How to land the largest passenger aircraft in the world!

Well it has been a while since I’ve put a blog post together. Sorry about that. I have been very busy with various projects including the videos which I hope you have seen and enjoyed. I have previously discussed how we get the A380 into the air, now comes the tricky bit….landing it.

A typical landing weight for the A380 is a quite remarkable 365-370 tonnes! To put that into context, that is only 30 or so tonnes below the maximum takeoff weight of a 747-400! However, due to the quite brilliant wing design, the final approach and landing speed of the A380 is actually quite low. Lower, in fact, than the 747, 767, 777, and 787. In a recently published notice by Air Traffic Control at Heathrow, they state their typical approach speed of an A380 to be 133 knots. By comparison the 777-300 approach speed is   stated as 143 knots and the 747-400 as 144 knots. This only adds to the appearance of the A380 flying so slowly near the ground.

We will start our approach around 20 miles from the runway. At this point we would normally be flying at 220 knots. The wing is designed for optimum performance at high speed. If we want to fly slower than around 200 knots we have to change the shape to make it more curved and add extra lift using slats on the leading edge and flaps on the trailing edge. These are the large surfaces you will see moving as we slow down to final approach speeds. There are 8 slat surfaces and 3 flap surfaces on each wing. In addition, the three ailerons also act as flaps in what is termed a droop function.

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At this point we would typically reduce our speed to 180 knots. In order to do this we check the airspeed is below the maximum speed for Flap 1, then move the flap lever on the centre console to the Flap 1 position. Unlike Boeing aircraft, which have flap settings which correspond to the angle of flap deployment, Airbus have gone with a simpler nomenclature of Flap 1, 2, 3, and Full. There is also a Flap 1+F position, but this cannot be directly selected. When we first reduce speed and select Flap 1, only the leading edge slats extend. When the speed drops below 205 knots the first stage of flaps automatically extends, resulting in the 1+F (flap) setting. This setting actually gives 20° of slats, 8° of flaps, and 5° of aileron droop. The table below gives the surface positions for each flap lever position.

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The speed of 180 knots is a typical speed at which we start down the glideslope to the runway. At busier airports, Air Traffic Control have to ensure aircraft do not get too close together on the approach, but also need to maintain a high flow rate for landing, so accurate speed control is essential. The next speed reduction will be to 160 knots. This requires further flap extension to configuration 2. We will typically hold this speed until 5 miles from the runway, at which time we will select the landing gear down, Flap 3, and start reducing to our final approach speed. The majority of landings are conducted at Flap FULL position, in order to minimise the approach speed. However, there are certain situations where we may wish to land using Flap 3 instead. This results in a slightly higher approach speed, but may be preferable if we are landing, for example, on a day where significant windshear has been reported on final approach and there is an increased possibility of having to perform a go-around. Flap 3 produces significantly less aerodynamic drag than Flap FULL, so the aircraft performance in a go-around would be better.

By 1000 feet above the airfield we will be established on the final approach with the undercarriage locked down, the flaps at landing position, at our final approach speed of around 135 knots. This is a mandatory requirement for safety reasons. We have to be fully set up for landing by 1000 feet above the runway. Now the fun part…Putting 370 tonnes of aircraft onto the runway in exactly the right place. Each runway has a touchdown zone. We MUST land within this touchdown zone. If it becomes obvious we are not going to land by the end of the touchdown zone we have to fly a go-around. This is because our landing performance is calculated based on us landing within the touchdown zone. If we were to land beyond the end of it there is a chance we would not have enough runway left to stop the aircraft. Unfortunately, over the years, there have been a number of accidents which have been caused by pilots not flying a go-around when they have ‘floated’ too far down the runway. Therefore, the British Airways Safe Landing Policy is explicit in allowing either pilot to call go-around if they consider the aircraft will not land in the right place. As always, safety is our number one concern.

But let’s get on with the practicalities of actually landing the aircraft. We will assume this is to be a manual landing, not an automatic one. The vast majority of landings are flown manually. Automatic landings are normally only carried out in foggy conditions. The landing pilot will have taken control of the aircraft just below 1000 feet. They will concentrating on keeping the aircraft flying down the extended centreline of the runway.  This is done by imagining the painted line running down the centre of the runway extending beyond the runway itself and coming straight at you. The idea is you keep that pointing straight at you by moving the aircraft left or right as appropriate. It is also essential to keep descending at the correct rate and following the 3 degree glideslope to the runway. This is done partly by reference to the flight instruments, but also by looking outside at the runway. All pilots have a mental image in their mind of how a runway should look, the perspective, and the angle. Over time it becomes automatic to manoeuvre the aircraft on the approach to maintain this visual image. The closer you get to the runway, the more time is spent looking out at it, with just the odd flick of the eyes back inside to look at the instruments to make sure all is ok.

