In recent weeks we experienced an uncommon and unwelcome pattern of cold air masses in the Midwest that not only brought winter-like temperatures, but also strong frontal boundaries with gusty winds and accompanying low-level wind shear (the PIREPs were plentiful to prove it). Needless to say, the flying conditions have been less than ideal and have put crosswind competency to the test. Several consecutive flights with wind gusts and crosswind components at or near the airplane and pilot limits, have me longing for a flight with a few knots of wind straight down the runway.
Being based at an airport absent the luxury of a crosswind runway, you’re forced to maintain a certain degree of crosswind proficiency. But if you’re a pilot who often has many choices of runways most aligned with the wind, or chooses to avoid crosswinds altogether, these situations demand careful consideration lest the crosswind conditions become perilous.
Despite considerable experience in the aircraft I was operating and years of practice in crosswind conditions at my home base, as part of my safety management strategy, I have still have pre-determined limitations for total wind gust (gust factor) as well as total crosswind component. Establishing these personal limitations effectively eliminates the external factors that could cloud my judgement on a particular flight. In other words, the decision to attempt a landing versus seeking an alternate airport has been largely made on my behalf by virtue of the conditions being reported. An ancillary benefit is that passengers also understand this basic premise that policy (designed to enhance safety) may prevent an attempt at a takeoff or landing under certain conditions.
While crosswind considerations and the resulting personal limitations tend to focus largely on landing, crosswind takeoffs also warrant equal analysis. Consider that a) the same aerodynamic forces and control limits are at play during a takeoff as they are with landing and b) it’s prudent to have the airport you’re departing available for landing in case an immediate return is required.
When departing with a crosswind, position the ailerons into the wind. By raising the aileron on the upwind wing, we impose a downward force on the wing to counteract the lifting force of the crosswind.
To begin the takeoff, full aileron input should be held into the wind. As speed builds, this control input can be relaxed as the control surfaces become more effective and the crosswind effects less pronounced (as the relative wind changes). As with a normal takeoff, rudder pressure will also be used to maintain directional control. Keep in mind that the airplane will have a natural tendency to weathervane into the wind so anticipate additional downwind rudder pressure to maintain a straight ground track.
At liftoff, the proper technique is to sideslip the airplane (maintain the longitudinal axis of the airplane parallel to the runway) in case the airplane were to settle back to the ground. In a sideslip, continue to position the ailerons into the wind to keep the upwind wing from rising and prevent drift off of the runway centerline. Utilize rudder pressure to prevent weathervaning and to keep the longitudinal axis parallel to the runway.
If you were to immediately establish a wind correction angle and the airplane were to inadvertently settle back to the runway, dangerous side loads could be imposed on the landing gear and make directional control difficult if not impossible.
If gusty crosswinds exist, it would also be a prudent choice to hold the airplane on the ground slightly longer than in a normal takeoff setting if field conditions permit. This will allow for more positive control at liftoff and mitigate a sudden gust that may rob you of lift. After a positive rate of climb is established, you’ll want to transition from a sideslip to a wind correction angle that keeps the aircraft flight path tracking the runway centerline until departing the traffic pattern.
Once you’ve determined the crosswind conditions of the day are within your capability, it’s time to put good technique into practice. The most common technique is the crab method that transitions to a sideslip just before roundout. Essentially, the takeoff method just described in reverse.
During your stabilized final approach, a wind correction angle (crab) should be established into the wind so that the aircraft’s flight path is tracking the runway centerline. Keep in mind, the amount of this correction will vary during descent as speed and wind direction may shift with altitude. Just before the roundout, the aircraft should be transitioned from a crab to a sideslip so that the longitundinal axis of the airplane is once again, parallel with the runway. To effect the sideslip, position the ailerons into the wind to keep the upwind wing from rising and prevent drift off of the runway centerline. Utilize opposite rudder pressure to prevent weathervaning and to keep the longitudinal axis parallel to the runway.
The amount of control force necessary to maintain runway centerline with the longitunidal axis parallel for landing will vary throughout the roundout, flare and touchdown as control effectiveness and crosswind effects diminish with decreasing speed. If the proper technique is followed, touchdown should be made on the upwind main wheel first. It’s important at touchdown to maintain the crosswind technique to ensure positive control throughout the landing roll. After wheels down, continue to apply aileron pressure into the wind until reaching full aileron input nearing taxi speed.
It’s worth re-emphasizing that the proper crosswind technique will result in constantly changing control inputs and pressure to track the runway centerline and keep the aircraft’s longitudinal axis parallel with the runway. If the aircraft begins to drift, take immediate positive action to increase the amount of bank into the wind. Add corresponding opposite rudder pressure to keep the nose aligned and parallel with the runway.
Type certification requires that aircraft be tested and found to be controllable in a 90 degree crosswind up to a velocity of 20% of the aircraft’s stall speed in the power-off, landing configuration without the pilot possessing any extraordinary skill. In a Cessna 172, this would equate to about 10 knots (direct crosswind). Maximum demonstrated crosswind velocity is required to be published, and while it often exceeds certification requirements, a good rule of thumb is to stick with the more conservative estimate as a personal limitation.
Gusty wind conditions present yet another variable. In order to mitigate the risks associated with rapidly changing wind speed and corresponding effects on lift, it’s advisable to add a correction to your planned final approach speed. The widely accepted best practice is to add half the calculated gust factor to your final approach speed – the gust factor being the difference between the sustained wind and reported gust.
As an example, if winds were being reported from 250 at 10 knots gusting to 16 knots, the gust factor is 6 knots (16-10). Applying the half gust factor (3) correction would result in a final approach speed of 3 knots faster than your normal final approach speed.
This correction makes sense and is an effective mitigation strategy up to a certain point. But as your corrections increase, you’ll need to consider whether the higher approach speed and corresponding wind shear results in an equally dangerous situation.
It’s true that we never fully “master” the crosswind. We can only hope to learn and improve from our humbling experiences. But continuing our diligent practice in a controlled environment will equip us with the confidence and skill to manage those unexpected conditions and give us the flexibility to enjoy more flying days ahead.