View Full Version : Airbus A320 Tech question

4th Jun 2003, 07:32
Why does an LGCIU1 failure render render Reverser 1 inop?

Hand Solo
4th Jun 2003, 08:03
Starter for ten.....

Is it because LGCIU 1 is linked to the air-ground switch which prevents reverser 1 being deployed in flight? Which may also be linked to the requirement to switch off the GPWS because it can't tell if the gear is locked down?

Jet II
4th Jun 2003, 15:49

10/10 - Reverser actuation logic requires the onside LGCIU to give a main gear compressed signal.

4th Jun 2003, 16:37
are you sure that's the reason? lgciu 1 doesn't just handle the left l/g if that is what is implied

5th Jun 2003, 18:38
Hand Solo and Jet II have it right - LGCIU 1 sends on ground/in flight signals to various services around the aeroplane. In the event of a failure of LGCIU 1, some users will see a "flight" condition, and some will see a "ground" condition. Whether things see flight or a ground condition is dependant on whether it's a proximity detector that's failed or it's an electrical failure of the LGCIU itself. See FCOM 1.32.10 p5.

In either case, the FADEC on the relevant side will see a flight condition, and thus will inhibit reverse on that side, along with a few other things. FCOM 1.32.10 pages 6 and 14 refer.


Tonic Please
7th Jun 2003, 19:49
I am quite interested to understand the abbreviations in this thread. I am not by any means technical at this level, and would be interested if someone could explain the question to me, so I understand what is being said :)

SMooth skies,

7th Jun 2003, 23:56
No problem!

LGCIU - Landing Gear Control Interface Unit. The aircraft has 2 of these. These are the "brains" of the landing gear system. They give orders and information to bits of the areoplane that need it about the what the landing gear is doing. ie is it up/down/unlocked etc. Also they sequence the movement of the landing gear itself. Amongst other things!

GPWS - Ground Proximity Warning System. Every commercial aircraft has one and it does exactly what it says on the tin - warns the crew of ground in close proximity. Some give warning of ground ahead of the aircraft (Enhanced GPWS), but most only look down not forwards.

FADEC - Full Authority Digital Engine Control. Each engine has one. Basically an advanced version of what's in most posh cars these days. It basically looks after and controls the engine and all it's parameters.

FCOM - Flight Crew Operating Manual. The Airbus acronym for the aircraft's technical manuals. There are 4 in the series - all cover different things.

The original question related to why the Number 1 (left-side) reverser (the part of the engine that provides reverse thrust for braking after landing) doesn't work when LGCIU 1 doesn't work. The answer is that for the reverse thrust to work, the FADEC (which controls reverse thrust for its individual engine) must receive a signal from LGCIU 1 that the left main landing gear is on the ground. This is to make sure that reverse thrust can never happen in the air - the aircraft would possibly crash if it did. However, when LGCIU 1 doesn't work, the FADEC on engine 1 doesn't get that signal and therefore will not allow reverse thrust on that engine because it doesn't know that the aircraft has landed. All about safety really.

Hope that helps and is not too long-winded!!!


Tonic Please
8th Jun 2003, 01:16
Fantastic reply and easy to understand. Much appreciated...I have been interested in aviation since 3, and ever since up to 18 and a half years old, I have read aviation, aircraft. Got PPL etc, but you'll always find me reading some ATPL syllabus level material, or aircraft specific material. That is why this interested me. I like to be intelligent you see ;) No point living without knmowledge of some kind.

Smooth skies, thanks again...


8th Jun 2003, 13:04
:O and it always helps for chatting up the ladies in the bar!...or is that boring them to tears in the bar...I always get that mxed up ;)

Tonic Please
8th Jun 2003, 17:09
I'm taken with an amazing girl, so you wont find me chatting up at the bar. I think its boring them to tears. I once got talkin about the approach into Heathrow when I saw a virgin 340, but I stopped after a couple seconds. Think I would be down the bar chatting up if I didnt stop :}

12th Jun 2003, 11:48
LGCIU1 failure does NOT render Reverser 1 inop. First of all the FADEC is not involved in the reverser depolyment, only in the power setting of the engine. The On-Side EIU(Engine interface unit) recieves the revers signal from the Thrust potentiometer, it then checks for groung signal, first from onside LGCIU, if that is missing it uses Off side plus Radio alt and/or Wheel speed if all these conditions are fullfilled then it checks for Revers confirmation signal from SEC(spoiler elevator computer)then it sends a revers deploy signal to the HMU, when it recieves revers deployed more than 90% it lets the FADEC increase thrust.

Tonic Please
12th Jun 2003, 15:46
:ooh: Let me read that again

12th Jun 2003, 18:06
OK, well in that case, why does the FCOM on page 1.32.10 p14 say:


A/c in flight (when either LGCIU output indicates flight) - Reverse inhibited

A/c on ground (when BOTH LGCIU outputs indicate ground) - Reverse available"

The way I read that is that BOTH outputs of the LGCIU have to see a ground condition for reverse not to be inhibited on that side, each LGCIU having 2 outputs.

