‘One of the most demanding manoeuvres in aviation’ — How pilots manage crosswind landings
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Nothing gives a pilot greater job satisfaction than a good crosswind landing. Dropping out the bottom of the cloud on a windy day and seeing the runway out of the side window really gets the heart rate going and the adrenaline pumping.
That said, a good crosswind landing takes more than just judgement and luck. It takes extreme concentration, skill and teamwork to complete one of the most demanding manoeuvres in aviation. This is your guide to how we deal with crosswinds.
Why we land with a crosswind
Aircraft fly not because of the engines but because of lift generated by air flowing over the wings. They provide the forward thrust to get the air flowing over the wings in the first place. For a basic example, if we need air to be passing over the wing at 100 mph to fly, we need to be moving forward at 100 mph to generate that lift.
However, if there is a 50 mph headwind, we already have 50 mph of the required 100 mph air over the wings needed to fly. As a result, we only need to be moving forwards at 50mph. Taken to an extreme, if the wind was 100 mph, we wouldn’t need to move forwards at all — we’d just be able to take off on the spot.
Conversely, if the 50 mph wind is coming from behind us, a tailwind, we start with minus 50 mph of air over the wings. As a result, we will need to travel forwards at 150 mph in order to achieve the required lift to get airborne. Not an ideal situation and exactly the reason why we prefer to take off and land into the wind.
However, even though runways are normally built in the direction of the prevailing wind, the weather doesn’t always play ball. For example, at London Heathrow, the runways are aligned in an east/west configuration as the wind in the south of the U.K. predominantly blows from the west.
Yet, as we all know, the weather changes day by day and, as a result, the wind doesn’t always blow directly down the runway. More often than not, it is coming at an angle to the runway and, at times, it blows directly across. As we are not able to change the direction of the runway, we have to accept the wind blowing across it. At any time there’s an element of wind from either side, it’s known as a crosswind.
That said, the effects of a crosswind vary depending on the airport and, more specifically, the runways available. At Heathrow, there are only two runways, so if the wind is straight out of the north or the south, we have no choice but to land with a crosswind. However, other airports often have a combination of runways. Boston Logan International airport has a combination of runways that enable pilots to land with as little a crosswind as possible.
What are the challenges?
On days where there is a considerable crosswind, we really have to bring our A-game. On a “normal” day where there is no wind or we are flying directly into the wind on landing, we can see the runway straight ahead of us as we make the approach. On a clear day, we can see the runway from more than 15 miles away. However, when there is a crosswind, we have to adapt how we fly the aircraft.
If there is a strong wind blowing from the right-hand side, if we point the nose of the aircraft straight at the runway, the wind will blow us off course and we will drift to the left of our path towards the touchdown point. To counter this effect, we have to point the nose slightly into the wind. The stronger the wind, the more we have to point the nose into the wind. As a result, the aircraft flies at an angle towards the runway, very much like a crab walk across a beach so this is technique is known as “crabbing.”
With an extreme crosswind, the crab angle can be so great that the runway, instead of appearing in the middle of our windshield, can be over to one side. It can sometimes feel as if we are looking along our shoulder to keep the runway in sight. The video below clearly shows the pilots aiming the nose of the aircraft to the left of the runway to compensate for a strong crosswind.
However, it’s not only the direction of the wind that keeps us on our toes, as the strength of the wind also makes a big difference. Understandably, the stronger the wind, the greater the effect it has on the aircraft. When a strong wind blows perpendicular to the runway direction, then our skills are really tested. What makes things more challenging is the fact that the wind is rarely a constant speed.
Gusts create sudden fluctuations in the wind speed, rapidly increasing or decreasing the airflow over the wings. As mentioned earlier, it’s this airflow that generates the lift. If the wind speed suddenly increases, extra lift is generated and the aircraft can get high on the approach. If the wind speed suddenly drops, lift is lost and the aircraft will sink. This is what causes the turbulence on windy days.
To add a third element, each time the gusts increase or decrease, the amount of crab angle we have to fly to keep lined up with the runway changes. As a result, we are intently focused on the flight path of the aircraft, ensuring that we keep it flying safely towards the runway at all times.
Commercial aviation is all about safety and, as a result, there are limitations to the crosswind that not only the aircraft can land in, but also which the pilots are allowed to do.
