This project is a spin-off from the Airbus MCDU Emulator Project. It is based on the same technology, but with more advanced techniques and features. These upgrades are planned to be implemented into the next version of the MCDU emulator.
This A10 project is significantly less complete, and most importantly it does not yet contain any lesson content.
To get started, click the "AAP" tab under the CDU and set the switches for CDU and EGI to "ON". Then click the CDU tab at the bottom to go back to the CDU view.
CDU start up screen should be displayed. You can click on the SYS, NAV, or WP buttons to see more options.
If you set the PAGE switch on the AAP panel to POSITION, the CDU will show position info instead of the normal pages of information. Switch it back to OTHER for normal operation.
Proper lessons are coming soon. If you would like to buy a hardware version of the A10 CDU which will be compatible with X-Plane, DCS, or Prepar3D, please contact mcdu at equicom dot net and be sure to put A10 hardware in the subject line.
IMPORTANT: You should use this site with Chrome or Chromium browser for best results because other browsers may have too many keyboard quirks that will quickly become annoying (for example, the QuickFind feature in Firefox, or the way Firefox uses the backspace key for navigation).
For most users, it will be best to switch the browser to full screen mode (F11), so that the screen won't scroll unintentionally.
REALLY IMPORTANT: This page requires a minimum viewport area of 900px wide by 600px high. It is NOT intended to be used on a smartphone or mobile phone display, but will work on tablets that meet the minimums. You will get best results with a PC running Chromium for Linux in full screen mode.
UPDATE: From August 2017 we fixed this problem slightly. It will now scale the entire screen on Android phones. Unfortunately if your phone has a very small screen, that may make it difficult to read the text.
In the lesson panel on the left side of the page, you will see it has been divided into 3 sections.
The top section shows the available lessons, displayed as a row of buttons. Each lesson is designed to follow from the previous one, so it is best to complete them in order from left to right.
The middle section is the lesson body, which contains all the content of the lesson.
If you see a green button, this means it leads to information that is essential for continuing (exception is on the preflight checks page, where color has no meaning). Blue buttons link to information that may be of interest, but is not essential.
The lesson body may need to be scrolled in order to see all of the content. It is important to remember that when moving between pages, on most browsers the scroll position will not be reset (if you know how to do that without refreshing the page, be sure to let us know). You will need to scroll back to the top yourself.
The bottom section divides the lesson body into pages, making it easy to go back and review what you have already read before.
Most of the time, you should read every page of every lesson. The exception is lesson 1: Check & Start. For that lesson, you can skip straight to page 5 if you have no interest in real-world aviation and only want to learn the MCDU procedures.
This help file is due to be updated and will be given a new separate page with much more detail.
For now, we felt it is better to just get the most vital information out there as quickly as possible, so you can started. We will make fixes as we go, and continue adding content as it becomes possible.
Our site is famous for two reasons... first and best, because of our attention to detail and our solid attempt to create the most realistic free online training tool available for the MCDU. But unfortunately we're also famous for how slowly we can make updates.
We'd like to improve on both counts! And that's where you have the opportunity to help.
This product is available to the public totally free of charge and we don't make any profit from it at all. We volunteer our spare time to work on the project and unfortunately there is less and less of this spare time available.
So we are now asking any enthusiastic volunteers who would like to see this project reach its full potential to assist with developing the project. It is really easy to help and you don't need to be a programmer to do it!
You can help us by adding new airports, waypoints, routes etc. If you can spare just one hour to help with that, even if you only add one line of data, it will go a long way towards getting this project up in the air :)
Everyone who helps will get a shiny new developer credit that you can display on your CV or brag about to your friends or whatever else you want to do with it.
Please use the email contact form to get in touch if you are interested. Also any active duty or trainee A320/A330 pilots (or similar) who would like to help in other ways than adding data, we are also very keen to talk with you!