It also says :

"The FADEC system performs the following functions:

Thrust reverser control - actuation of the blocker doors
- engine setting during reverser operation"

"FADEC, also called the EEC, is a digital control system that performs complete engine management"

FCOM 1.70.20 p1 and p4 refer.

Either way - you cannot get away from the fact that with an LGCIU inoperative - reverse IS lost on the that side. I know that because it says it in the FCOM, I've had it in the sim and on the aircraft - it DOES happen.

Cheers all

Jet II
12th Jun 2003, 19:14
Airbus Operations Manual A320 IAE

Reverser Actuation Logic - 12-70-75-2

Deployment requires:

One FADEC channel operating with its associated throttle reverse signal
Right and left main gear compressed signals from the corresponding LGCIU's
A Thrust Lever angle (TLA) reverse signal from at least one Spoiler Elevator Computer (SEC)

Before the deployment is completed, the FADEC sets reverse idle thrust on the engine that is having its thrust reversed.


13th Jun 2003, 01:39
Remember that FCOM means FLIGHT CREW Operating Manual.

What is written in those manuals are quite often lacking detailed information on how a system is designed and works.

If you want to know how to operate a system they are fine but if you want to know how a system works they are not.

I suspect that the Doc has access to the MM and WDM.

13th Jun 2003, 01:48
I'm sure Airbus would be glad to hear that their manuals are so poor!!!!!

Look, at the end of the day you DO lose Reverser 1 when LGCIU 1 is inoperative - I've had it on the REAL AEROPLANE - it DOES happen!!!!!!!!!!!!!!!!!!

I'm sorry but I just can't accept that the Maintenance Manual and the FCOM would be different, which is effectively what you are saying! What the Doc has said is just plain wrong according to my A320 FCOMs. Maybe the MM is more detailed yes, but different - no way!!!!!!!!!!!!!!!

13th Jun 2003, 03:25
What I am saying is that your manuals are exactly what it says on the cover, Flight Crew OPERATING manuals.

With regards to the technical description of the aeroplane they are full of generalizations and simplifications.

It is not uncommon to see only the major components of a system described and assigned functions, which in reality are carried out by one of the many other components in the system that are not included in the description.

All in the name of simplicity.

And not only in that respect is the MM different fom the FCOM, it will also differ in operating techniques and limitations.

To give you an idea of how simplified they are, I can tell you that I have taken the computerized test in a couple of the systems and passed. Without any training or knowledge of the A320 I passed tests which I assume are based on information coming from the FCOM. I might just have been lucky, but I doubt it.:8

14th Jun 2003, 20:59
Well this one got me going! Had to have a look at the manuals to check!

SLT is quite right LGCIU #1 fail will cause T/R #1 fail. I have had it too, as a line defect (I am an engineer). And the simple reason is that the onside LGCIU controls the reverser actuation logic.

The complicated answer is a bit more involved (aren't they always :rolleyes: )

Doc is I am afraid wrong. He is also right :ooh: . Let me explain

The onside Engine Interface Unit (EIU) provides actuation logic for the T/R based on Throttle Lever Angle (TLA) less than 3 degs (This info comes from the SEC's) and a/c on the ground (from the onside LGCIU) If the conditions are met then an inhibit relay is activated. This relay then allows the FADEC ECU to control the operation of the reverser itself, provided that the T/R isolation valve (hydraulic valve) is open (this valve opens when SEC's 'see' reverse commanded and a/c on ground or less than 10 foot RA)

However, the be all and end all is that a failure of a LGCIU will result in loss of the onside reverser.

Hope this helps.

15th Jun 2003, 00:53
Hi Mono,
I just had a look at my traing manuals and then the AMM, and guess what, we are both right.
On the CFM powered A/C WITHOUT SB 320/78-12b incorborated it is true that on side LGCIU failure will cause onside Reverser to be locked out, post mod, the command LGCIU will give the GND logic to both EIU's.
You are right about the actuation logic, it has been a while since I was working with that sys in depht and was going by my teflon memory(nothing sticks)

Tonic Please
15th Jun 2003, 20:38
Could you translate that quote from the A320 AMM into English by any chance?

Thanks :}

(im following this post you see. I am interested in all the complicated stuff if thats ok)...

18th Jun 2003, 08:02
Well, I never expected a simple question to spark off such a heated debate!

The reason I asked was that I had an LGCIU1 fail (IAE 320) and on ECAM, REV1 was listed as inop. I was both knackered and not within reach of a tech manual, so I was hoping for the answer.

Thanks, SLT and others, it's all coming back to me! Best I get back in the manuals!:O

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