This is the view from the flight deck at 500 feet above the landing runway….

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Continuing down the approach to 200 feet above the runway….

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The PAPIs (Precision Approach Path Indicator) lights are visible to the left of the runway. We should touch down next to these. If we are on the correct glideslope we will see two red lights and two white lights. More reds than white mean we are too low, and more white than red mean we are too high.

 

Now just 100 feet above the runway. PAPIs very clear. On the glideslope. Centreline of the runway pointing straight at us.

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At 100 feet above the runway the flight control laws change. Pitch trim is no longer automatic, and the previous pitch flight control law changes to a landing ‘flare’ law. This is a modified pitch law which provides smoother control, allowing precise control of vertical speed and touchdown point.

Now only 50 feet above the runway….

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At 50 feet above the runway, the flare law introduces an effect which produces a slight nose down tendency. This means the pilot has to start moving the control stick back during the landing manoeuvre, which is known as the flare. In normal conditions the flare height is 40 feet above the runway, but varies slightly due to operational conditions such as wind speed and direction. As we go into the landing the sequence of events is as follows:-

  • Start the flare with positive back pressure on the sidestick, raising the nose of the aircraft a couple of degrees, then hold the pitch attitude as you look down the end of the runway
  • Wait
  • At around 20 feet close the thrust levers. The aircraft has an automatic call out of ‘RETARD’ as a reminder. It may be necessary to close the thrust levers earlier or later than this depending on the weather conditions.
  • Keep looking down the end of the runway. Do not allow the aircraft to roll and if necessary use rudder to bring the nose of the aircraft left or right to point directly down the runway just before touchdown. This is called the ‘crabbing’ technique when there is a crosswind.
  • Wait for touchdown, making very minor corrections if required. DO NOT over-control.
  • At touchdown the ground spoilers extend to ‘dump’ the majority of the lift, putting weight onto the wheels as the automatic brakes activate.
  • Select reverse thrust as required, always a minimum of idle. The A380 only has reverse thrust on the inner engines.
  • Use the rudder pedals to keep the aircraft tracking the centreline of the runway.
  • Lower the nose gently without delaying touchdown. It must be flown onto the runway and there may be a slight pitch up tendency as the ground spoilers deploy.

 

Just before touchdown…….

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Congratulations! You have just landed 370 tonnes of A380 in Vancouver!

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I hope this has been an interesting introduction in how to land an A380. If you have any comments or questions please ask…..

 

Below is the video of our landing at Vancouver on runway 08L on 11th September 2017, from which the above still photos were extracted. I hope now you have read the above description you can see exactly what First Officer Jon Leggett was doing as he performed this perfect landing.

Stopping! All about brakes and BTV – Brake To Vacate

I hope you enjoyed the first blog post. Thank you to all those who sent feedback!

Operating an aircraft isn’t all about what goes on in the air. Stopping is just as important as going. Now, before we start considering this, a warning…. This is a fairly long piece! So go and make a coffee, get comfy, and we will be fine. Alternatively, read this in bed if you can’t sleep and be prepared for the shock when whichever device you are reading it on hits you in the face when you doze off!

Contrary to a fairly common belief, it is the wheel braking system which provides most of the retardation for aircraft. What about reverse thrust? Well, the thrust reversers on the engines are there mostly to help the wheel braking systems but are not the primary source of braking. Indeed, Airbus originally planned for the A380 to not have any engine reverse thrust. In the final version of the aircraft which went into service, reverse thrust is only available on the inboard engines.

So our main source of braking is wheel braking. But which wheels are fitted with brakes? Not the nosewheels, they are used exclusively for steering. And what may surprise some people is that not all the main wheels on the A380 are fitted with brakes. The most rearward wheels on the main undercarriage are just rolling wheels. You will see in the photo below that the wheels on the right are much cleaner due to lack of brake dust.

