Flying the Airbus A380 – Takeoff!
Thank you to everyone who has been so kind about my posts on Twitter. I’m glad (most of) you find it interesting. However, the limited number of characters available per post makes explaining the more complex aspects of flying the A380 a little tricky! So I thought I would start a blog where I can give more detailed descriptions about all things A380….
So let’s get the A380 into the air shall we?
Before we go blasting off down the runway we have to perform a takeoff performance calculation using our inbuilt application.
This screenshot shows the takeoff calculation performed for a takeoff from Johannesburg. So what do all the bits and pieces mean?
The first thing we do is select the airport, shown top centre of the screen in yellow. In this case FAOR / JNB. To the right of this selection we then choose the takeoff runway and which intersection we are expecting to use. Here, that is runway 03L and we are going to use the full length. The application displays the runway information immediately below. Quite a bit of detail here, but the main ones we are looking at are TORA – Take Off Run Available, here 4418m and whether there are any obstacles we need to be aware of, or let the application know about, in the area immediately after takeoff. There is also a small window below this information giving takeoff performance restrictions. This would detail items such as emergency turns we would have to perform should an engine fail during or shortly after takeoff. In this case, No Performance Restrictions Exist.
We then go through the process of loading information into the window on the left of the screen under Conditions. The first few are pretty obvious. We just type in the reported wind, temperature, pressure (QNH), runway conditions, and whether we are going to be using engine anti-ice. If you are not familiar with the flying definition of icing conditions, they may well come as a bit of a surprise. Here is the official definition we use:-
“Icing conditions exist when the outside air temperature on the ground or in flight is 10C or below and visible moisture in any form is present (such as clouds, fog with visibility of one nautical mile or less, rain, snow, sleet or ice crystals).”
There is also a further extension to this definition which covers the situation where there is no actual precipitation at the time, but the taxiways and/or runways have standing water, snow, ice or slush which could be ingested by the engines.
The reason a temperature of 10C can still cause engine icing is the cooling effect on the air as it is taken into the engine inlet. For the Rolls Royce Trent 970 engines fitted to BA’s A380s the engine anti ice system takes hot bleed air from the third stage of the High Pressure Compressor (simply put, centre of the engine) and uses it to heat the front part of the engine cowling (basically the silver bit you see at the front of the engine). More details on engines and compressors at a later date!
Back to the takeoff performance application. We next enter our expected takeoff weight. Here, 500.4 tonnes. Quite heavy! The next three items are the configuration, ie flap setting. We usually leave this in Opt Conf – optimum configuration, unless there is a good reason not to. Air Cond specifies whether we will be using some bleed air from the engines to power the air conditioning and pressurisation systems during the takeoff. This is similar to the anti-ice detailed above. Using some of the bleed air from the engines to power the air conditioning does slightly reduce the power available for takeoff. In some cases we can use either the APU (small jet engine in the tail) to power the air conditioning, or even perform the takeoff with the air conditioning systems turned off, to achieve maximum thrust. We currently use the APU to power the air conditioning during takeoffs from Hong Kong and Singapore as these present the highest takeoff weights for us on the British Airways network. For all other takeoffs we use engine bleed air.
Finally, most takeoffs are performed using Flex Thrust. Describing Flex Thrust could be a blog itself! So here is the shortened version. If we were taking off at the maximum weight the performance of the aircraft would allow on the day we would have to use maximum thrust. However, we usually take off at a weight below this maximum. It therefore makes sense to reduce the wear and tear on the engine by reducing the power below maximum. You don’t always drive your car with the accelerator on the floor do you? (Unless your name is Jenson Button!)
In simple terms, the maximum available takeoff thrust varies with outside air temperature (OAT). As the OAT increases, the air density decreases, so reducing the amount of power the engine produces. So let’s look at our particular case. We can see from the data we entered into the application above that the actual OAT for our takeoff is 16C. However, look at the number next to the green FLEX almost in the middle of the screen, in the Results window. It is showing 35C. So the application has determined that we can use an ‘assumed’ temperature of 35C for the engines for this takeoff rather than the actual temperature of 16C. By telling the engines to use this flexible temperature of 35C instead of 16C, they will not go to maximum power, and so reduce the wear and tear.
The A380 can operate over such a range of weights that the reduction in engine power required for takeoff can be quite large. The limit states that the takeoff thrust cannot be reduced by more than 40% of full rated thrust. This is a much greater reduction than allowed on most aircraft. But going back to Jenson and his car, although he will probably spend quite a proportion of his time when racing with his foot hard down on the accelerator, you would expect him to be far more lenient with his own car when driving on normal roads! This is exactly the situation when we are flying. We can use full power when needed, but it is far better for the engines if we back off a little from this when we can.
Don’t worry! We are almost there! In addition to calculating how much power we need to use for takeoff, the results window shows us our takeoff speeds and flap setting. V1 is the speed beyond which we are going to takeoff even in the event of an engine failure. VR is the speed at which we will rotate, ie pull back on the sidestick to lift the nose up. V2 is the takeoff safety speed. This is the minimum speed we must fly after takeoff. There are three possible flap positions for takeoff on the A380. Here, we are going to use the first one, Flap 1+F, which is the least amount of flap we would ever use. Other flap settings available to us are Flap 2 and Flap 3. These would normally result in lower takeoff speeds, but would have consequences for the rate of climb achieved immediately after takeoff. There is a balancing act to perform here, and the takoff performance application is usually left to decide the best setting. I will cover the specifics of flap settings and what they mean in a later blog….