My sincere thanks to everyone who has helped us to keep this project alive for another year, and I truly hope we can continue to make things even better.
xmodmap -e "pointer = 1 25 3 4 5 6 7 8 9"
When we first started this project, many airlines were still using the older MCDU hardware with just software updates, so many of them had a simple OFF/BRT knob that you rotated to adjust the brightness or turn the unit off. That is no longer the case and it is much more common to encounter the newer hardware, so we have implemented a long overdue update to the interface. Now you use the BRT and DIM keys to switch on and off. We have not added incremental brightness yet, but it is planned for the near future.
New
FANS
/ ATC COMM tutorial available!
Additional information is available from
document
or visit
IBAC website).
For now, it works in a much simplified manner. Tough break, but we need more money!
Fixed PERF CLB / CRZ / DES pages.
Built framework for PERF APPR page, but it does
not display yet (needs a little coding, thanks for
your patience and understanding).
Now also working on some new LATREV functionality.
Added section to website to allow you to
participate in developing this project.
For the moment, because I don't yet have any other place to bring this notice to attention, regarding the soon-to-be-implemented communications features, I would like to present this document containing potentially important information regarding the nature of communications messages and some of the matters that you should be aware of. Eventually we will get around to providing a tutorial on all this stuff here on the MCDU website. The features will be available before the tutorial is ready, so that is why I have made the link to the document, which is not a tutorial but does raise some important issues that will undoubtedly be of help to you in your training.
| Item | Check | Check |
|---|---|---|
| lights | condition | working |
| AOA probe | condition | |
| static ports | condtion | clear |
| ASI valve | condition | |
| avionics door (L) | closed |
| Item | Check | Check |
|---|---|---|
| pitot probes | condition | |
| TAT probes | condition | |
| crew O2 discharge indicator | green | |
| radome & latches | condition | closed |
| static ports | condtion | clear |
| avionics door (F) | closed | |
| ice detection probes | condition | |
| ground elec pwr door | closed |
| Item | Check | Check |
|---|---|---|
| taxi light | condition | |
| chocks | in place | |
| wheels & tires | condition | |
| superstructure | condition | |
| hydraulics & electrical | condition | |
| wheel well | check | clear |
| shock absorber | condition | |
| safety pin | removed |
| Item | Check | Check |
|---|---|---|
| AOA probes | condition | |
| TAT probes | condition | |
| pitot probes | condition | |
| static ports | condtion | clear |
| cargo loading operation access door | closed | |
| cargo operation access door | closed | |
| cargo door | closed | |
| lights | condition | working |
| avionics doors (R1 & R2) | closed | |
| avionic vent outlet valve | condition |
| Item | Check | Check |
|---|---|---|
| LP ground connection door | closed | |
| antennas | condition | |
| drain mast | condition | |
| anti-collision light | check | |
| pack air intakes & outlets | clear | |
| HP ground connection door | closed | |
| ground hydraulic connection (blue) | closed | |
| L/G ground access door (L) | closed | |
| L/G ground access door (R) | closed | |
| ground hydraulic connection (yellow) | closed |
| Item | Check | Check |
|---|---|---|
| inner-tank magnetic fuel levels | flush | |
| fuel water drain valves (inner tank) | no leaks | |
| refuel panel | closed | |
| landing light | condition | working |
| slats | condition |
| Item | Check | Check |
|---|---|---|
| engine oil fill access door | closed | |
| master magnetic chip detector access door | closed | |
| thrust reversers cowl door | closed | |
| pressure relief doors | closed | |
| fan cowl door | closed | |
| drain masts | condition | no leaks |
| access door to reversers latches | closed | |
| engine inlet and fan blades | check |
| Item | Check | Check |
|---|---|---|
| thrust reversers cowl door | closed | |
| pressure relief door | closed | |
| fan cowl door | closed | |
| access to starter valve manual override | closed | |
| turbine exhaust | clear |
| Item | Check | Check |
|---|---|---|
| refuel coupling door | closed | |
