continuing the approach or finding a different runway more favorably aligned into the wind is already made. If a different runway with less crosswind is not available, then the prudent action is to proceed to an alternate airport with a more favorable runway alignment. Usually, if there is no preset limit, the limits for what crosswind you're willing to take are directly proportional to how much vested interest you have in landing at that particular airport. That's a risky proposition.

The crosswind landing is a little more challenging than a normal landing and requires a little bit more skill and finesse. You must simultaneously arrest the airplane's lateral drift with the ailerons and align its longitudinal axis with the runway centerline using the rudder. However, once you get used to them, they are really no more difficult than a normal landing.

Keeping current on crosswind landings is another matter. Practice them whenever you can -- as a minimum, make at least three crosswind landings every 90 days. If you are uncomfortable or apprehensive about practicing them, take your flight instructor along for recurrent training.

Having a predetermined personal limit will help to keep you safe. If you ever find yourself thinking, This crosswind isn't so tough, remember that experienced pilots have gone from hero to zero while thinking the exact same thing. Fly safe.

Christopher L. Parker is a CFI and an aviation author, speaker, and FAA remedial training specialist. He is captain of a Canadair Challenger business jet based in Van Nuys, California.

Want to know more?

What would happen if you had to divert on a cross-country and the crosswind at the new destination was a monster? The AOPA Air Safety Foundation's DVD, Lost and Crossed, provides helpful advice on crosswind landings and gusty wind conditions. Go to AOPA Online to find links to ASF resources and additional information about topics discussed in this article.


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