Now we have all the information we need. We know how much power to use, which flap setting to use, and how fast we need to be going before we can fly. So let’s get on with it!
We line up on the runway and make sure everything is good for takeoff before moving all four thrust levers forward together to approximately 30% thrust. The A380 uses a thrust system called ACUTE to show how much power the engine is producing as a percentage of the maximum power available. (ACUTE = Airbus Cockpit Universal Thrust Emulator)
This is shown by the top dials on the screenshot above. In this case the engines are actually running at around 73% thrust as the photo was taken in the cruise. It is a little busy at takeoff to be taking photos of the instruments!
Once the engines have all stabilised at 30% we advance the thrust levers further into the FLX position. This tells the engines to produce the amount of power we previously calculated. The engines accelerate rapidly from 30% to the required, calculated thrust and off we go! If you have flown with us on our A380s you will, no doubt, be aware of this two stage engine acceleration. There are also a couple of other functions which prevent the engine from operating at certain rotation speeds during the takeoff roll which can result in there being more than one acceleration from 30% to takeoff power. The one which we see most is called METOTS (Modified Engine Take-Off Thrust Setting). It prevents the engine from exceeding 78% N1 below 35kts. This is an engine protection system to prevent fan instability. N1 is the actual rotation speed of the big fan you see at the front of the engine, expressed as a percentage. It is shown just below the ACUTE THR dials. We will often see the engine increase to a power just below the METOTS setting, then as the airspeed increases, a final extra push in the back comes as takeoff power is reached.
The other information on the screenshot above is the EGT (Exhaust Gas Temperature). This is the temperature of the air passing over temperature probes at the rear of the engine.
So now we are accelerating down the runway. The handling pilot (HP) will be spending most of their time looking out of the window, making sure the aircraft is tracking down the runway centreline using the rudder pedals to make very small changes to direction. The other pilot, or non-handling pilot (NHP), will be monitoring all the aircraft parameters very closely, especially the engine and flight instruments and looking for anything out of the ordinary.
This screenshot shows the other engine information. N2 and N3 are internal spinning components of the engine, FF is the fuel flow in kg per hour. The oil quantity is measured in quarts. The PSI is the oil pressure, then there are three vibration indicators for the three spinning sections, and finally an engine nacelle temperature dial. In many ways the NHP is the harder working of the two pilots at this stage as they are monitoring all these parameters while also making sure the HP is tracking the centreline properly, in addition looking at the flight instruments to make sure all the airspeed indications are accelerating correctly and all giving the same speed. The HP is just grinning from ear to ear as they control 500 tonnes of A380 as it accelerates rapidly down the runway!
At 100 knots airspeed, the NHP announces “one hundred knots”. The HP looks down and checks their airspeed indicator, makes sure it also reads 100 knots, and states “Checked”. We use 100 knots as a speed below which we would be ‘stop minded’ if we have a problem, and above which is it probably better to continue the takeoff and deal with a problem in the air due to the problems associated with stopping from high speed. So, from this point on, unless we have a major problem, we are not going to stop. Once we reach V1 an automated voice will announce “V1”. From this point on, no matter what problems arise, we are going flying as there is insufficient runway left to stop. In our case we still have 16 knots left to accelerate before the NHP announces “Rotate” at Vr. Now the HP gently pulls straight back on the sidestick, watching for the horizon to drop out of view at a constant rate, and briefly glancing at the flight instruments to ensure all is well. We want to rotate the aircraft at around 3 degrees per second, initially aiming at a climb-out attitude of around 12.5 degrees. The initial rotation takes a little time to establish, but once the nose has started to lift the pitch rate remains fairly constant for a given sidestick input.
We are now flying! (The grin just got even wider!). The NHP announces “Positive Climb” to which the HP announces “Gear Up”. The NHP moves the gear lever then all 20 mains wheels and 2 nosewheels are lifted up, landing gear doors close, and there is a little ‘squeak’ from the nosegear area as everything stops moving, which never fails to make me smile! It is almost as though it is saying, very quickly and excitedly, “Up!”
Once all the wheels are packaged away there is a very noticeable drop in noise level. It is amazingly quiet in the cockpit.
We continue flying away from the ground until, normally, at around 1000 feet above the airfield the HP will lower the nose, reduce the thrust to climb thrust, and start to accelerate to S speed. This is the speed, shown on the airspeed indicator, at which the flaps can be retracted completely. The HP will ask for this to be done by stating “Flaps Zero” (sometimes followed by “Please” by those who have been brought up correctly!). The NHP repeats “Flaps Zero”, checks the speed is correct, and moves the flap lever. Now we can accelerate to the usual climb speed of 250 knots when below 10000 feet, and once above that, a typical climb speed of around 330 knots.
Then it is time for something very important. A nice cup of white tea, no sugar please!!!
So how much fuel do you think the massive Rolls Royce engines on our A380 use on takeoff?
Well, on the last takeoff I flew the flow rate of fuel into each engine on the runway was 8200 kg per hour! So the total flow rate of fuel used on that takeoff was 32800 kg per hour! Considering how much power is being produced, and how heavy the aircraft is at takeoff, it is quite remarkable how quiet it is both inside and outside.