Airbus A320 GPS and navigation display VOR

[AF330]

Hi!

1) Could anyone explain me where the GPS signals goes after the MMR?

2) I imagine that it goes to the FMGS to calculate. So does the FMGS sends the next step (he knows where we are with the GPS) to the F/D which sends it to the A/P which sends it to the ELAC computer, right?

3) But I imagine that it won't be the same "route" in selective mode (or if FMGS has failed). So which computer decides in selective mode the next step? Is it the ELAC? So basically A/P is sending to the ELAC what we have entered in the FCU and ELAC is receiving data from the GPS so it knows what to do to satisfy our demand? But in managed mode, the FMGS calculates the next step not the ELAC...

Check this please:

http://theflyingengineer.files.wordpress.com/2011/11/16.jpg


3) Here we can see VOR2. Airbus autotunes VOR's and we can enter it in the RAD NAV page of the FMGC. Just one question: When it autotunes or when we enter VOR1, does it use the VOR antenna's to display it? Or is it the GPS that sends the position to the FMGS that calculates on which CRS of the VOR we are? Because, in any case, when we enter a TRK/CRS and the frequency of a VOR, it still uses GPS (GPS sends signal to the MMR which sends signal to the FMGS, then to the F/D, to the A/P and the ELAC computer and finally to the hydraulic jack)

Please help!

[AF330]

Ok... No, let me ask the question this way:

First I would like to confirm this:

1) The VOR 1 and VOR2 displayed on that photo are coming from the VOR antenna. So when we see VOR1 ---, it means that the VOR is not in the range of what can "see" the antenna.
2) We say to the ELAC: we are here. We want to go there. Right?

Now comes my question: when we enter a CRS and the frequency of the VOR, we tell the plane that we want to be in this radial of this VOR. ELAC knows where we are (GPS) but it should know where is the VOR. Because when we enter x HDG, it means that we want to be HDG x from where we are. So the ELAC knows where we are.

So for a CRS, is the antenna VOR connected with the ELAC to tell him? Or has airbus peogrammed each and every VOR in ELAC so that it knows directly where to go?

Thanks

[MD83FO]

Hi..

the moving map screen you see on the A320 comes from IRU inertial reference units using inertial information (coordinates), it fine tunes itself using GPS or VOR or DME in that order, which are all independent sources of navigation, but inertial is the boss.

the bearing pointers (needles) on the screen are using VOR or NDB information only from ground stations.

If you want to fly to a VOR you can select a HDG to it using the needles or you can type it on the MCDU or FMC and the airplane will fly there using inertial reference (coordinates) with a back up from GPS, VOR or DME.

sometimes the map is wrong and you have to use the old system of VORs.

the MMR and all nav info goes to the FMGC (autopilot/ flight director) then the FMGC talks to the ELAC which moves the flight controls of the plane.
I think this is the level of understanding that you have hope it is helpfull.

[AF330]

Hi! Thanks a lot!
Don't know IRU! What is this exactly? How does it know where we are exactly? Is there an IRU antenna or something?

So IRU is the boss, then you have GPS, and then IRS, right?
Coordinates? Is there an IRU computer which knows each and every coordinate? Or is it the GPS which is giving our position to the IRU? IRU is only used to display our position or something else too? Navigation?

Everyone had said that there were only 2 things: GPS with backup IRS!

Thanks to clear my doubts!

[AF330]

Wiki: The*IR
*component of an ADIRU gives attitude, flight path vector, ground speed and positional data.The*ring laser gyroscope*is a core enabling technology in the system, and is used together with*accelerometers,*GPS *and other sensors to provide raw data.
The primary benefits of a ring laser over older mechanical*gyroscopesare that there are no moving parts, it is rugged and lightweight, frictionless and does not resist a change in*precession."

Is IRU = GPS + IRS?

[TopBunk]

The Air Data and Inertial Reference System (ADIRS) supplies temperature, anemometric, barometric and inertial parameters to the EFIS system (PFD and ND) and to other user systems (FMGC , FADEC, ELAC, SEC, FAC, FWC, SFCC, ATC, GPWS, CFDIU, CPC).
The system includes :
– three identical ADIRU’s (Air Data and Inertial Reference Units).
Each ADIRU is divided in two parts, either of which can work separately in case of failure in the other :
• the ADR part (Air Data Reference) which supplies barometric altitude, airspeed, mach, angle of attack, temperature and overspeed warnings.
• the IR part (Inertial Reference) which supplies attitude, flight path vector, track, heading, accelerations, angular rates, ground speed and aircraft position.
Note: Above 73 North and above 60 South, the ADIRU gives true heading
instead of magnetic heading.
– one ADIRS control panel (ADIRS CDU) on the overhead panel for selection of modes (NAV, ATT, OFF) and indications of failures.
The IR is normally initialized through the FMGS, but the ADIRS CDU may be used as a back up.
– four types of sensors :
• pitot probes (3)
• static pressure probes (STAT) (6)
• angle of attack sensors (AOA) (3)
• total air temperature probes (TAT) (2)
These sensors are electrically heated to prevent from icing up.
– eight ADMs (Air Data Modules) which convert pneumatic data from PITOT and STAT probes into numerical data for the ADIRUs.
– a switching facility for selecting ADR3 or IR3 for instrument displays in case of ADIRU 1 or 2 failure.

