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A320 All ADRs Are Wrong during unreliable speed

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A320 All ADRs Are Wrong during unreliable speed

Old 7th Apr 2017, 14:58
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A320 All ADRs Are Wrong during unreliable speed

During Un.Speed ADR Cx Proc you aware that your all adr are wrong
You have to turn 2 of them off (IF THERE IS NO BUSS)
My question is which one should remain?
As I know,
If you keep ADR1 you can maintain XPDR/ATC1 and GPWS
If you keep ADR2 you can maintain XPDR2 and NW/STR
If you keep ADR3 you can use you LDG GEAR otherwise GRAVITY

I will be glad if someone lead me.Safe flights.
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Old 7th Apr 2017, 18:59
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Depends on your situation. Odds are, if you lost all three ADRs, it's already been a pretty bad day.


Is terrain an issue? If yes, might be a good idea to keep ADR1.


Gravity extension is not that big a deal. Neither is loss of NW steering necessarily an issue unless you're dealing with contaminated runways, so it's a judgment call.
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Old 8th Apr 2017, 07:42
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Why are you switching off the ADRs? If it is because they are faulty then they are faulty for everything they do. Period.
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Old 8th Apr 2017, 09:14
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How do you know that all (any) ADRs are 'wrong'?
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Old 8th Apr 2017, 09:14
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Originally Posted by vilas View Post
Why are you switching off the ADRs?
Because UNRELIABLE SPEED INDICATION PRO-ABN-34 tells you to do that.
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Old 8th Apr 2017, 09:16
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Originally Posted by PEI_3721 View Post
How do you know that all (any) ADRs are 'wrong'?
The procedure to switch 2 off is not only when they are all 'wrong', but also when the affected ADR(s) cannot be identified.
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Old 8th Apr 2017, 09:21
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How do you know that all (any) ADRs are 'wrong'?

reptile, my repost:
How do you know that the speed is unreliable?
Comparator alert; ADR fault but display remains visible - then how is a failure deduced?

What might cause speed to be 'unreliable'; what does 'unreliable' actually imply?
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Old 8th Apr 2017, 09:35
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The ADRs are able to detect most faults. In a case like that, the ELAC and FAC and/or FMGC will eliminate the erroneous ADR. The only effect of that would be that one display may be wrong, and autoland is downgraded CAT 3 SINGLE.

When all three are erroneous, and in some cases when two are off, the system may not be able to identify the the ADR(s) that are u/s. On both PDF's a SPEED LIM flag will appear. The ELACS will also trigger a NAV ADR DISAGREE caution.
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Old 8th Apr 2017, 11:31
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The OP has stated that he has concluded that all ADRs faulty. He hasn't asked how to detect it. He just wants to know which one to switch off. My answer was once it is determined all are unreliable it doesn't matter which two you switch off. Because you keep one ADR on for stall warning only which comes from AOA probe and is the only thing valid. All other function from faulty ADRS are equally unreliable.
Also it is not necessary that ADRs will detect faults and give you specific warning. Then AF447 wouldn't have been such a disaster. You may simply have speed increase one side and decrease on other side even the AP and ATHR may not trip. A 320 captain has given his nightmare in the SIM with this problem where he badly stalled and lost significant height but still didn't realise it was unreliable air speed. you will do well to read that. This topic is discussed many times on the forum so no need to waste time.
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Old 8th Apr 2017, 12:40
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Thanks reptile,
vilas, a critical aspect of such a scenario is how a failure could occur and then how the crew might detect it.
After identification the aircraft procedures can be followed with appropriate consideration of which system aspects remain and / or are required.
If this type of failure is extremely remote then the value in training might be limited, further still its pointless to read a checklist if the failure has been 'announced' - expected.
The training value in extreme situations is the detection and understanding of the failure and the flight condition, these should lead to the correct checklist. (AF447 followed an inappropriate part of the checklist - failed to understand the situation. What was trained / refreshed to meet the updated regulatory requirement. Who checked if this was done / understood.)
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Old 8th Apr 2017, 13:06
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@vilas

