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grrowler
21st Aug 2015, 05:15
Just trying to get some greater understanding of this system, hopefully someone with more than my basic knowledge can help ;)

In the event that probe/ sensor blockages cause a dual ADR fault, the ECAM instructs us to turn off the affected ADRs, and the aircraft reverts to ALTN LAW.

Hypothetically, if the blockage/s were cleared, could the ADR's be turned back on, and would the affected systems recover? Any references would be appreciated:ok:

ACMS
21st Aug 2015, 09:54
Yes you can turn them back on but you won't get out of Altn 2 Law.

ACMS
21st Aug 2015, 10:08
From the A330 FCTM-----

TWO ADR OUTPUTS ARE ERRONEOUS, BUT DIFFERENT, AND THE REMAINING ADR IS CORRECT, OR IF ALL THREE ADRS ARE ERRONEOUS, BUT DIFFERENT :

Both the AP and A/THR disconnect. If the disagree lasts for more than 10 s, the PRIMs trigger the NAV ADR DISAGREE“ECAM caution.
The flight controls revert to ALTN 2 law.
The high speed protection and low speed protection are lost.
On both PFDs: ‐ The SPD LIM flag appears ‐ No VLS and no VSW is displayed

This situation is latched for the remainder of the flight, until the PRIMs are reset on ground, without any hydraulic pressure. However, if the anomaly is only transient, the AP and the A/THR can be re-engaged when the disagree disappears.

Southpole
21st Aug 2015, 10:09
I am going by heart because I do not have the book here, but the ADR once is off cannot be reset..

CX-HOR
21st Aug 2015, 10:10
However you won't know the result until you turn them back on, so it is not recommended. The voting logic might cause some very unintended consequences if it (ADR) was still faulty.

Better the devil you know some would say.

grrowler
21st Aug 2015, 10:57
Acms, thanks - think that pretty much answers it.

ahramin
21st Aug 2015, 23:09
Southpole maybe you are thinking of the IRS. The ADRs can indeed be switched back on.

grrowler
21st Aug 2015, 23:48
So just to clarify, if the ADR fault/ Disagree issue was resolved you could turn the ADR's back on. This would give you back AP and ATHR, but the aircraft would remain in ALTN 2. In this situation, the PRIMs could NOT be reset in accordance with the Computer Reset Table in an attempt to recover further systems, as the fault is latched. Is this correct?

ACMS
22nd Aug 2015, 01:45
Yes they can be turned on but as said above you'd have to be pretty sure their data would now be correct as it could make things a lot worse if it's wrong.

The Flight controls will stay in Altn 2 as its latched as I posted. You probably won't get the autopilot or autothrust back. It's an Airbus so anything so possible.

Don't reset the Prims, it won't help anyway.

vilas
22nd Aug 2015, 03:17
grrowler
In the event that probe/ sensor blockages cause a dual ADR fault, the ECAM instructs us to turn off the affected ADRs, and the aircraft reverts to ALTN LAW.

Hypothetically, if the blockage/s were cleared, could the ADR's be turned back on, and would the affected systems recover? Any references would be appreciated:ok:
If you had dual ADR fault and you switched off the faulty ADRs there is simply no way of knowing if the ADR has become OK. So end of story. The other case is NAV ADR disagree where one ADR is already rejected and other two disagree or all three give different outputs right or wrong immaterial you are asked to identify the faulty one/ones, there also once you switch off there is no way off knowing if it becomes OK. So your hypothesis is not very practical but theoretically it can be turned on, but when you don't know whether they are correct why would you?

grrowler
24th Aug 2015, 02:06
Thanks vilas and everyone, I appreciate it is a bad idea to turn back on ADR's that you are unsure if still faulty. My question was more about the system recovery if they were fine and you were to turn them back on.

My scenario given above is probably not that clear or practical - I've had a bit more of a think and I'll try another one, in conjunction with this excerpt from the FCTM:

IN-SERVICE EXPERIENCE OF HIGH ALTITUDE PITOT OBSTRUCTIONS
Analysis of the in-service events shows that:
- The majority of unreliable speed events at low altitude are permanent situations, due to the obstruction of pitot probes by rain, severe icing, or foreign objects (refer to the table above).
- At high altitude, typically above FL250, the cases of unreliable speed situation are mostly a temporary phenomenon: They are usually due to contamination of the pitots, by water or ice, in particular meteorological conditions. In-service experience shows that such a contamination typically disappears after few minutes, allowing to recover normal speed indications.