Separately.

The aircraft has two independent GPS receivers. Each GPS receiver is integrated in a modular avionics unit called MMR (Multi Mode Receiver) (GPS 1 receiver in MMR1, GPS2 receiver in MMR2).
The MMR processes the data received and transfers them to the ADIRUs, which then perform a GP-IRS hybrid position calculation. The FMGCs use the hybrid position. The GPS MONITOR page on MCDU1 or MCDU2 can display pure GPS position, true track, ground speed, estimated position, accuracy level, and mode of operation for the information and use of the flight crew.
Note: Flight crew can use the MCDU NAVAID page to deselect the use of GPS data for calculating position

[TopBunk]

In the 'old old' days before INS came along, we had conventional instruments that used various gyroscopes and dynamic and static pressure to present attitude, altitude, heading, vertical speed and turn & slip information to the pilots. This basic instrumentatiom was supplemented by navigation techniques using VOR's, DME, ADF, radar, astral navigation, doppler, Loran etc to determine position - we used to navigate around the world like this!

The along came INS (Inertial Navigation system). This used 3 gyros set in a box at 90 deg to each other which sensed gravity and could work out where you were on the planet. Once it knew where you were, it sensed acceleration in the 3 different gyros to work out your vector in 3D and could therefore work out where you were now - the difference between position a and b representing the vector (up/down, left/right, faster/slower) which it translated to attitude, heading, airspeed, groundspeed, VS and position information. You could load about 9 waypoints (manually by lat/long) and it would command the AP to take you there. As you passed a waypoint you had to add another to keep going where you wanted to go - time consuming and prone to error.

Then along came FMS capability to store flight plans, navaids, airports and airways etc which you loaded and a whole route could be established.

All that has happened since is to further refine the information acuracy. We now have IRU to replace INS - better gyro technology basically. Air Data sources are fundamentally unchanged, although digital processing is better. GPS merely adds another (albeit it very accurate) source of position information. As such it is secondary to the (AD)IRUs in the hierarchy.

This is not meant as an absolute definitive history but to try and show how history has evolved.

[AF330]

Ok so here is the route:

1) GPS- MMR-ADIRU-FMGS. IRS/INS/INU are backups, right?

2) ADIRS is devided in ADR and IR. Both have different sensors which provide informations. Right?

3) What do you mean by GP-IRS?? GPS + IRS? But GPS is primary.

Let's first clear this to continue...

[FlightDetent]

AF330: sorry, not possible. Your assumptions draw the debate out of tech log.
I really do apologize, but as I see it, you mix apples with camshafts.

But please, keep the enthusiasm going, just wait before playing a game of chess until you are ready to differentiate between what is the board, figures, and the players.


PS: You live in Paris?

[AF330]

Ok, but I will still wait, hoping for answers!

And yes, I live in Paris, France. Why? ;)

[spannersatcx]

Ok so here is the route:

1) GPS- MMR-ADIRU-FMGS. IRS/INS/INU are backups, right?

no - re read what topbunk has told you.

[FlightDetent]

It is a lovely city, I envy you :)

[AF330]

@Flight Detent: Ha ha! Yes, indeed, it's a great city! I have also been to Prague (you live there, no?). It is great! Loved the Prague castle and the night walk over the Charles Bridge! One of the best cities I have been in Europe! ;)

"The aircraft has two independent GPS receivers. Each GPS receiver is integrated in a modular avionics unit called MMR (Multi Mode Receiver) (GPS 1 receiver in MMR1, GPS2 receiver in MMR2).
The MMR processes the data received and transfers them to the ADIRUs"

2 GPS receives data. The GPS is inside the MMR. Then the MMR sends the position to the ADIRU.

"....which then perform a GP-IRS hybrid position calculation."

Ah! So GPS is just giving the position, IRS/INS/IRU is capable to calculate the time:
"We now have IRU to replace INS - better gyro technology basically. Air Data sources are fundamentally unchanged, although digital processing is better. GPS merely adds another (albeit it very accurate) source of position information."

Ok so GPS (MMR) +IRS signals (which is capable to calculate with gyro technology the position and the time which the signal will take to reach IR) send their signal to the IR. They get "mixed" and IR (part of ADIRU) figures out our exact position (which is normally the one sent by the IRS/IRU/INS).

It then goes to the FMGS.

Sounds good? ;)

[MD83FO]

you can download the FMGS manual here

A319 320 321 FMGS (http://www.smartcockpit.com/aircraft-ressources/A319-320-321_FMGS.html)

not for operational use,

all the info you're asking about is there.

[AF330]

Thanks!

1) What is an "hybrid position"?

So basically IRS/INS choses the data of one of the GPS'?

[MD83FO]

hybrid is when two become one, in this case, GPS complements inertial reference, to become one hybrid.

[AF330]

So IRS+GPS= IR? (part of ADIRU so the ADIRS)

Thanks...