| magnetic fuel levels | flush | |
| fuel water drain valves (outer tank) | no leaks | |
| slats | condition |
| Item | Check | Check |
|---|---|---|
| fuel ventilation overpressure disc | intact | |
| wing fence | condition | |
| magnetic fuel levels | flush | |
| fuel water drain valves (surge tank) | no leaks | |
| surge tank air inlet | clear | |
| slats | condition | |
| nav lights | condition | working |
| antennas (top) | condition |
| Item | Check | Check |
|---|---|---|
| control surfaces | condition | |
| flaps & fairings | condition | |
| static dischargers | check | |
| static discharge eliminators | check |
| Item | Check | Check |
|---|---|---|
| chocks | removed | |
| wheels & tires | condition | |
| brakes & brake wear indicators | condition | |
| superstructure | condition | |
| hydraulics & electrical | condtion | |
| downlock springs | check | |
| safety pin | removed |
| Item | Check | Check |
|---|---|---|
| refuel electric control panel | closed | |
| APU fuel drain | condition | no leaks |
| ground hydraulic connection (green) | closed | |
| antennas | condition | |
| drain mast | condtion | |
| cargo loading operation access door | closed | |
| cargo operation access door | closed | |
| cargo door | closed | |
| bulk door | closed | |
| waste service panel | closed | |
| outflow valve | condition |
| Item | Check | Check |
|---|---|---|
| stabilizer, elevator, fin & rudder | condition | |
| static dischargers | check | |
| lower surface | check | |
| flight records access door | closed | |
| The main thing to be looking for here is any evidence of a previous tail-strike. | ||
| Item | Check | Check |
|---|---|---|
| access door | closed | |
| air intake | condition | |
| exhaust | clear | |
| nav light | condition | working |
| fire ext overpressure disc | in place |
| Item | Check | Check |
|---|---|---|
| stabilizer, elevator, fin & rudder | condition | |
| water service panel | closed |
Sometimes this is just a temporary problem, for example loss of connetion with SATNAV, but if it is a real fault, the GPS may have frozen. You may be able to correct it by rebooting the FMGC.
Note: We didn't think you'd want to wait for the system to boot realistically, so in the emulator you can skip waiting by pressing LSK1 again.
Currently available routes in this version:
Planned for future version:
Planned for desktop version:
Note: This feature can't be included in the online version due to the amount of data that has to be loaded. Even this version you are viewing now, which is incomplete, contains more than 10,000 lines of code. The full version could be a million lines.
If you only enter FROM/TO data directly, then you are only telling the MDCU where you want to go, but not how you want to get there.
That means a lot more work for you, because you will have to manually enter every waypoint, psuedo waypoint, and other information. So boring!
Stored company routes (Co-Rtes), on the other hand, have most of that data already preset, so all you need to do is check it and make minor modifcations.
Normally you would only use FROM/TO if you are flying some place your airline doesn't normally go. In every other case, you definitely want to be using Co-Rtes. They save you so much time and effort!
The term "Flight Level" is used to divide airspace above 9,999ft into vertical sections of 100ft.
For MCDU purposes, any altitude above 9,999ft is referred to by its flight level (eg FL100 for 10,000 feet). So when you are looking at the flight plan, it will always use FL for higher altitudes.
Be aware that, depending on what country you are flying in, local ATC may not necessarily adhere to the proper use of the term "Flight Level" (but they should always understand it).
Thus in some parts of Europe it is not unsual to hear references to Flight Levels below 100 (the correct minimum altitude for FL), while in the US it is rare to hear FL used for altitudes below FL180.
The important thing to remember is that the MCDU normally reports all altitudes over 9,999ft as FL, although there are some exceptions (for example, the Tropo value on INIT A).
The "Cruise" phase of your flight (abbreviated to CRZ in MCDU terms), is supposed to be the portion of it where you are obtaining maximum travel at maximum economy. Usually this means flying at higher altitudes where you can get a high rate of knots with less engine power (fuel flow).
