Avoiding loss of aircraft control

Flying in the Central Valley usually does not give us much practice in handling cross-winds. In actuality, most Central Valley pilots enjoy perhaps the best weather flying conditions in the entire United States. That is, whenever it’s VFR, it’s pretty good VFR with excellent visibility and calm or moderate winds on the surface. Still, what happens when we desire to "fly-out" to Harris Ranch airstrip for some excellent dinning only to find the wind is 230° at 25 gusting to 30 mph.? Well, we could go back home to FCH (home base) or attempt the landing in the gusty winds. So, you ask yourself, I’m OK, I can handle the cross-wind, but let me quickly review in my mind what is the best course of action.

Source: AC 61-21A Flight Training Handbook.

Crosswind Approach and Landing

Crosswind landings are a little more difficult to perform than are crosswind takeoffs, mainly due to different problems involved in maintaining accurate control of the airplane while its speed is decreasing rather than increasing as on takeoff. There are two usual methods of accomplishing a crosswind approach and landing. They are the crab method, and the wing-low method. Although the crab method may be easier for the pilot to maintain during final approach, it requires a high degree of judgment and timing in removing the crab immediately prior to touchdown. The wing-low method is recommended in most cases, although a combination of both methods may be used.

Crosswind Final Approach

The crab method is executed by establishing a leading (crab) toward the wind with the wings level so that the airplane’s ground track remains aligned with the centerline of the runway. This crab angle is maintained until just prior to touchdown, when the longitudinal axis of the airplane must be quickly aligned with the runway to avoid sideward contact of the wheels with the runway. If a long final approach is being flown, the pilot may use the crab method until just before the roundout is started and then smoothly changing to the wing-low method for the remainder of the landing.

The wing-low method will compensate for a crosswind from any angle, but more important, it enables the pilot to simultaneously keep the airplane’s ground track and the longitudinal axis aligned with the runway centerline throughout the final approach, roundout, touchdown, and after-landing roll. This prevents the airplane from touching down in a sideward motion and imposing damaging side loads on the landing gear.

To use the wing-low method, the pilot aligns the airplane’s heading with the centerline of the runway, notes the rate and direction of drift, then promptly applies drift correction by lowering the upwind wing. The amount the wing must be lowered depends on the rate of drift. When the wing is lowered, the airplane will tend to turn in that direction. It is necessary, then, to simultaneously apply sufficient opposite rudder pressure to prevent the turn and keep the airplane’s longitudinal axis aligned with the runway. In other words, the drift is controlled with aileron, and the heading with rudder.

The airplane will now be side-slipping into the wind just enough that both the resultant flightpath and the ground track are aligned with the runway. If the crosswind diminishes, this crosswind correction must be reduced accordingly or the airplane will begin slipping away from the desired path. To correct for very strong crosswind, the slip into the wind must be increased by lowering the upwind wing a considerable amount. As a consequence, this would result in a greater tendency of the airplane to turn. Since turning is not desired, considerable opposite rudder must be applied to keep the airplane's longitudinal axis aligned with the runway.

In some airplanes, there may not be sufficient rudder travel available to compensate for the strong turning tendency caused by the steep bank. If the required bank is so steep that full opposite rudder will not prevent a turn, the wind is too strong to safely land the airplane on that particular runway with those wind conditions. Since the airplane's capability would be exceeded, it is imperative that the landing be made on a more favorable runway either at that airport or at an alternate airport.

Flaps can and should be used during most approaches since they tend to have a stabilizing effect on the airplane. However, the degree to which flaps should be extended will vary with the airplane’s handling characteristics, as well as the wind velocity. Full flaps may be used so long as the crosswind component is not in excess of the airplane’s capability or unless the manufacturer recommends otherwise.

Crosswind Roundout (Flare)

Generally, the roundout can be made as in a normal landing approach but the application of a crosswind correction must be continued as necessary to prevent, drifting Since the airspeed decreases as the roundout progresses, the flight controls gradually become less effective; as a result, the crosswind correction being held would become inadequate. When using, the wing-low method then, it is necessary to gradually increase the deflection of the rudder and ailerons to maintain the proper amount of drift correction Do not level the wings; keep the upwind wing down throughout the roundout. If the wings are leveled, the airplane will begin drifting and the touchdown will occur while drifting. Remember, the primary objective is to land the airplane without subjecting it to any side loads which result from touching down while drifting and to prevent ground looping while the landing is being accomplished.