[MD83FO]

it doesn't become one system.

its tow separate systems which are used for one purpose.
hybrid GPIRS, if GPS is not working inertial keeps doing its job.

[AF330]

Hmmm....
F-COM says that 3 IRS signals (3 position) come to the FMGS. And then FMGS calculates IRS MIX position. IRS doesn't need satellites. I can understand till here.

But then they talk about GPS position. They say that IRS choses one of the GPS signals which makes it GPIRS!!! Didn't get this one. The IRS choses one of the GPS?? But why? They are 2 different systems to calculate position!

Thanks...

[TopBunk]

AF330

I think part of your mis understanding is the meaning of GPS PRIMARY.

It does not mean that GPS is number 1 and used to determine everything, but just that the GPS position going into the mix IRS/GPS position (GPIRS) complies with an integrity criteria - a reasonableness check.

If it does not comply, then GPS PRIMARY LOST is displayed.

When it again complies, then GPS PRIMARY is redisplayed.


Again, historically, aircraft had been certified without GPS and GPS was the new kid on the block - a bit like you! It was not 'trusted' and was used to supplement existing navigation methods, hence the crew retain to this day the ability to deselect GPS as an input to the navigation processes. Indeed the national governments that put up the satellites retained control over them and could 'modify' the positions they provided to deliberately create inaccuracies for their enemies - remember the satellite network was originally for the military, and you don't want your enemy to be able to use your system against you to accurately bomb targets!

[AF330]

Thanks a lot, so do they get "mixed" inside the FMGS? Does it get mixed with the IRS MIX position? Or each position given by the 3 IRS? And when we align IRS, it takes 6 minutes!! Why and what does it do exactly? Because we are not moving, so how does he figure out our position?

[TURIN]

Ok I'll have a go.

The IRS takes as long as it needs to 'align'. Typically between 7 & 15 mins. That is, to settle down and become stable in it's present attitude and velocity. (Don't forget, the planet is rotating and the whole assembly needs to compensate for that).
So, when the internal magic of the IRS has done it's stuff and calculated it's attitude and stable condition, only then can the IRS be programmed to it's current position.
This is either done manually by the operator (pilot/engineer) by typing in to the scratch pad of the MCDU the Lat/Lon position.
EG 51.477.5 N , 00.461.4 W

Or by using a pre programmed position such as a particular gate at a particular airfield.
EG. EGLL gate 58

Alternatively, the IRS can be programmed with it's last known position OR it can use GPS (if fitted) to update the position in real time. As GPS becomes trusted more and more, this seems to be the favoured option.

Well, that is the way I understand it as a mere A&C. :O

[TopBunk]

AF330

We applaud your quest for knowledge. We have answered your original questions patiently. The thread is now drifting like a Schuler Loop - google that one - it is related!

Time to do some of your own research.

I'm out of here

[FE Hoppy]

The IRS can figure out our latitude without any external input. It cannot figure out the longitude. This we have to give it. We in fact give it both.



The earth is revolving. The IRS is sensitive to all acceleration so it can feel the acceleration around the earths axis. This is of course the axis between true north and south. So by measuring it's speed through space it can work out it's distance from the axis or rotation, i.e. it's latitude on the surface of the earth.


If it is sitting on the equator the speed through space would be fast and therefore the forces it feels strong.
If its sitting very close to the north or south pole the speed through space would be slow and the forces weak. Too close and it's not sensitive to align at all.

The alignment phase is really only finding out where the North south axis is. We then tell it what the longitude is.

When it knows lat and long and is aligned any new accelerations are converted to velocity of the aircraft and the position updated.

IRS 101

[TURIN]

I forgot about that bit FE H. :ok:

That's why I remain B1-1 (restricted). :O

[AF330]

Yes you all are right, just would like to confirm this and let's finish the thread.
A big thanks to MD83FO, Fe Hoppy, Top Bunk and Turin!

Just want to confirm this: 3 IRS send their signals to the FMGS with the position of the aircraft. The GPS does the same thing. The FMGS calculates the IRS MIX position. Then the GPS position and the IRS MIX position get "mixed" inside the FMGS and it calculates an hybrid position. Everything right?

Thanks a lot.

[MD83FO]

that sounds about right and you're welcomed AF

[AF330]

Thanks,

After some researches, I read all the posts back, and just had one more doubt:

So TopBunk had said:

"The aircraft has two independent GPS receivers. Each GPS receiver is integrated in a modular avionics unit called MMR (Multi Mode Receiver) (GPS 1 receiver in MMR1, GPS2 receiver in MMR2).
The MMR processes the data received and transfers them to the ADIRUs, which then perform a GP-IRS hybrid position calculation."

But you confirmed MD83FO that the GPS and IRS MIX position was mixed inside the FMGS. But TopBunk said that the hybrid GP-IRS position was calculated in the ADIRUs.

So:

1) Where does the IRS MIX position get calculated? In the FMGS or the ADIRUs?

2) Where does the hybrid GPIRS position get calculated? In the FMGS or the ADIRUs?

Thanks,