A320 FMGS Computers "Flip-Flop"

[Microburst2002]

I can't remember where I read that if you switch on both FDs on within a few miliseconds the computers would "flip-flop" (whatever that is) and there would be a dual reset with loss of data or something like that.

However I have observed many crews during the cockpit preparation that always switch them on simultaneously, using both hands. I do it in sequence.

Any comments about this?
and, Does someone know what manual and page this flip flop thing is written?
thanks

[bflyer]

never had that

[Fly3]

I think most crews do it simultaneously to ensure that one isn't inadvertantly left on preventing the thrust switching to speed mode.

[kijangnim]

Greetings
The toggle switch on the MCDU switches the MCDU ONLY the FMS IS ALLWAYS ON unless you pull the circuit breakers.

For resets it depends uppon which FMS you are talking about, Legacy, Pegasus or FMS2 Thales/SI

[Microburst2002]

Computer ways are almost as misterious as God's.

I read it somewhere. Flip-flop when switching ON both FDs within x miliseconds.
But I see first officers using both hands and press the pushbuttons simultaneously during the cockpit preparation...

[TyroPicard]

I have always believed that you never ever operate switches simultaneously .. you might shut down both/two engines instead of just one.

Happened in a BAC 1-11 many years ago when someone closed both LP fuel cocks instead of turning off some Fuel Pumps.

And an A320 pilot switched both GEN switches OFF instead of turning the Packs ON after take-off.. (think that one through)

I'm fairly sure the list is endless. One switch at a time - that includes A320 FD.

[Microburst2002]

Had never heard of that airmanship rule, but it is very good.

Anyway the simultaneous FD ON pushing I have observed is done on the ground, during cockpit preparation.
I have noticed they try to do it as simultaneously as possible. I don't know why they do it like that.

Any of you has also read the flip-flop thing?

[TyroPicard]

Anyway the simultaneous FD OFF pushing I have observed is done on the ground, during cockpit preparation.

True, but pilots are creatures of habit... if you do it on the ground you will do it in the air. I am sure it's easier (and possibly quicker?) to do one at a time.
Small point, but surely it's FD ON during cockpit prep?

[Capriati]

Microburst 2002,
To give you my opinion on your question; I have never heard of this. It may be true or it may not.
Secondly; As you are aware this is a Tech Log. Your post starts with: ''I can't remember where I read that...''. This is hardly an appropriate way to start a discussion on a Tech Log. This sounds more like a rumour. I like to see this Tech Log as a clean, factual way of describing things.
Correct me if I'm wrong. After all, I'm a novice to the board.

Regards
Capriati

[TyroPicard]

Capriati
Your post has nothing of technical interest in it - why did you bother? As soon as you delete it, I will delete this post as well.
Regards
TP

[Microburst2002]

Yes, Tyro
I will edit accordingly.

Capriati
I just want to see if anyone knows. Anyhow, sooner or later I will find it. Then I will recover this thread

But I still hope someone will show up and throw a light on this. There are incredibly knowledgeable people around here, who don't mind to share some of it with us, the amateur scientist-engineers.

[Field In Sight]

FCOM 1.22.30 page 6.

If from (sic) AP/FDs off, FD2 then FD1, are engaged within 180 milliseconds (one computation cycle), a flip flop of master FMGC may occur.

FIS.

[Microburst2002]

Thank you FIS

I can't believe it was there all the time!

So, apparently the flip flop is the a change in master FMGC where no vertical mode is engaged nor A/THR mode displayed in the FMA (but is A/THR active?).

To solve it, engage V/S.
What about disengaging and engagin again?

Anyway, there is no point for a pilot to engage them simultaneously during teh cockpit prep doing a tai chi like movement.

I have another question for you:
if we engage FD1 and then FD2 within 180 ms, we'll we have a flop-flip instead? haha just kidding

[aristoclis]

As I read this note, I come to the conclusion that it makes sense in the air.
On the ground during cockpit preparation, I am pretty sure I 've done it simmoultaneously (tai chi movement) several times without any effect (I guess at least in some of them FD2 was the first to engage). But no A/THR nor vertical mode were applicable during that phase anyway.

[Microburst2002]

Hi, Aristoclis

I guess you engage them simultaneously during the cockpit prep because someone told you to do so.
I wonder if they gave you any reason for that.
If there is one, I will do the tai chi myself from then on.

I don't think there is a problem in doing it on ground from the point of view of the flip-flop thing, but who knows. Maybe its the reason for a later autothrust fault after take off or something.
In the air, there could be some scenario in which that flip-flop could occur and have bad consecuences.

[aristoclis]

Hello Microburst2002,

I do not recall anybody telling me about the importance to select or not to select both FDs simmoultaneously. Only to select either both or none, as stated in the manuals.
I encountered A/THR transient failure only once after take off. Don't know if FDs simmoultaneous selection contributed to it.
Anyhow, I don't see why not changing my habit and select the FDs ON with a short intervall. I like the "one at a time" theory better, even if it is just for FDs on the ground.

Regards.

[Metro man]

I used to select both on simultaniously until a line captain pointed out that FCOM passage to me. Flying with a training captain the other day they were selecting both on simultaniously, as we were getting ALT NAV instead of CLIMB NAV I pointed it out. I then switched the FDs on one at at time CLIMB NAV blue.

[Microburst2002]

Hi
ALT instead of CLB, you probably have an ALT SEL at or below ACCEL ALT.

Thank you all for your comments

[goeasy]

FD off after landing?

As a slight thread creep... do you switch off the FD's after landing? It seems to be SOP here without it being written anywhere. Never ever saw it in my previous company....

Any opinions for/against? Reasons?

[heggo48]

FD engagement

What you read is true and it exists....you will find it in the FCOM 1 (also known nowadays as DSC, it is under AUTOFLIGHT / FLIGHT GUIDANCE / FLIGHT DIRECTOR.....its a note in the flight director automatic disengagement and reads as follows:
If AP/FDs are OFF, and FD2 then FD1 are engaged within 180 ms (one computation cycle), a flip flop of master FMGC may occur.
As a result, no vertical mode engages, the FMA 1st column, 1st line (A/THR mode) is blank or displays dashes.
Engaging V/S mode manually re-selects the correct FMGC and restores the display.

now for the explanation....flip flop means a reversal in the function of the FGMC concerning the MASTER-SLAVE logic between FMGC1 and FMGC2....meaning that that FMGC1 goes from master to slave and back, and the opposite occures with FMGC2 (slave to master and back).and as a concequence, the Aircraft system gets confused and doesn't know which FMGC is MASTER and should control the A/THR which merely inhibits the engagement of normal vertical modes and auto-thrust, that's of course confusing and inconvenient for flight crews, and even sometimes hazardous depending on the flight phase this flip-flop occurs.

Its worth noting that flip-flops do not cause loss of data from FMGC.
hope this was of help.
cheers