Thousands watching LHR live; How pilots are dealing with the challenging conditions landing in London today
We're well into winter storm season. As you've likely seen on social media, London is dealing with major winds right now making for a fascinating look at how planes land in high winds with the arrival of Storm Eunice. Hundreds of thousands of people are watching a live stream on Youtube of London's Heathrow Airport at Big Jet TV.
Forecasters have predicted 100mph winds for Wales, and many other parts of the country can expect to see winds into the 80s and 90mphs. Along with this will come heavy rain and the travel disruptions this kind of weather brings.
However, one mode of transport is even more at the mercy of the weather: flying.
For more TPG news delivered each morning to your inbox, sign up for our daily newsletter.
On the ground
The problems with strong winds start even before the aircraft has left the gate. The ramp area around a parked aircraft is a very busy and potentially dangerous place. With a variety of service vehicles required to help prepare the aircraft for its next flight, there are plenty of chances for a collision, so everyone working on the ramp has to remain careful and vigilant at all times.
However, it can become even more dangerous when the wind starts to pick up. Many items and structures on the ramp are not particularly aerodynamic and can be quickly affected by a rise in wind speed.
Sets of steps can blow over, baggage containers can move and other small objects, such as cones, steps, etc., can blow onto taxiways and runways. As a result, ground staff has set procedures that they must follow to ensure that these items do not become a threat to themselves or the aircraft.
This will normally include adding extra chocks to the aircraft to ensure that it doesn't move, removing safety cones from around the aircraft and making sure that there is no FOD (foreign object debris) left around the aircraft. They will also ensure that baggage containers are tied down and baggage trolleys have their brakes applied.
As the forecast windspeed increases, more steps have to be taken. This could include moving all ground equipment into the shelter of a building and stopping the use of steps and high lifts. All aircraft types also have a wind limit on the operation of the doors, both cabin and cargo. On the 787, this is 40kts (73kmh/45mph). Beyond this, the doors should not be operated as it risks damaging the movement mechanism.
The result of all this could mean that the ground servicing of an aircraft is severely restricted and quite possibly stopped altogether. Aircraft may arrive at the gate but not be able to open the doors for baggage to be unloaded or catering trucks may not be able to access the cabin to restock the gallies for the next flight.
All this ultimately leads to delays.
Whilst the wind is causing problems on the ramp, up in the calm of the flight deck, the pilots are preparing for departure and focusing their minds on the challenges that strong winds bring. In fact, our focus on this task will have begun hours earlier as we made our way into work.
Like a sailor continually assessing the ocean, a pilot always assesses the weather. Seeing how the wind is behaving, what clouds are forming and how this could affect their flight. The commute to work is a good way to get a feel for the conditions. We'll take note of the wind direction and strength, how gusty that wind is, how much moisture there is on the ground and how the cloud cover is around the airport.
Many staff car parks give a good view of the runways so we can see how the weather conditions are affecting aircraft as they are taking off and landing. Are they experiencing any sudden gusts on landing? How are the flight conditions just after takeoff? All the while, we are building up our mental model of how the weather will affect our flight in a couple of hours.
The design of major international airports is not by mistake. Knowing the prevailing wind direction, runways are constructed in a direction that will result in the wind blowing as close to straight down the runway on most days a year. Not only does this shelp with the performance of the aircraft, but it also makes life a little easier for the pilots.
However, when winter storms such as Eunice hit the U.K., the wind is rarely straight down the runway. The more the wind blows across the runway, the more it affects how the aircraft handles on the takeoff run.
The aircraft's vertical tail is a key component in keeping the aircraft stable in the air. Without the tail, as the aircraft flew through the air, it would wobble about laterally, making it difficult for the pilots to control and incredibly uncomfortable for the passengers. By fitting the tail, it acts like the keel of a boat, keeping it stable in the air.
However, an element of this stability comes from the length of the fuselage. The longer the fuselage in relation to its width, the more stable the aircraft is. Conversely, the shorter the fuselage compared to its width, the more unstable it is. As a result, an aircraft such as the A340 -- with a long and thin fuselage -- has a relatively short tail, but the A380, with a short, fat body, has a particularly large tail.
Whilst the bigger tail brings more stability, it also acts as a huge weathercock in crosswind conditions.
As the wind hits the tail, it pushes it across the runway, causing the nose to turn in the opposite direction. To counter this, pilots must use the pedals under their feet to control the tail rudder. This counteracts the effects of the wind.
However, this input also creates a secondary effect.
As the input of the rudder in effect drives the windward wing (the left-wing in the image above) into the air more quickly, it generates more lift than the other wing. Left uncorrected, this could cause the right-wing to drop just as the aircraft lifts off, striking the engine or wingtip on the ground.
How this is countered depends on the aircraft type and each manufacturer details the best way for pilots to fly the aircraft in these conditions.
On Boeing types, such as the 787, as we accelerate down the runway, we must gradually turn the control wheel towards the side the wind is coming from. This deflects the control surfaces on the wing, countering the effect of the extra lift.
Once airborne, we release the input on the rudder and allow the aircraft to fly 'side-on' in a position known as "crabbing". This entails pointing the nose toward the wind to ensure that we fly the correct track over the ground.