In general, for every 1000ft increase in altitude below tropopause, you can expect the outside air temperature (OAT) to drop by about 2°C (actually if you want to be really precise, it's closer to 1.98°).
Rounding the value up to 2 just makes calculations more simple, because now you can work out that it is approximately a difference of 10° for every 5000ft.
That formula is not 100% accurate because there are a few different factors such as humidity, wind, and even the curve of the Earth, that affect the result.
It is important to understand that this effect of temperature decreasing with altitude is only true until you reach tropopause. After that point, the air begins to get warm again.
By now, if you've been reading through all the information, you will know that tropopause is a tipping point where air temperature stops getting colder with increased altitude and actually starts getting warmer.
It's more accurate to describe it as the border between two different atmospheric regions: the troposphere and the stratosphere.
I don't want to get overly technical here, so the thing to understand (and help you remember) about the difference between these two atmospheric regions is that the troposphere is low and moist, and the stratosphere is high and dry.
Still in over-simplification mode, the quickest answer for why that moist air is colder than the dry air above it, is that adding unheated water to something tends to have a cooling effect.
Too simple? Well if you're really interested, keep reading. But this knowledge isn't really essential for what you came here to learn.
As you already would know, air is a mixture of different gases such as nitrogen, oxygen, and hydrogen. There are many other gases mixed in there too, as well as isotopes of these gases.
At the lower atmospheric level (the troposphere), there is also a lot of water vapor cluttering up the air. That water is being pulled up from ground level due to evaporation.
As water molecules are on their upward journey, they don't travel in straight lines. They are affected by all kinds of forces. This causes them to bump into each other a lot. And when they do that, there is a potential for them to form hydrogen bonds with each other.
When enough of these molecules have bonded, they become heavier than the gas molecules around them (a lone water molecule is a fraction lighter than a lone oxygen molecule, but when the water molecule is fully bonded with 4 others, it will weigh 3.125 times as much as the oxygen molecule).
Because the bonded water molecules are heavier, it means they are being pulled towards the Earth at a faster rate by gravity than the gas molecules are.
So they tend to reach a maximum altitude of between FL360 and FL380. And of course they are still flying around and banging into each other.
As they do that, due to their high surface tension they have a tendency to cling together, condensing, and thus become even heavier, until they eventually find their way back to ground level again in the form of rain or snow.
And that is why water molecules don't typically make it into the stratosphere.
A few claim to have done it, but their stories haven't been verified yet.
You need to refer to the national weather service for the country you will be flying in. Our tutorial bases you in the US, so that is the example I will provide.
When you click on the green button below (not the blue one!), the site will open in a new tab or window. You will see a map dividing the country into 9 regions.
You would select the region you were interested in getting information for, and then scroll down the list of fixes until you find the IATA code for the place you want to know about.
The chart will actually show full "winds aloft" information, and it's all in code. It is divided into rows and columns with the left side column showing the IATA codes, the top row showing altitude in feet, and the remaining columns have coded data.
Those complex-looking codes are actually quite easy to decipher if you understand them. The first 4 digits tell you the wind direction (crs × 10) and speed (kts × 1), and the last two digits are the air temperature (normally temp°C × −1).
So for example the code 123456 would mean wind from 120 degrees at 34 knots, and OAT of −56°C.
A code of 090909 would mean wind from 9 degrees at 9 knots, and OAT of −9°C. Very simple when you know how to read it!
PAT just means "Pressure, Altitude, and Temperature". These are the main factors that affect how well your engines work.
We have already covered temperature, so that just leaves pressure and altitude, and these are so closely related that it's not worth dealing with them separately.
There's a lot of technical stuff we could get into on this subject but the important thing to know is that as you climb, the air gets thinner and has lower pressure.
Now you probably already know that high density air creates more lift than low density air, so how can climbing to high altitudes be an advantage?
The explanation is probably not what you're expecting.
This is going to sound strange, but it's because there is less air in the air. In other words, because the air is thin.