Valid point - I've misunderstood your first reply
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Old 8th Apr 2017, 18:39
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I'm sure this will turn out to be a stupid SLF question, but it seems like a wholly unreliable ADR controlling the nose wheel steering or the landing gear couldn't be a good thing (at least if might mean uncommanded steering inputs or gear retraction). Is there a way to isolate those functions if you leave the associated ADR on for stall warning purposes? (Of course, if those functions are just controlled by the same CB as the associated ADR, uncommanded operation wouldn't be a concern. But then which CB you pulled would determine which functions you lost.)
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Old 9th Apr 2017, 01:25
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Chu Chu, what you are missing is the "fail-safe" philosophy. It is integral to the design of aircraft systems and a requirement for certification.

Simply meaning that if anything breaks / faults, the resulting state may be a limited functionality, but strictly not that of an unpredictable behaviour. The failure modes (cases) are thorougly investigated at the design stage.

For instance the nose wheel steering above. Normally it blends inputs from rudder pedals and the two dedicated tillers to command nose-wheel deflections. The ratio is dependent on airspeed. If the speed measurment is suspect or wrong - by design then - the value of speed will be disregarded up to the point when nose-wheel steering is made unavailable. (there is some dampened free-castor, so afterwards you still can maintain some directional authority through assymetrical braking). True, when the system is unable to self-diagnose the errorneous reading, you may need to turn the Air Data System unit off, that is all to it.
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Old 9th Apr 2017, 17:22
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FlightDetent,

Thanks for the careful and patient explanation. At the risk of further trying everyone's patience, it seems as if the reason to shut down 2 ADRs would be that the fail-safe philosophy didn't work as well as expected in practice. If ADR 3 might have an unreliability the system hasn't detected (which I think is what we're assuming), and you left it on, it seems like you could still end up with something like a large NWS deflection early in a cross-wind landing (because the ADR thought the airspeed was low when it wasn't).

Or maybe the answer is that the NWS reverts to fail-safe mode at the first hint of trouble with the ADRs, so it doesn't matter what you shut down? Or perhaps there's something else, maybe a ground-speed input, that would prevent the NWS from doing anything too unexpected (in which case possibly keeping NWS might be a reason to keep ADR 3 on)?
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Old 23rd Apr 2017, 12:25
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I want to switch at least two ADR because otherwise protections can take the controls.Like V alpha prot
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Old 24th Apr 2017, 15:58
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Topla
Unreliable speed has nothing to do with AOA probes so alpha prot is not the issue. It's Pitot/static isse. You switch off two ADRs because two rogues shouldn't kick out the third good guy.
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Old 24th Apr 2017, 17:38
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When aircraft uncontrollably dives or pitches up because of the protection, the last thing you need to do is to spend few seconds thinking which ADRs to switch off. Every extra second could be deadly on top of your already significant stress. Just switch ANY two of them off as Airbus recommends. And this should be a memory item, BTW.
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Old 24th Apr 2017, 18:16
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I sometimes think we take things too far with abnormals.

3 ADRs? Fat chance. I lost an ADR over the Atlantic once. Once.

Relax and let the Magic Electric Jet get you there in peace.
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Old 24th Apr 2017, 18:32
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The OP is not talking about 3 ADRs failing which is highly unlikely, they are talking about the inputs to all 3 ADRs being unreliable or being unable to identify which one or two is still reliable which is entirely possible. Airbus doesn't specify which one to leave on so take your pick, leaving No. 3 on would avoid being distracted by potentially unreliable data on the two PFDs.

Hopefully if and when it happens you will be flying an aircraft with the GPS back up speed scale which simplifies the task hugely.

Last edited by Max Angle; 24th Apr 2017 at 18:47.
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Old 24th Apr 2017, 20:33
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Originally Posted by Chu Chu View Post
If ADR 3 might have an unreliability the system hasn't detected (which I think is what we're assuming), and you left it on, it seems like you could still end up with something like a large NWS deflection early in a cross-wind landing (because the ADR thought the airspeed was low when it wasn't).
I would expect the design engineers to identify such scenario and use yet another level of logic to avoid the trap. Which is it, if any in this particular scenario - I am not educated to even make a guess.
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