Boundary layer turbulence
Once airborne, the fun is still not over as it is here where the real effects of the wind can be felt. During the takeoff run, passengers may well feel the aircraft jolting and swinging as gusts of wind hit the aircraft, requiring the pilots to adjust their control. If sitting at the back of the aircraft under the tail, this can feel quite dramatic at times.
However, once airborne, there is another element that comes into play: the boundary layer.
The air around us behaves like a liquid. It will flow from an area of high pressure to an area of low pressure and this is what we experience as wind. When the differences in pressure are very high in a short geographical distance, the airflow (windspeed) is high -- very much like a river flowing down a mountainside.
When the water flowing in a river hits obstacles, such as rocks, bridges and stray tree branches, the flow is disrupted and it becomes turbulent. The same happens with the wind.
Up in the atmosphere, the wind flows unimpeded and so the air, for the most part, is smooth. However, the closer to the ground it gets, the more obstacles there are such as hills, office blocks, houses and trees. This is known as the boundary layer. As the air hits these obstructions, it becomes turbulent and the stronger the wind, the more turbulent that air becomes.
As a result, on days like this weekend when the wind is forecast to reach 80–100mph, the turbulence created in the boundary layer can be extreme. Fortunately, this is never dangerous, only uncomfortable. The aircraft is more than capable of dealing with the worst of this turbulence, no matter how bad it may feel.
We will normally instruct the cabin crew to stay in their seats until we tell them that it is safe to move around. If possible, we will try to climb to a higher altitude more quickly, to escape the effects of the boundary layer quickly.
Once up in the air and away from the boundary layer, conditions start to smooth out. However, what about aircraft landing in strong winds?
Like when arriving into work on a windy day, the preparation for landing in windy conditions will have begun many hours before the pilots even begin their descent. Before leaving the departure airport, we always study the weather forecasts for our arrival time. The potential of strong winds will always get our attention.
As mentioned above, with strong winds often come delays. With that in mind, time in hand is always our friend so these are not days to take the minimum required amount of fuel for the flight.
Delays due to strong winds occur for a whole host of reasons. Parking stands may get backlogged as aircraft are unable to depart due to ground restrictions. Without any parking spaces on the ground for arriving aircraft, they must wait in the air until such time there is space.
The rate at which aircraft can land is also reduced during times of strong winds. On a normal day, an airport like Heathrow may land around 45 flights an hour for every hour throughout the day. This relies on the aircraft maintaining a certain speed over the ground during the approach to ensure that this number is met.
However, with strong winds, this can be severely affected. Why?
Aircraft fly because of the air flowing over the wings. It is why the engines merely provide the forward thrust to drive the wing through the air, creating lift. In this example, let's assume that an aircraft needs to have 180mph of airflow over the wings to fly. On a day with no wind, the aircraft will have to fly through the air at 180mph to generate that lift. By virtue of this, its speed over the ground is also 180mph.
However, if the aircraft is flying into an 80mph headwind, it will only need to be moving forwards at 100mph to create the same lift, meaning that it is only flying over the ground at 100mph. This means that it will take a longer time to travel the same distance down the approach, resulting in fewer aircraft landing per hour.
This creates a backlog in the sky which requires us to carry more fuel whilst we wait for our turn to land.
That said, Heathrow now uses a system called Time Based Separation that can reduce these delays by up to 60%, saving around 15,000 tons of fuel.
Go-arounds and diversions
Strong winds go hand-in-hand with the increased likelihood of a go-around or rejected landing. Touching down safely in strong winds can be particularly challenging, so we never back ourselves into a corner. We always ensure that we have an 'escape' plan and this is via a go-around or rejected landing.
If at any point during the approach the pilots are not happy with how things are going, they can apply full power to the engines and go back up to a safe altitude before deciding on what their next steps will be. It is far safer to do this than to continue with a landing that may result in the aircraft touching down in an unsafe manner.
Even if the aircraft has touched down, until the point where the reverse thrust has been engaged, the pilots can still go back up into the air with a slightly different maneuver called a rejected landing, as demonstrated perfectly in the video below.
The footage may look dramatic but the aircraft (particularly the landing gear) is built to withstand such impacts and the crew executed the perfect rejected landing after a gust of wind caught the aircraft at the last moment before touchdown.
Once back up in the safety of the air, the pilots then have time to make a decision on what to do next. The more fuel they have at this point, the more time and options they will have available to them.
Ultimately, if the weather conditions do not improve, they may have to divert to an airport where the weather is more favorable -- something that they will have thought about many hours previously when they decided on how much fuel to carry for the trip.
Strong winds do cause challenges for pilots and ground staff, but they are nothing that is ever considered dangerous. Every six months, pilots practice these exact maneuvers in the safety of a flight simulator to ensure that, should the conditions arise for real, they are well prepared and able to deal with them.
In these conditions, safety is key. Safety for those on board the aircraft and also for those working on the ramp. As a result, delays, cancellations and diversions will occur but these decisions are not taken lightly. Ultimately, if it is not safe to depart or to land, the crew in charge of the aircraft will make that decision and stick with it.
Punctuality is important but not nearly as important as safety.