That is a factor because air and fuel have to mix in the engines at a very precise ratio to produce optimal combustion.
Now because there are fewer air particles actually getting into the engine, then to get the same optimal combustion you have to maintain the ratio of fuel to air, which means that you have to decrease the amount of fuel in the engine so that the amount of fuel is not too high compared with the amount of air.
So now you're actually using less fuel and still getting optimal engine performance.
GL123: Laker one-twenty-three heavy, Minneapolis Clearance, request departure runway 4, reason high loadout [reason is optional, but polite]
CD: Minneapolis Clearance, Laker 123, request received, please stand-by for instructions.
GL123: Laker 123, Clearance, roger, awaiting your instuctions.
... delay ...
CD: Minneapolis Clearance, Laker 123, approved departure 4, ETD on time as filed, call when ready for pushback.
GL123: Laker 123, Clearance, roger we take runway 4. Thank you.
[Notice that this example is modelled on real world chatter, which is much less formal and more polite than what you will hear on simulator networks such as VATSIM which actually enforce stricter rules than would apply in the real world. Therefore it may seem a little odd, especially since the callbacks don't strictly conform to correct procedure, where you are supposed to repeat every instruction word-for-word — people just don't actually do it].
The first thing we need to factor is the "empty weight" of the aircraft (in the case of the A320-211 this is 42,300kg). Each passenger is assumed to be just 70kg and carrying 5kg of cabin baggage (total = 75kg/pax).
Note: That is something that will need to be reviewed in the near future for safety reasons. It's obviously absurd to think we can average out the weight per pax to just 75kg, because it does not take into account the increasing rate of obesity, or that many pax try to cheat the cabin bag allowance. From a safety point-of-view, it would be much better to assume average weight per pax at about 100kg, but so far nobody seems to want to face up to that inconvenient truth.
For tutorial purposes, we will stick with the "official" weight per pax figure (75kg), and assume there is a full load of 150 pax (the aircraft in the tutorial is an 320-211) plus 8 crew, this gives us a subtotal figure of 158 × 75 = 11,850.
Now we need to add that to the 42,300kg of empty weight, giving a new subtotal of 54,150.
Our ZFW limit is 60,500kg so we need to hope that cargo does not exceed 6,350kg. For now, let's assume that we have about 3,500kg of cargo. This means our total ZFW is now 57,650kg. We must round this total up to 57,700 and this is our final ZFW total.
That was the easy part!
Now we need to explore the even more complex problem of Center of Gravity, or "CG".
First thing to understand is that the CG is expressed as a percentage of the aircraft body relative to the center. "Forward CG" is CG where the balance is closer to the nose of the aircraft, and "Aft CG" is NOT the opposite of Forward CG!!!
CG greater than 50% would be abnormal and have a severe effect on performance. This would result from something dramatic happening, such as something breaking loose during the flight, or all the passengers running towards the tail of the aircraft and stopping there.
So true Aft CG is not something you'd normally have to think about. For most pilots, the term Aft CG refers to CG values greater than 25%, and Forward CG refers to CG values below 25%. Obviously the default CG of 25% is simply a point of reference and not necessarily the ideal CG, as some people erroneously think.
The concept of ideal CG is way too complex to give it a fixed value. The ideal CG will vary for each flight depending on the conditions for that flight. It also depends on who is making the decision about what is ideal. For the airline, it is about what gives the most efficiency. Other people with different values will not necessarily agree. But the CG is not decided by the pilots, it is merely reported by them to the MCDU.
Other people do their best to distribute the load according to airline policy of "load profile", which is effectively a managerial decision rather than operational. Operational factors should always take priority over managerial policy (and if they don't then you work for a bad airline!), so everyone on the operational side of things will be making decisions constantly right up until the moment the doors are closed. That also includes cabin crew redistributing passengers if necessary.
Pilots will be given information about how the load is distributed relative to the CG and they can then make decisions taking this value into account. CG isn't even a fixed value. We actually should think of it as a "CG Envelope", because things happen in flight that can momentarily shift the CG slightly.