Let's say we are climbing through a layer of severe icing and the speeds go haywire. We apply the UNRELIABLE SPEED INDIC/ ADR CHECK PROC up to and including turning off 2 ADR's. We then clear the icing and do not expect further icing for the remainder of the flight. Do we continue like this until through FL250 on descent, turn off the last ADR and fly the BUSS, or could we while at a safe altitude, have a look at turning some ADR's back on?

If so, how would the systems recover?

vilas
24th Aug 2015, 02:55
According to ADR check procedure you either switch off two faulty ones and use the good one or if all are bad switch off all three below 250 and change to BUSS and land. The icing may clear and may not be expected later but there is no way of knowing what was the problem with the faulty ones and whether it has cleared. A situation awareness decision has to be taken to land at a suitable airport. When that can be done with the remaining ADR what is the purpose of applying a non standard procedure with unknown results? Especially after QZ8501. Only in a case where during application of memory items and while applying ADR check procedure before switching them off the ADRS recover it is possible to leave them on. If a good one was rejected by two bad ones in that case the control laws wouldn't have changed(because of single ADR fail) and with the recovery of the bad ones it should remain in normal law. Although I do not think the rejected one will come back.

Microburst2002
26th Aug 2015, 12:41
It is NOT a bad idea to switch ON an ADR that has been switched OFF previously by an ECAM line.

It IS a bad idea, though, to switch ADRs OFF or ON without first performing an ADR check procedure as per the QRH, since now we know that two rogue ADRs can vote a good ADR out, typically in icing conditions.

We should always suspect of any ADR FAULT. You can do the ECAM, but if later on you realized that the ADR is good and the others are bad (after the ADR CHECK PROC) then you must switch it back to ON, and the others OFF. As per the procedure.

It is not recommended to troubleshoot ADR issues without doing the ADR CHECK PROC. You might get in very serious trouble.

grrowler
28th Aug 2015, 04:28
We all agree that it's not a good idea generally to turn on a potentially faulty ADR, and once off, it's not possible to know for sure if the fault is gone. However that isn't really my question.

If you've got yourself all sorted on one ADR, and you're hand flying along miles from anywhere, I could imagine you might say "Well Shaggs, I reckon there's a pretty high chance that blockage was transient, let's see if we can get some things back. I'll keep flying if you try turning one on, be ready to turn it off straight away if needed".

Assuming it turns out to be fine, at that point I'm unclear whether systems come back automatically, faults are latched, further resets (eg PRIMs) are required for system recovery or what. The manuals seem vague on this (perhaps intentionally - onus on the pilots?).

Meikleour
28th Aug 2015, 09:26
Growler: I think you will find that the fault is "latched" for the rest of the flight.
I experienced a Dual ADR disagree in flight on a A330 in 1995 which was caused by transient icing of one pitot combined with a faulty ADR. The aircraft defaulted to ALT LAW and remained in such even after descent out of icing conditions and return of normal airspeed indications after some minutes.
Of course, as ever, Airbus may have since changed the software. I believe an increased time delay was introduced before "latching".

vilas
28th Aug 2015, 12:19
growler: From A330/340 FCTM AO-034 P 3/12
This should answer your question. You risk it without any gain.


TWO ADR OUTPUTS ARE ERRONEOUS, BUT DIFFERENT, AND THE REMAINING ADR IS CORRECT, OR IF ALL THREE ADRS ARE ERRONEOUS, BUT DIFFERENT :


Both the AP and A/THR disconnect. If the disagree lasts for more than 10 s, the PRIMs trigger the NAV ADR DISAGREE“ ECAM caution.
The flight controls revert to ALTN 2 law. The high speed protection and low speed protection are lost.
On both PFDs:


‐ The SPD LIM flag appears


‐ No VLS and no VSW is displayed


This situation is latched for the remainder of the flight, until the PRIMs are reset on ground, without any hydraulic pressure.
However, if the anomaly is only transient, the AP and the A/THR can be re-engaged when the disagree disappears.

ACMS
28th Aug 2015, 13:26
Oh come on Vilas I posted that exact info already in post number 3 above mate.....:D

Open Eyes and look up a bit.:ok:

vilas
28th Aug 2015, 13:53
ACMS
My apology. The thread is going in a circle so forgot to read all over again.

ACMS
30th Aug 2015, 04:36
:ok:

No worries.