As part of the testing process for all new aircraft, the manufacturers take it to a part of the world where strong winds are commonplace. This includes places such as northern Canada and, like in the video below, Iceland. The test pilots fly numerous approaches onto a runway that gives them the strongest crosswind possible in order to see how the aircraft handles and to determine what the maximum crosswind limitation should be for the aircraft. For example, on the 787 shown in the video, the maximum crosswind it is allowed to land with is 40 knots (45 mph).
However, it’s not as straightforward as this.
When driving on a road, a car handles quite differently depending on if the road is dry, wet or icy. When driving on snow, we would naturally go around corners at a slower speed — and it’s the same for aircraft. When landing with a crosswind, at the moment of touchdown we want to ensure that we are able to safely control the direction of the aircraft. The last thing we want is to have flown a beautiful approach, only to slide off the side of the runway due to a combination of the strong winds and slippery surface.
As a result, the more slippery the runway, the lower the crosswind limit is.
In order to check this figure, first, we must ascertain how slippery the runway is. To do this we use a table published by the International Civil Aviation Authority (ICAO) known as a Runway Condition Assessment Matrix (RCAM), as seen here (PDF).
ATC passes us the runway surface description and from that, we can deduce the Runway Condition Code. We then take this number to the manual for the type of aircraft we are flying to find out the crosswind limit for the given runway condition. For example, on the 787, with a Runway Condition Code (RCC) of 6, the crosswind limit is 40 knots. However, if the RCC is 1, the limit drops to just 15 knots — a significant difference.
In addition to the aircraft limits, most airlines will impose limits on the crew, too. For example, an inexperienced First Officer may only be allowed to landing with a crosswind of one-third the maximum for the conditions, whereas an experienced First Officer may be allowed to land with the wind two-thirds of the limit. Anything above those, up to the maximum limit, the captain must do the landing. Even the autopilot is limited to just 25 knots of crosswind, so when it gets really windy, it’s only the pilots who can carry out the landing.
Crosswind landing techniques
Flying the approach in a crosswind, as already mentioned, is a question of crabbing the aircraft into the wind to ensure that it tracks directly towards the runway. However, once at this stage, we have a problem. With the nose still pointing off to one side as we pass over the threshold of the runway at 50 feet, we somehow need to get it pointing down the runway, without being blown off the side. This is where the real skill comes in.
Each manufacturer publishes approved techniques for touching down in a crosswind for a particular aircraft type. What may not be allowed on one type of aircraft may well be approved on another type. On the 787, Boeing has approved three techniques: de-crab during the flare, touchdown in crab and sideslip.
Personally, in my six years of flying the 787, I’ve never seen anyone use the sideslip technique due to its complexity. For the most part, people tend to use a combination of the de-crab during the flare and touchdown in crab techniques.
The objective of the de-crab in the flare technique is to keep the wings level all the way down, flare the aircraft (the bit where we raise the nose just before touchdown) and then touchdown on the runway. Keeping the wings level reduces the chances of scrapping an engine on the runway and by de-crabbing during the flare, the nose is pointing down the runway making it more comfortable for the passengers.
As we approach 30 feet, we start to pull back on the control column as in a normal flare. This leaves just a few seconds to get the nose lined up with the runway and to do this, we use our feet on the rudder pedals. If the nose of the aircraft is pointing off to the left of the runway, a gentle squeeze of the right rudder will bring it round to line up with the runway, ready for touchdown. However, there’s one final twist.
As we squeeze the rudder to swing the nose to the right, it results in the left-wing moving through the air fractionally faster than the right-wing. If we remember from earlier, this added speed results in greater lift. So, if we’re not expecting it, can result in the left wing rising and the aircraft fling off to the right-hand side of the runway. The counteract this, as we squeeze in the right-rudder, we also turn the control column slight to the left to keep that left wing from rising.
So, in the final few moments before touchdown, we are pulling back on the controls — just enough to slow the rate of descent, squeezing the rudder with a foot; just enough to line the nose up with the runway and turning the control column to one side; and just enough to stop the wing from rising. And this is all done at 160 mph. The target is to touch down firmly in the correct part of the runway to ensure that the brakes take effect as quickly as possible — a good crosswind landing is one that you feel.
The result of all this is demonstrated perfectly in the video below.
Most pilots love a crosswind landing because it gives us a chance to demonstrate the skills that we rarely get to showcase. The satisfaction from performing a textbook crosswind landing is probably the best part of the job. It takes extreme concentration, skill and teamwork to complete a safe crosswind landing, something that we practice regularly in the simulator. So next time you find yourself landing in a storm, rest assured that your pilots are up to the job and probably enjoying every second of it.
Featured photo by JMF de Almeida/Getty Images.
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