It was one of those early spring days when the lows were very low, the high pressures very high, and in between the wind was howling. As is often the case on these days, the sky was clear and the flying conditions good—until it was time to land.
I was waiting my turn to go on runway 16 at Chicago Executive—the place many of we old timers still call Palwaukee—and the wind was blowing from 250 degrees at 22 knots, with gusts to 32 knots. In other words, it was exactly a direct crosswind. Ninety degrees to runway 16-34, the main runway, and the only runway realistically usable by turbine airplanes.
Pilots of the piston airplanes were wisely waiting out the blow so I got to watch a parade of bizjet pilots tackle the crosswind velocity that was near or above the demonstrated—but must always add not limiting—capability of their airplanes.
Each pilot was carrying a huge crab into the wind down final approach. And the air was bouncy, so wings were dipping up and down. And no doubt the indicated airspeed was bouncing around. Reports of gains and losses of five to 10 knots airspeed on final were common.
As each pilot descended close to the pavement they attempted a de-crab maneuver by lowering the upwind wing, or in some instances simply ruddering the nose away from the wind with the wings more or less level.
Tires smoked at touchdown, and the airplane noses jerked back toward the centerline. Despite a crosswind at the limits, nobody that I watched came close to having serious control problems after touchdown.
We’ve all seen this movie before on countless videos of airline pilots attempting to land in extreme crosswinds. Sometimes the wind wins and the crew goes around when they can’t stop the drift. But more often than not, the amateur videographer captures the jet touching down in a significant crab angle to the runway, tires smoking, and the airplane nose pivoting back toward the runway centerline.
How is it possible to land in such extreme conditions? There are several factors that matter, but the most important is that the pilots are holding a track over the ground that aligns with the runway centerline. It’s not where the airplane is pointed but where it is going, where the mass of the machine is traveling, that allows it to remain on the runway after touchdown.
In little airplanes we are taught that in crosswind landings using the aileron and rudder to align the nose of the airplane with the runway centerline is essential. And if conditions allow that, it’s an excellent and predictable landing technique.
But when the breeze is up, keeping the nose pointed exactly at the far end of the runway can be difficult—and at some wind velocity, impossible—and the airplane will slide downwind. And when that happens, it’s pretty much game over for a predictable landing because the airplane will touch moving sideways which means its mass, its energy, will be heading off the runway instead of down the runway.
The essential technique is to keep the airplane tracking over the centerline, even when that requires a crab into the wind. If the airplane track is true to the centerline, the inevitable swerving after touchdown can be controllable because the momentum of the airplane is down the centerline.
With tricycle landing gear the center of mass of the airplane is ahead of the main gear. That means when the airplane touches in a crab the momentum will pull the airplane back toward its direction of travel. Its ground track, in other words. If that track had been down the centerline, the momentum wants to continue down that path.
Of course, once the airplane is on its wheels the crosswind isn’t done with its evil efforts. The airplane is really a weathervane so the wind is going to push the tail away from the wind direction. Opposite rudder is the solution, but rudder authority is limited, especially as the airspeed slows. That leaves nosewheel traction and some differential braking as the tools to keep the airplane tracking straight on the rollout.
Jets have several distinct advantages over piston airplanes in this regard. For one, jets sit on their gear at a negative angle of attack so when the nose comes down the lift is gone and the tires—most importantly the nosewheel—can grab the pavement. Light airplanes sit on their gear at a very neutral angle of attack, or perhaps even a little positive (nose up) in some models. That means the wing still is producing some lift after touchdown, robbing the tires of needed traction for control.
Another great crosswind landing advantage in jets are spoilers. When the airplane touches, the spoilers pop out, killing nearly all lift and planting the airplane on its gear. In light airplanes it’s easy to bounce, at least a little, and that requires yet another fight for control to keep the airplane tracking down the centerline.
And the wing loading in jets is many times higher than in a piston airplane. That means gusts of the same strength simply can’t displace the heavier airplane as much, no matter how good or quick a light airplane pilot is on the controls.
If you’re flying a taildragger, forget everything above. Taildraggers really need to touch down with the longitudinal axis aligned with the centerline and not in a crab. The reason is the center of mass is located aft of the main gear in a taildragger, so the momentum after touching in a crab will try to carry the tail beyond the nose. A ground loop, in other words.
So for those of us flying nosedraggers on windy days, remember it’s tracking the centerline that matters most. If you maintain that track the touchdown and rollout can be a thrill, but you and your airplane can handle more crosswind that you may expect.