ELAC 2 No Dispatch A320
 

The Dispatch Deviation Guide for my company lists ELAC 2 as a no go item. ELAC 2 is suplied by the DC2 Bus and ELAC 1 and SEC 1 are powered by the DC ESS bus for operation in the EEC. All three have a standby power supply as either HOT 1 or HOT 2 so presumably all have a separate standby supply regardless of whether the AC network is supplied. I am led to believe by inference only that ELAC 2 is a no go because the flight controls need some power if the aircraft transitions to the EEC but if all three are powered by a Hot bus, I can't understand why ELAC 2 would be the no go and it's acceptable to dispatch without ELAC 1. I'm missing something I know but unfortunately the FCOM doesn't deal with it in sufficient detail. Can anyone provide me with the reason? I'm assuming that the my company's DDG is a straight transcript of the Airbus MMEL in this regard.

Hi, factsonly! I want to believe that I have found the solution.
The condition: We dispatch without ELAC2, the rest systems snd computers work properly. In that case the elevator is controled by the ELAC1 via the blue hydraulic jacks ONLY (FCOM1.27.10 p.6 and p.8).
In the flight, suddenly, the Blue hyd. system fault occures. The system does not shift pitch control to SEC 1 or SEC2. (FCOM 1.27.10 p.6 and p.5) because the ELAC 1 is still availiable.
Consecuence: we don't have alevator at all.
Correct me if any doubt, please!

Con respecto!

Been a while since I worked the 320 but elac 2 failue was definitey a no go item.MEL for elac 1 was 3 pages long or more and hardly worth the effort if spares were anywhere nearby.

Its been 20 years since I did the school but the priority I think for elevators was that elac 2 was the last resort.

sec 2, then sec 1, elac 1, then sec 2 (on blue hyd)?
maybe sec 2 elac 1 sec 1 then elac 2 ?

Like I said a loooong time ago and things can change but elac 2 definitely no go when I was on that type.

I could dust off the notes but by the time I did that someone current will answer the call.

Hi pensador,

I agree with your logic as FCOM is written.

Con respecto.

I think it's because, a single additional failure of Blue sys hyds, would cause ELAC 1 to fail on the elevator and give control to SEC2. So we have now lost half the elevator computers.

Elac 1
 

I think Pensador is right rudderrat - ELAC 1 doesn't fail (no change to electrical supply, just B hydraulic failure)
Cheers

Hi Paua,

Sorry for not being more specific - I mean ELAC 1 will fail to control the elevators when Blue Hyds is lost, then there will be an automatic transfer of control to SEC2.

In the same way that when ELAC2 fails to control the elevators with G + Y Hyds loss, then there's an automatic transfer of control to ELAC 1

Elac 1 available
 

Hi Rudderrudderrat
Could you please confirm the loss of Hydr OR Elec power to ELAC1 would cause control to be passed to the SEC?
We used to be told the ELAC1 wouldn't pass control if it was only Hydr fail and Elect was still available.
This is certainly not the case with ELAC2 (the loss of Hydr or Elect will cause ELAC1 to take over) so our info may well have been incorrect.
Regards, Paua

Hi Paua,

I have no other information about the way one computer passes control to the next. I assumed that they all worked in a similar way by passing control to the next when they recognised that they were ineffective. So if your information is correct - then pensador was spot on with his first post.

Hi Rudderudderat
I guess there is no reason to believe the conditions for handover from ELAC 1 should be different from ELAC 2.
Your suggestion would be the more logical in providing greater redundancy
Cheers :)

ELAC 2 No Go
 

:ok:ELAC 2 is no go since during the RAT extension in case of EEC, the ELAC 2 is the computer in charge of the pitch axis. During the RAT extension the Blue hydraulic power is not yet available and normal electrical power is lost, ELAC 1 can therefore not control the pitch axis of the aircraft during this phase.
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FYI, ELACs are equivallent computers (also applies to SEC computers) which means that if you get ELAC 2 fault before departure, the best and quickest solution is to swap the computers (ELAC 1 inop and ELAC 2 ok).

Cheers

Guess ain't that easy sir. It is important, when swapping or replacing computers, to strictly adhere to the mixability and interchangeability rules laid out in service bulletins and IPC. Two ELACS thought to be analogous, might belong to different standards though, thus leading to unexpected system operations.

fredgrav

Thanks for all the replies guys. I'm glad the thread started. To summarise, with ELAC 2 not available, in the event of a loss of the blue system through either system failure (e.g rupture) or loss of AC power, elevator control is lost until the blue system is powered again. ELAC 1 will not transfer control to SEC 2 unless it has failed electrically, even though SEC 2 always remains powered (through its associated HOT BUS) and in control of the L and R elevator through the B and G systems, it just can't "use" that authority because ELAC 1 still "has control" even though it has no way of asserting that control. Seems like a line of code could be written to tell ELAC 1 to surrender control in that situation but with feedback, it would probably take a few seconds to restructure the control path and Airbus get around it by simply making ELAC 2 the no -go.

Hello all,
My above comment was in fact the Airbus reply to the same question raised by me (thru my company) some years ago.

Regarding the mixing of F/CTL computers:
There is nothing called ELAC 1 or ELAC 2 but ELAC computer until it is fitted in the a/c. The slot, in avionics compt, where the computer has been plugged in will determine it's number. (the same applies to SECs)

Of course that is the case an elac is an elac.
but....
What fredgrav was saying is that not all elacs are the same.

The onboard software can be different and intermixabilty can change
Can be one way interchangeable or 2 way.
I think elac 1 and 2 must have the same OBRM fitted but never assume.Airbus compatibility and interchangeability can be quite complex.

I know some operators dont like swapping known U/S components into another slot lest damage be done.Especially very expensive items like flt ctl boxes.

Worth considering before you do a quick swap.

The U/S elac could be taken out because of what it talks to / damaged wiring etc and therefore placing a good one will render you U/S with 2 stuffed elacs.

Elac , Sec I/c
 

PN evolution is as well based on MODs / SBs implemented to the aircraft.
Therefore you will always be able to swap SECs or ELAC on your current aircraft.
You will have to look out for I/C when swapping boxes which come from another a/c as one can have an SB implemented the other one not.