Flying with world leaders: How pilots land big aircraft into small airfields
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This week, President Biden made his first trip to the U.K. for the G7 Summit, making the transatlantic journey in his modified Boeing 747 with the callsign Air Force One. The aircraft departed from Joint Base Andrews in Maryland to RAF Mildenhall in Suffolk. After addressing American servicemen and women at the predominantly U.S. Air Force-used base, he then made a much shorter flight across the U.K. to Newquay Airport (NQY) in Cornwall.
It may come as a surprise that the small seaside town of Newquay has an airport. It may come as an even bigger surprise that an aircraft as large as a 747, normally associated with large international airports such as London Heathrow and New York John F. Kennedy, is able to land there. Well, despite its small name and passenger terminal, the runway at Newquay Airport is much bigger than you’d expect — and this is due to its history as a military airfield.
Named RAF St. Mawgan in 1943, the airfield was upgraded by the U.S. Air Force during World War II, further expanding the main runway. Over the post-war years, the airfield saw fewer military traffic and more civilian aircraft, and in 2008, Newquay Airport was handed over to Cornwall Council, which began the process of turning the airfield into a predominantly civilian airport.
So, how much runway do pilots need to land? And, especially when we’re talking about transporting some of the world’s leaders, how do pilots ensure that the large aircraft have space enough to land? Let’s take a look.
How much runway do we need?
Before landing any aircraft — be it a two-seater Cessna or a giant Boeing 747 — the pilots must satisfy themselves that the runway is long enough for them to stop safely. However, this isn’t as straightforward as a single figure for each aircraft type, as the required landing distance will be different for every single flight.
Related: How do aircraft brakes work?
Landing Distance Available
Each runway we land on has a published Landing Distance Available, the LDA. However, this isn’t always the same as the total length of concrete. Some runways, like Runway 30 at Newquay, have what is known as a displaced threshold. This means that we are unable to use the full length of the runway for landing, normally due to an obstruction in the approach path. As a result, we must touchdown further down the runway, as shown in the image below.
This means that the LDA on Runway 30 is 2,444 metres, whereas if we were to land from the other end on Runway 12, the LDA is 2,637 metres, as we are able to use the full length of the runway for the rollout after we touch down.
Required Landing Distance
Landing distance is defined as “the horizontal distance traversed by the aeroplane from a point on the approach path at a selected height above the landing surface to the point on the landing surface at which the aeroplane comes to a complete stop.” Quite the mouthful.
In plain English, this means the distance required from passing over the start of the runway (at 50 feet) to becoming stationary. This is also known as the calculated landing distance.
However, as this is the minimum distance calculated for a textbook landing, most airlines use a safety factor of 5% to 15% on top of this. This ensures that should the landing not be perfect — for example, if the aircraft touches down a little deeper than planned — there is still sufficient runway remaining. This is known as the Required Landing Distance.
Therefore, in all cases, the landing distance available must be greater than the required landing distance.
The Required Landing Distance will vary depending on a number of environmental factors, including how slippery the runway is, the wind speed and direction, the outside air temperature and air pressure. It will also be affected by the aircraft weight, the flap setting used, the autobrake setting used and reverse thrust.
Landing distance calculations
Many older aircraft require the pilots to use complicated tables with multiple rows and columns to collate all the above factors and work out the Required Landing Distance. At times of high workload and reduced personal performance from tiredness, just the smallest mistake can result in an erroneous calculation. When runways are short, this can prove fatal. To help combat this threat, the 787 Dreamliner has the Onboard Performance Tool (OPT).
Using this computer, pilots enter all the relevant information as seen in the image below. The OPT then calculates the distance required. Not only does it reduce potential errors, but it also allows pilots to quickly carry out a new calculation if the reported wind or runway in use changes. With some very short runways around the world, a shift in the wind could make all the difference between landing safely and going off the end of the runway.
