Unreliable Speed A320
Thread Starter
Joined: Dec 2008
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From: Birmingham
Unreliable Speed A320
Hello friends,
quick one on this. We had the scenario in January which was: ADR 1 totally inop, ADR 2 speed unreliable and altitude ok, ADR3 inop. So the checklist asks for identifying the affected ADR. Ok, all three are actually unreliable. BUT ADR2 has a valid Altitude which can be used and makes it much easier. So why does Airbus say you have to switch it of? Because of the warnings related to the unreliable speed on adr2? Otherwise you could keep it running?
Thanks so much
SW
quick one on this. We had the scenario in January which was: ADR 1 totally inop, ADR 2 speed unreliable and altitude ok, ADR3 inop. So the checklist asks for identifying the affected ADR. Ok, all three are actually unreliable. BUT ADR2 has a valid Altitude which can be used and makes it much easier. So why does Airbus say you have to switch it of? Because of the warnings related to the unreliable speed on adr2? Otherwise you could keep it running?
Thanks so much
SW
Joined: Jun 2009
Posts: 87
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From: Mars
Depending on aircraft capabilities (BUSS, DBUS), there are some differences. But typically you keep one Adr on to prevent flight control laws from using the bad ADR data, in which case you can keep ADR 2 on and then off 1 & 3. On aircraft with the BUSS you turn off all ADRs below FL250 and the altitude is replaced by the GPS altitude.
Joined: Jun 2007
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From: Wanderlust
Hello friends,
quick one on this. We had the scenario in January which was: ADR 1 totally inop, ADR 2 speed unreliable and altitude ok, ADR3 inop. So the checklist asks for identifying the affected ADR. Ok, all three are actually unreliable. BUT ADR2 has a valid Altitude which can be used and makes it much easier. So why does Airbus say you have to switch it of? Because of the warnings related to the unreliable speed on adr2? Otherwise you could keep it running?
Thanks so much
SW
quick one on this. We had the scenario in January which was: ADR 1 totally inop, ADR 2 speed unreliable and altitude ok, ADR3 inop. So the checklist asks for identifying the affected ADR. Ok, all three are actually unreliable. BUT ADR2 has a valid Altitude which can be used and makes it much easier. So why does Airbus say you have to switch it of? Because of the warnings related to the unreliable speed on adr2? Otherwise you could keep it running?
Thanks so much
SW
Joined: Jun 2007
Posts: 3,443
Likes: 39
From: Wanderlust
Joined: Jun 2007
Posts: 3,443
Likes: 39
From: Wanderlust
You needed to provide following information in the original question:Whether aircraft had GPS?Whether aircraft had no BUSS, old BUSS or the new BUSS?since you have GPS but no BUSS you may keep the ADR2 but considering the complexity of the failure possibility of altitude becoming erroneous cannot be ruled out and CM1 doesn't have altitude on PFD anyway. So it's better to use GPS altitude from MCDU GPS page to fly the approach.
Joined: Jun 2007
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From: Wanderlust
Airbus should know better. They display GPS altitude on the BUSS. So can't be that bad. Better than depressurize and freeze passengers. Unreliable speed is bad as it is managing a descent to preserve passenger's eardrums, well! Possible in the sim may be.
Joined: Jan 2014
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From: N5109.2W10.5
ATC radar cannot measure aircraft Altitude independently - they can only report the transponder altitude data transmitted from the aircraft - which will always agree with one of the onboard altimeters.
So there is no X-check there.
Joined: Jun 2007
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From: Wanderlust
Yes! There was a fatal accident due to radar altitude.
Joined: Jan 2014
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From: N5109.2W10.5
I bet you’re thinking of Aeroperu Flight 603
”The pilots incorrectly believed that they could figure out the actual aircraft altitude by asking the controller, but neither the pilots nor the controller realized that the altitude information displayed on the controller's screen was sent from the aircraft's Mode C Transponder. As the transponder was receiving the same erroneous altitude information being displayed on the aircraft's altimeter, the altitude on the controller's display was also incorrect.”
”The pilots incorrectly believed that they could figure out the actual aircraft altitude by asking the controller, but neither the pilots nor the controller realized that the altitude information displayed on the controller's screen was sent from the aircraft's Mode C Transponder. As the transponder was receiving the same erroneous altitude information being displayed on the aircraft's altimeter, the altitude on the controller's display was also incorrect.”
Last edited by Goldenrivett; 10th April 2023 at 21:31. Reason: Typo
Joined: Aug 2007
Posts: 98
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From: Middle East
You needed to provide following information in the original question:Whether aircraft had GPS?Whether aircraft had no BUSS, old BUSS or the new BUSS?since you have GPS but no BUSS you may keep the ADR2 but considering the complexity of the failure possibility of altitude becoming erroneous cannot be ruled out and CM1 doesn't have altitude on PFD anyway. So it's better to use GPS altitude from MCDU GPS page to fly the approach.
Old BUSS /New BUSS !!!!!
Can u pls elaborate
Joined: Jun 2007
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From: Wanderlust
Airbuses come in four types.
1. Without Back Up Speed Scale.
2. With irreversible Back Up Speed Scale
3. With reversible Back Up Speed Scale.
4. With Digital Back Up Speed where alternate actual calculated speed replaces pitot static speed.
1. Without Back Up Speed Scale.
2. With irreversible Back Up Speed Scale
3. With reversible Back Up Speed Scale.
4. With Digital Back Up Speed where alternate actual calculated speed replaces pitot static speed.
Last edited by vilas; 11th April 2023 at 18:06.
Joined: Sep 2011
Posts: 350
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From: FL390
The problem with this is that all you know is that at that particular moment in time you have an altimeter that agrees with GPS altitude. Air data problems can be quite insidious in that a faulty system can provide seemingly accurate data at one moment in time, at a specific speed and altitude. This is why Airbus recommends that you switch off all three and rely on the BUSS if fitted.
Joined: Jun 2007
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From: Wanderlust
Last edited by vilas; 12th April 2023 at 05:42.
Joined: Apr 2023
Posts: 69
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From: Mumbai
The problem with this is that all you know is that at that particular moment in time you have an altimeter that agrees with GPS altitude. Air data problems can be quite insidious in that a faulty system can provide seemingly accurate data at one moment in time, at a specific speed and altitude. This is why Airbus recommends that you switch off all three and rely on the BUSS if fitted.