Crosswind Touchdown

If the crab method of drift correction has been used throughout the final approach and roundout, the crab must be removed the instant before touchdown by applying rudder to align the airplane’s longitudinal axis with its direction of movement. This requires timely and accurate action. Failure to accomplish this results in severe sideloads being imposed on the landing gear and imparts ground looping tendencies. If the wing-low method is used, the crosswind correction (aileron into the wind and opposite rudder) should be maintained throughout the roundout, and the touchdown made on the upwind main wheel. As the forward momentum decreases after initial contact, the weight of the airplane will cause the downwind main wheel to gradually settle onto the runway.

Crosswind After-Landing Roll

Particularly during the after-landing roll. special attention must be given to maintaining directional control by use of rudder, or nosewheel/tailwheel steering, while keeping the upwind wing from rising by use of aileron. When an airplane is airborne it moves with the air mass in which it is flying regardless of the airplane’s heading and speed. However, when an airplane is on the ground it is unable to move with the air mass (crosswind) because of the resistance created by ground friction on the wheels. Characteristically, an airplane has a greater profile or side area, behind the main landing gear than forward of it. With the main wheels acting as a pivot point, and the greater surface area exposed to the crosswind behind that pivot point, the airplane will tend to turn or "weathervane" into the wind. Wind acting on an airplane during crosswind landings is the result of two factors, one is the natural wind which acts in the direction the air mass is traveling, while the other is induced by the movement of the airplane and acts parallel to the direction of movement. Consequently. a crosswind has a headwind component acting along the airplane’s ground track and a crosswind component acting 90° to its track. The resultant or relative wind, then, is somewhere between the two components. As the airplane’s forward speed decreases during the after-landing roll, the headwind component decreases and the relative wind has more of a crosswind component. The greater the crosswind component the more difficult it is to prevent weathervaning. The headwind component and the crosswind component can be determined by reference to Figure 9-14. For example: a relative wind at 20 knots at an angle of 60 degrees to the runway has a headwind component of 10 knots and a 90 degree crosswind component of 18 knots. Federal Aviation Regulations require that all airplanes, type-certificated since 1962, have safe ground handling characteristics with a 90 degree crosswind component equal to 0.2 Vso. Thus, an airplane that stalls at 55 knots in the landing configuration, must have no uncontrollable ground looping tendencies with a 90° crosswind component of 11 knots (0.2 x 55). It is imperative that pilots determine the maximum crosswind component of each airplane they fly, and avoid operations in wind conditions that exceed the capability of the aircraft. While the, airplane is decelerating during the after landing roll, more and more aileron must be applied to keep the upwind wing from rising. Since the airplane is slowing down there is less airflow around the aileron, and they become less effective. At the same time the relative wind is becoming more of a crosswind and exerting, a greater lifting force on the upwind wing. Consequently when the airplane is coming to a stop the aileron control must be held fully toward the wind.

The 1999 Aviation Safety Program Maintenance Technician Awards has come to an end. The awards are given to individuals who complete one of the five different levels of continuing education in the aviation maintenance field. I doubt if any of us can say that we have an unlimited amount of surplus time on our hands. Training takes time; time is money. The following dedicated individuals and companies are being recognized for taking the time to improve their skills and thereby promote aviation safety through education.

It would be a great injustice not to mention four maintenance organizations in our district which demonstrated superior support for the Aviation Maintenance Technician training program. The highest level a company can reach for promoting recurrent maintenance training is the "Diamond Award". This year’s recipients of the Corporate Diamond Award are Woodland Aviation at Yolo County Airport, Clarksburg Air Repair of Clarksburg (and now Sacramento too), The Gryo House in Auburn, and IASCO in Napa. The program’s success would not be possible without special efforts from individuals within these companies. A special "thanks for a job well done" goes out to Richard Anderson of the Gyro House, Mike Pavao of Clarksburg Air Repair, Michael Mackes of Woodland Aviation, and Richard Darrimon of IASCO. IASCO is one of the few companies nationwide that can be proud of the fact that of 100% their eligible technicians received individual training awards. The FAA truly values such support, which starts at upper management and continues systemically throughout the entire company.