Your job will be to examine all the data you are provided with and then give an appropriate CG value to the MCDU so that the correct information is fed to the FMGC and all of the calculations are based on actual operating conditions and not just the default value.
Certainly for use in home simulator games such as Microsoft Flight Siumlator, Flight Gear, or X-Plane, you don't have to worry about the CG factor in a realistic way, but in any real world aviation your figures need to be based on actual conditions and not just estimates in this case.
We will cover the topic of the effect of CG on performance in more detail in the book, as it just requires too much detail for the online learning environment.
The fields for the INIT B / INIT FUEL PREDICTION page tend to cause the most confusion (notwithstanding that this page changes its name after you complete the data for it).
Hopefully this quick guide will help to clarify what all those strange looking fields are for.
TAXI: This is the amount of fuel used for moving the airplane on the ground.
TRIP/TIME: This is the calculated total fuel burn for the trip and duration of trip.
RTE RSV/%: This is a percentage of fuel used for "special purposes", normally fixed at 5%.
ALTN/TIME: Only active if there is an ALTN RTE set up.
FINAL/TIME: This is an estimate of the amount of fuel used while holding for final approach.
EXTRA/TIME: Actual fuel reserves for emergency use, in case you have to divert, etc.
TOW: Calculated take off weight (ZFW+Block). Must not exceed MOTW.
LW: Estimated weight on landing (ZFW+EFOB@Dest). Must not exceed MLW.
Remember when you were learning math in school and you thought it was probably all just going to be a waste of time and effort? You were probably right. But that's beside the point.
Calculating the block value is not really difficult provided that you understand a few basic rules.
The first thing to be aware of is that the estimate is not based on what you expect to burn, but the maximum burn if you ran your engines at full power for the entire duration of the flight.
This, you will probably realize, means you will always have more fuel than you are likely to use. That's not such a bad thing when you think about it.
If you look at your F-PLN page, you will see that the distance of this flight is 1426NM (about 2640km) and the expected duration is 3 hours 30 minutes. Maximum fuel burn with these engines is approximately 3000kg/hr, so this means your starting point for the calculation is 3000 × 3.5 = 10,500kg.
FAA regulations (Tile 14, Part 121.645(c)) require that for a flight such as the one in our demo flight (KMSP/KSFO), where no alternate airport is listed, that we must carry at least enough fuel for 2 more hours of continuous flight at maximum burn (so at least another 6000kg).
Total is now 16,500kg. You need to add 200kg for taxi time, so now you have 16,700kg. Finally, you are supposed to allow an extra 5% for special purposes, so you can add another 835kg for a total of 17,535kg.
So after all that, you end up with 17.5 as the block value.
"V speeds" are pre-defined terms of reference for speeds at which certain events or actions can be expected to occur, depending on the operational conditions in effect when that speed is reached.
For example, the action associated with V1 only occurs if there is an operational necessity for that action to occur.
There are a lot of V speeds on the list — nearly 70 in fact — but for now we will just discuss the 3 main ones associated with the V1, V2, and VR fields on the MCDU PERF page.
V1 — this is the theoretical "point of no return". Beyond this speed limit, the pilot is supposed to be committed to take off no matter what. So if all four engines on a 747 are not working, you are actually expected to take off at that speed (and I am sure you can see how impractical that is).
VR — sometimes written as VROT, is the "rotation" speed, which really means the point at which the PF would use physical input to attempt to cause the aircraft to lift off.
Note: Some aircraft such as the F-16 in clean configuration don't have a practical VR because they will become airborne without pilot input once they reach V2 and in fact they will almost fly themselves on takeoff. Unfortunately the Airbus is not quite as cool as a fighter jet.
V2 — this is the speed at which the nose should leave the ground. In many cases it may be the same as VR, but sometimes V2 is a little faster because in some conditions it may take more time for the plane to respond to the input.