Big wheels!
Big wheels! (Captain @Colin__Dick and I inspecting the undercarriage)

Braking is normally carried out using an autobrake function. This also includes a rejected takeoff (RTO) function which applies maximum braking if the thrust levers are closed once above 72 knots during the takeoff roll. Many aircraft have an autobrake system. These are normally armed during the approach and landing briefing, which is typically carried out just prior to starting the descent. Most autobrake systems are set using either a numbered system, where higher numbers giving a greater braking force, or a descriptive system, such as that used on the A320 series, where either LOW or MEDIUM braking will be selected for landing.

Airbus introduced a revolutionary (sorry!) new system on the A380 called Brake To Vacate (BTV). It is optional on the A380, but fitted as standard on the A350. This advanced system allows the landing pilot to pre-select the runway exit they wish to take, and the aircraft will apply automatic braking as appropriate to allow this to happen in the minimum time. The system is quite complex, but works exceptionally well. We use this system for virtually every landing in British Airways as it allows us to pre-plan our exit from the runway, reduces brake wear, and is very comfortable for our passengers.

So how do we use BTV? Firstly we set up the aircraft systems for our expected landing runway. In this example, we will use runway 24R at LAX. Initially we need to look up the airfield and the specific runway on our LIDO airfield charts. You will remember from the previous blog that we have to make sure we only use those runway exits and taxiways which are colour-coded green, ie. suitable for the A380. Here is the runway exit chart for LAX runway 24R.

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So what is this showing us? Runway 24R is the runway at the top of the screen. You can actually only see the label for runway 06L here, but that is the same runway from the other end! Do you know how the numbering system works for runways? If you do, skip to the next paragraph. If not, it is actually quite simple. The two numbers are the first two numbers of the compass heading along which you will be pointing when looking down the runway. So in this case, 24 means the runway is set at about 240 degrees on a compass. Runway 18 would be pointing south, runway 09 pointing east etc. Runway 09 would also be runway 27 if you were using it in the opposite direction. If there is a letter after the numbers it means the airport has more than one runway pointing in the same direction so they are differentiated by R for right, L for left, and C for centre. I hope that is clear!

Just to the right of the 06L label on the chart you will see a green runway exit labelled AA. This is the usual exit we use at LAX when landing on 24R (The chart is orientated to the north, so when landing on runway 24R we will be moving from right to left down the runway as shown on this chart). The chart also clearly shows the green colour-coded taxiways the A380 is able to use. Anywhere not coloured green is out-of-bounds for the A380. So, for example, we could not use exit Z, the one to the right of AA. You will see on runway 24R itself there is some writing – 2721 G 46. This indicates the runway is 2721m long, has a grooved surface, and is 46m wide. 46m is a typical runway width. Some are 60m wide. Interesting to think the wingspan of the A380 is almost 80m and the distance between the outboard engines is 51.4m!

With runway 24R being 2721m long, a typical length, that should be more than sufficient for us to land on. But let’s make sure! For that we use the Landing Performance app installed on our Onboard Information Terminal (OIT). Below is the calculation performed for our flight. (Note that since I took the photos of the landing performance app and OANS displayed below, the runway length at LAX has increased by 1m! Thought I’d better get that in before the eagle-eyed among you did!)

Landing performance calculation
Landing performance calculation

Lots of numbers here! To summarise, on the left we enter the landing conditions and aircraft configuration. Top, centre, we select an available runway. We then press the ‘compute’ button, and after a few seconds the information in the ‘Results’ window appears. In this case the results show that for landing on runway 24R at 344.4 tonnes we should use FLAPS FULL, our landing distance LD will be 1656m. This is the minimum landing distance required using the autobrake setting we have selected, in this case, Lo braking. We use Lo braking as an indicator to start with as this is the most comfortable braking from a passenger point of view. This distance then has a 15% increment added to allow for handling and other variations on the day (the 1656m figure is that calculated as the best which would be achieved by the Airbus Test Pilots!), giving a Factored Landing Distance of 1984m.

The Stop Margin is how much of the runway will be left when the aircraft comes to a halt. GA Gradient is concerned with aircraft performance in the event of a go-around, so is not something we are considering at the moment. Finally, the figure towards the bottom right, VAPP, is the final approach speed, 132 knots in this case. Despite the A380 being such a massive aircraft, the landing speeds are comparable to A320s and the like.

We have determined we need 1984m of runway to stop the aircraft. We know from our LIDO chart that runway 24R is 2721m long, so that is fine. Now we need to determine which exits we are able to make. So lets display our OANS – the Onboard Airport Navigation System. This is effectively a ground-based satnav for the aircraft. It can either display our actual position on an airfield, or we can look up any airfield in the database for planning purposes.

