OEB Alpha Prot

[tubby linton]

in the early model A320s it was not uncommon to see a status message displayed without any associated warning or caution. The message was always Cat 3 dual inop. It took a bit of digging in tne manuals to discover that this related to an ADR disagree. After a few years these messages stopped appearing and. I have not seen one for at least ten years.

[vilas]

tubby linton
It is level 1 caution. It is loss of redundancy or system degradation, only requires crew monitoring. It is a caution message without procedure. It is still the same.

[Microburst2002]

CONF iture

You are totally right!

The system of voting a computer when the other two agree can have potentially lethal results, and therefore it should be indicated to the crew when this happens, so that some procedure allows us to make sure that the voting of a computer is correct. if computers alone cannot do it, get the pilot involved in the process. No reason to keep it "transparent to the pilot".

THe ECAM you suggest should be accompanied by an AOA CHECK PROC APPLY blue line, or something like that.

[A33Zab]

NAV AOA DISCREPANCY

A 'xxx DISCREPANCY' message is used if one display deviates from the other display.
e.g. NAV ATT DISCREPANCY or NAV IAS DISCREPANCY.

Latest standard A330 do have a NAV AOA DISAGREE msg but only if ALL AOA disagrees or
(after EFCS rejection of one) the - Cz estimation - on the other 2 deviates.

Don't know if this also applies to A320 and what 'Cz' estimation here exactly means.

But in this case displays were in agreement as was the value of AOA1 and AOA2 hence messages would not have triggered.

[CONF iture]

Discrepancy, disagreement, ... this is a topic for discussion when time permits but in the middle of the night all a crew wants to know is that something's going on with the AOA data and prepare accordingly before some protection could mess around ...

[tubby linton]

Vilas, it was not a level one. The only message was on status ,and it appeared as an inop.

[Lantirn]

A3Zab,

I think there was in A320 older msn's the NAV AOA DISAGREE msg, but not sure.

Newer versions have the NAV ADR DISAGREE msg which includes speed or alpha disagreement. However I thought that for this msg to come up would require an ADR firstly to have been failed or rejected by ELACs.

As for the DISCREPANCY msges, I am new in the bus, FCOM doesn't clarify this but makes a lot of sense. Do you know the tolerances for the IAS msg between PFD's? Thanks

[Microburst2002]

A330
the NAV ADR DISAGREE (or the NAV AOA DISAGREE depending on the model) caution is necessary when one of the three ADR was already declared faulty or it was switched OFF and there is a disagreement between the two remaining ADRs (or AOAs, depending on the model).

This caution does not protect us from a treacherous failure of two ADRs or AOAs in such a way that their error is coincident and it has the effect of declaring faulty the only healthy ADR. It is a necessary caution, since with only two ADRs there is no possible voting.

What protects us is that, every time an ADR is declared faulty we have to be healthily paranoid and check that it is OK that ADR #x has been correctly rejected (or not). All the more if the reason of the rejection is a disagreement of one versus the other two. That is why I would appreciate to get that information.

Now I think that the best way to give this info could be a extra line below the NAV ADR FAULT caution (something like DUE ADR DISAGREE?) when the reason of rejecting is the result of a voting.

[CONF iture]

Bangalore

Originally Posted by vilas

In IA crash pilots switched to open descent without realising it and speed kept dropping finally 27 Kts. below Vapp. One pilot switched off his FD without other pilots knowledge. All the time they thought they are in speed mode but no one checked the FMA, there was not a single call about speed by any of them. Finally alpha floor did kick in and also pilots themselves moved to TOGA but they lost their lives because they did it 15 seconds too late.

Actually they were well aware to be in open descent but didn't know how they ended up in such mode they did not desire. Instead of minding the overall situation and mainly the speed they put their energy on finding why they were on that OP DES mode and how they could leave it.
Instead of reverting to the fully manual solution, they were looking for a software solution (is it a consequence of the training where emphasis was probably more on understanding and managing a computerized system ... ?) but could not find it on such short notice for a System that was new for them.
For guys with their experience on HS748 and B737 it is surprising how they simply forgot about checking their speed, or how one can be easily distracted ...

[vilas]

Problem happened below 500ft. They had asked for visual approach how does it matter which aircraft or mode you are in. You just maintain speed and flight path angle and land. SFO and Bangalore both aircraft were flown visually without looking at speed. In SFO the conventional yoke, active feed back, Q feel, moving throttles but when basic norms are ignored or are absent nothing helps.

[A33Zab]

@Latirn:

Do you know the tolerances for the IAS msg between PFD's?

IIRC it is 16kt for ?? sec. as detected by PRIM (FCPC) or if 'Pitot-icing' is detected (fast drop of Pt) by FCDC.

[Lantirn]

So the tolerance is the same as the discrepancy msg.
16kts or 0,05mach for 10secs.

Thank you

[CONF iture]

Originally Posted by vilas

Problem happened below 500ft. They had asked for visual approach how does it matter which aircraft or mode you are in.

It matters so much that they have crashed.
They had no problem managing the basic only 6 months before but suddenly forget about it after acceding to the latest technology. It only tells that something big has been missing during the training for the transition.

[Denti]

Indeed, the golden rules are probably briefly noted, but the real importance of them seems to be usually lost, especially rule 1 and 2. And that is certainly a lack of the right training.

[A33Zab]

@OK465:

Thx for confirmation.

@ CONF iture / Microburst2002:

Discrepancy, disagreement, ... this is a topic for discussion when time permits

We have all the time here....

but in the middle of the night all a crew wants to know is that something's going on with the AOA data and prepare accordingly before some protection could mess around ...

That is why I would appreciate to get that information.

That's exactly what OEB 48(SR)/49(LR) and (previously OEB 45) is all about, Anticipate->Monitor->Prevent and Recover if the first 3 have been missed.

[b215]

Hi tubby,
I still see this in late msn A/C, usually in turbulence status msg shows Cat 3 single only/ inop sys Cat 3 dual. Indeed due to adiru disagreement.

[CONF iture]

Originally Posted by A33Zab

That's exactly what OEB 48(SR)/49(LR) and (previously OEB 45) is all about, Anticipate->Monitor->Prevent and Recover if the first 3 have been missed.

As the System already knows something is incorrect with primary data, why shouldn't it simply inform the crew ... ?
Anticipation part done !

... but then you can only publish a red OEB and put everything on the concierge's shoulders ...

[vilas]

The self identified ADR failure cannot be simulated. To give ADR disagree scenario you need to fail one which is indicated to the crew before making other two disagree .

[tubby linton]

Thank you for your post b215. I have only ever seen it in an A320 not in an A321.

[vilas]

In 16th Operational and Performance Conference Airbus had indicated a change to ECAM alert NAV AOA DISAGREE and in status page they added RISK OF UNDUE STALL WARNING. It was supposed to be effective in FWC H2F5 MOD 37871 date of completion Jun 2009.