This is really a two part field, but in many cases the value of both parts is going to be the same. The exception is when noise abatement takeoff is required, in which case you may use different values.
THR RED = Thrust Reduction Altitude. It is the point where the pilot can move the thrust lever from the TOGA or FLX/MCT positions to the CL position.
THR ACC = Thrust Acceleration Altitude. Always at least equal to THR RED. This is a phase transition point between Takeoff and Climb.
When possible, it is recommended to use Flaps 2, because this will normally give you the best performance. If you use setting 1+F then the takeoff may be slightly less efficient, but this does have the advantage of providing automatic flap retraction.
You should not use Flaps 1 for takeoff. If you want position 1, then you should use 1+F. Flaps 1 is rated 15kt higher than 1+F, and a full 30kt higher than Flaps 2.
Of course the actual setting will depend on the operating conditions.
The 1+F setting gives you a reduced margin for error on VR, so if you get something freaky happening, such as a wind shear, at the exact moment you reach VR, it is likely to have greater effect when on Flaps 1+F than on Flaps 2.
At last — the secret to instant weight-loss, revealed right here for you on this very page!
After calculating block value, you may find you are still not happy with the TOW and LW factors, even if the MCDU accepts them and they are within regulations. But don't worry — you can solve this problem easily.
You already know that the minimum fuel you can have on board at the final waypoint is 6.0T, so all you need to do is hit the AIRPORT key and look at the EFOB number in the bottom-right corner.
Subtract 6 from that number, and this will give you the amount you can (somewhat) safely adjust your block value by. Then just go back to INIT-B and enter the new value.
Even though FANS is not a very complicated system, it has been suggested that it has not been documented well. The documentation is very technical and can be confusing, plus it does not discuss every possible scenario, nor does it provide many screen shots of the MCDU (and only a few screenshots of the DCDU).
ATC operators and pilots may use accented speech when communicating by voice, and sometimes verbal instructions can be misunderstood (for example "Descend for four thousand feet" or "Descend four four thousand feet"? "Descend to two thousand feet" or "Descend two two thousand feet"? Mixing these instructions up can be fatal! And it has happened!).
Just to really briefly summarize the differences between how FANS A and FANS B work, FANS A uses ACARS for all communications between the aircraft and either AOC or ATC. For communication with AOC, FANS A uses all available I/O sources (VDL-A, VDL-2/AOA, SATCOM, HFDL) but only VDL-A and SATCOM to communicate with ATC, except in the case of the FANS A+ variant, which can also use VDL-2/AOA and HDFL as a supplement for ATC messages.
FANS B uses ACARS and all available I/O sources for communication with AOC just the same as FANS A does. But when communicating with ATC, FANS B does not use ACARS. Instead it uses the Aeronautical Telecommunications Network (ATN), and only VDL-2.
The most crucial thing to understand about the differences is that with FANS A, the data link is intended to be the primary communication method with voice communication as a backup. In a FANS B environment, voice communication is the primary method to be used for communicating with ATC and the data link is supposed to supplement this. FANS B aircraft can still use the data link as the primary communication method with AOC, however.
FANS A+ installed on an A320 or A380 will work in a FANS B environment over the ATN but you will only have access to a limited range of functions compared to if you had FANS B installed. If you are flying the A330 or A340 then you are not able to connect to ATN.
Conversely, if you have FANS B installed, you can't connect to ATC in an ACARS only environment.
In all Airbus aircraft except the A380, you receive messages via the Data link Control and Display Unit (DCDU), which is a tiny device that sits above each of the MCDUs on either side of the lower ECAM display. You compose messages using the MCDU. The DCDU in these aircraft is controlled by the use of physical pushbuttons.
In the A380 it is quite different. Here you have a single DCDU display located between the lower ECAM display and the thrust levers, while on either side of the lower ECAM display there is an "ATC Mailbox" display. Both the DCDU and the ATC Mailbox display screens are controlled by touch screens.