In the example above, the Required Landing Distance is 2,311 metres with an LDA of 3,356 metres meaning that there is plenty of runway available for us to land safely. However, other runways are not quite as generous.
In certain conditions, the Required Landing Distance may only be 100 metres less than the LDA. As a result, there is very little margin for error. In these situations, it is absolutely key that we touch down in the correct spot and get all the retardation devices working as soon as possible.
That said, we don’t aim to touchdown right at the start of the paved surface. The landing distance calculation assumes that we pass over this point 50 feet above the ground and shortly after we start the flare — the action of gently raising the nose and reducing the rate of descent in anticipation of touching down.
Now, all pilots love pulling off a smooth landing, and on a nice long runway, we have a little more concrete to play with to extend the flare a little and make this happen. However, do this on a short runway and there’s a very real risk that you may go off the end. As a result, a good landing is one where we touch down firmly on the aiming point, putting the full weight of the aircraft on the wheels as soon as possible and letting the brakes do their work. It may not be as comfortable for the passengers, but it’s far more comfortable than going off the end of the runway.
Ways to reduce the landing distance
All this is fine if the landing distance calculation comes out with a satisfactory number lower than the LDA. But what if that number is greater than the LDA? We have a problem.
We can’t change the length of the runway (unless we divert to another airfield), and the environmental conditions don’t often change so quickly that they can be considered a solution. Whilst we can’t change the conditions outside the aircraft, there are a number of factors that we can change inside the aircraft to help reduce our required landing distance.
Use more flap
In preparation for landing, we extended the slats on the leading edge of the wing and the flaps on the trailing edge of the wing. These increase the surface area of the wing, increasing lift and allowing us to fly at slower speeds. However, the more flap you extend, the greater the aerodynamic drag. The greater the drag, the more engine power is needed and the more fuel is used. It also increases aircraft noise.
Most commercial airliners have a range of flap setting permitted for landing, depending on the level of drag desired. On the 787, Flap 25 is the setting most commonly used on longer runways as the higher touchdown speed gives a good compromise between lift and drag. However, the faster we touch down, the greater the landing distance. If we can reduce the landing speed, we can then reduce the landing distance.
To do this, we select a greater flap setting (Flap 30 on the 787) increasing the lift generated, allowing us to fly at a slower speed. Yes, this is less efficient but it’s far more efficient than diverting to another airfield.
Use a higher autobrake setting
The wheel brakes are controlled using the top of the rudder pedals under our feet. To use them, we slide our feet up the pedals and push on the top with our toes. This is pretty easy to do when taxiing the aircraft on the ground, but just after landing, especially in a strong crosswind, it can be tricky to get your feet into the correct position. By the time you do, hundreds of metres of the runway may have already passed behind the aircraft.
The autobrake pretty much does what it says on the tin. When the main wheels touchdown on the runway, the brakes automatically engage and produce a set deceleration for the autobrake setting selected. Not only does this prevent runway distance from being wasted, but it also ensures that the brakes are applied evenly.
On a longer runway, we aim to use an autobrake setting that is comfortable for the passengers whilst enabling us to vacate the runway at a convenient location. However, on a shorter runway, this isn’t always possible. Using the OPT, we can increase the autobrake setting and see how it affects the landing distance until we reach a value that is less than the LDA.
Landing into a short runway provides serious challenges for pilots. With reduced concrete available, there is a reduced margin for error. As a result, it’s imperative that we get the aircraft down firmly and get the brakes slowing the aircraft quickly, even if it is uncomfortable for the passengers.
Even if the runway initially seems too short, there are a few things that we can do to reduce our required landing distance. Increasing the flap setting allows us to fly slower and increasing the autobrake setting makes the brakes work harder.
Ultimately, a safe landing is what we are trying to achieve. Even though it may seem sporting, done correctly, a short runway is no more dangerous than a longer one.
Featured photo courtesy of Newquay Airport.
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