Select the landing runway
Select the landing runway

In this diagram we have selected runway 24R, as indicated by the numbers being shown in blue. The OANS then displays the information it contains about the runway. Remember the 2721m runway length shown on the LIDO chart? OANS shows 2720m. This is one of our crosschecks. If the LIDO chart and OANS disagree by more than 35m, we are not allowed to use BTV. But here we are fine.

You will see two labelled magenta lines drawn on runway 24R. WET and DRY. You will not be surprised to hear that these lines show the position BTV braking has calculated it can stop the aircraft on a wet or dry runway. If possible, even on a dry runway, we would select a runway exit  beyond the wet line. Again, this is mainly due to passenger comfort, but also means the braking system isn’t working hard. Right in the centre of the above OANS display you will see a magenta up arrow with a magenta down arrow directly above it, and a small magenta dot in between. This is the trackball cursor. We would now move this over the top of exit AA, shown to the left of the screen, and beyond the wet line, and select this exit. This results in the display changing as shown below.

Exit AA now selected
Exit AA now selected

Exit AA is now shown in blue, and the display at  the top left shows EXIT AA 2145m, ROT 80″, TURNAROUND 100’/120′. So, exit AA is 2145m along the runway. This is more than the 1984m we calculated we would need earlier using Lo autobrake, so that is fine, and reconfirms the calculated lines BTV drew on the OANS. ROT stands for Runway Occupancy Time. In this case, BTV has calculated this to be 80 seconds for us to vacate the runway at exit AA. TURNAROUND is the time in minutes it will take for the brakes to have cooled below 150C, which we would need before performing another takeoff. There are two numbers. The lower one is the time if we use maximum reverse thrust on landing, the higher number is for reverse idle.

The last thing to do is arm the system using the autobrake knob.

Now all we have to do is land the aircraft in the right place at the right speed and BTV will control the deceleration for us. It is a superb system. It can be a little unnerving the first few times you use it! This is because it constantly monitors the aircraft speed and position on the runway and, unless you have asked BTV to enable you to vacate at a limiting exit, only applies a noticeable amount of braking fairly late on in the landing roll. This allows the aircraft to naturally decelerate after landing using air braking and reverse thrust, so minimising the work the brake system has to do.

Once it has initiated braking, BTV targets a constant (passenger friendly) deceleration rate to achieve a speed of 10 knots, 65 metres from the selected runway exit. However, if the exit chosen is within 300 metres of the runway end, this changes to a target of 10 knots at 300 metres from the end.

All sounds nice and rosy so far doesn’t it? So what happens if we land further down the runway than we planned and BTV calculates we cannot stop by the selected exit? Firstly, don’t land too far down the runway in an A380! (or any aircraft for that matter). Better to throw away a poor approach and do it again than try to make the best of a bad job. However, if the landing is only slightly beyond the normal landing point and a limiting exit has been chosen, or conditions on the ground dictate that the original exit now cannot be achieved because the deceleration rate is not what was expected, what happens next? Firstly, remember the best piece of advice ever given in The Hitchhiker’s Guide to the Galaxy. Don’t Panic!

On landing, the wet and dry lines displayed on the OANS are replaced by a single green STOP line. This shows where the braking system believes the aircraft will stop. It is constantly updated during the landing roll. If the green stop line goes past the BTV selected runway exit it turns amber, as does the label for the selected exit, a ‘triple click’ sound is heard, and EXIT MISSED is displayed. This is not too much of a problem in this case, as there is still sufficient runway to stop the aircraft, just not to vacate it at the point initially selected. However, what happens if the green line goes past the end of the runway?

This would activate the ROW/ROP – Runway Overrun Warning / Runway Overrun Protection systems. These are quite brilliant systems which are worthy of a blog all of their own. And if you have made it this far through this one, you are probably ready for a rest now! So we will cover those at a later date when we have gone through how to operate the A380 when everything is working well, to how we deal with situations where things aren’t going quite so sweetly….!

I hope the above has helped you understand how the superb BTV function works and enables us to bring the aircraft down to taxi speed in the most comfortable and efficient way possible. If there is anything which is not clear, or you have any other questions, please let me know via @DaveWallsworth on twitter and I will do my best!

If you enjoyed reading this and the previous blog, please pass on a link to anyone you think may be interested, and let me know what other aspects of flying the A380 interest you.

Best wishes, and happy flying.

Dave