In theory you can use the MCDU to set up a message in the A380, but in practice you probably wouldn't, since the large ATC Mailbox display with its touchscreen interface is supposed to make your job easier.
The DIR TO request is simple to understand. You are requesting permission to change course so that you will be enroute to a specific destination, waypoint, fix, or other recognized navigation point.
To initiate this request, type the code of the required destination and then press LSK1. For example, on leaving KMSP via the LEINY2 departure, the next waypoint after reaching the top-of-climb is MBW. If you wanted to skip this waypoint for some reason and proceed to MTU directly, you'd type MTU and press LSK1.
The final step in making the request, assuming that you don't wish to qualify it, is to press LSK6R.
WX DEV is a deviation due to weather. You are requesting a deviation of a certain number of miles left or right of your current ground track to temporarily deviate around the bad weather.
The request is formed in 2 parts. The first is a numeric value indicating the number of miles, and the second is a letter value (either L or R) indicating the direction of the deviation (left or right).
So for example a value of 5L means "5 nautical miles left of track" and a value of 11R means "11 nautical miles right of track."
You lock in your entry with LSK 1R and send it by pressing LSK6R. There is no need to qualify a WX DEV request because the reason is implied in the title.
Use this when you want to select a different STAR from the one filed on your plan.
To initiate the request, type the identification of the STAR and press LSK2, qualify if necessary (LSK 5R) and then send (LSK 6R).
Don't forget to update STAR in FPLN.
An offset is similar to a deviation. In this case you also are specifying where the offset should start from, so for example "5L/LEINY" will generate a DCDU message similar to:
AT LEINY REQUEST OFFSET 5 NM LEFT OF ROUTE
And the ATC response generated would be (if granted):
AT LEINY OFFSET 5 NM LEFT OF ROUTE
Note that this message could also be sent to you as an instruction, not always as a result of your own request.
After typing in your request (always in the format shown, eg: 7R/OAL) you would press LSK 2R to lock it in, and then LSK 6R to send the message to the DCDU ready for review and sending.
Important: You can specify a time instead of a waypoint for the AT clause. For example, you could type 5L/2250 and the 2250 will be interpreted as a time instead of a place. Useful when you're a long way from any waypoint.
This one is really easy because it is specifying an exact heading. You just type a number between 0 and 360 and press LSK3 to lock it in and LSK 6R to send it to the DCDU.
When ATC responds, pay attention to the instruction because they will not just clear you to turn to the heading but also instruct whether they want you to turn left or right to the new heading.
Also you always need to check because the instruction may not exactly match what you are expecting to receive. You may in fact be instructed to a different heading to the one you requested.
Be careful when requesting headings. They are not always the most appropriate choice. Ground tracks are more accurate from the ATC perspective, because a ground track is always true.
For example, assume that you are told to fly heading 330 and you turn the aircraft so that the nose is pointing to 330, but you are moving forward at 240 knots and there is a wind gusting 40 knots at you from the southwest. Your heading will stay at 330 the entire time, but over time you will be more and more off course from the 330 radial you were steered onto at the start of the move due to effect of wind drift and the rotation of the Earth below you.
Ground tracks are useful when your RNAV is tuned to a VOR station and your autopilot is set to NAV mode. If you don't have a VOR to lock onto, then autopilot can be set to HDG and you set a heading instead of a ground track.
The AP works differently in these modes. When you are in HDG mode, the FMGS instructs the AP to keep locked on to the current compass heading. The compass tape will not move around unless you take a real hammering from wind or turbulence.
When you are in NAV mode, the FMGS instructs the AP to adjust your heading in order to remain on the desired ground track. If you have never experienced this AP effect before, you could be alarmed to see the compass tape moving about, but this is not a problem as long as the aircraft keeps moving forward along the correct ground track.
In other words, when in NAV mode, your nose does not necessarily point to where you are going, but to where it needs to point to in order to ensure you get to where you are going in the most efficient way.
Follow the same procedures involved in requesting a heading, but press LSK 3R instead of LSK3.