Hi A33Zab,
Originally Posted by A33Zab
for this failure message, in fact you should read: PROBE-PITOT 1+2 or 2+3 or 1+3 (9DA?). Meaning there are 2 or more PITOT-PROBES affected but BITE/CMC can't determine which 2 (or more) are faulted.
Which is also exactly my reading of the fault:
total pressure was out of boundaries [meaning that ADRs polled airspeed value dropped by 30 kts in one second or less] but was different at each probe-pitot source (9DA1, 9DA2, 9DA3)
Then, your explanation is the same than mine : the system can't dertermine which source (pitot-probe) faulted, because all 3 values were at first valid and coherent (condition for triggering this fault and monitoring), then diverged without remaining consistant with each others, hence, there was NOT an ADR DISAGREE message that could be triggered at this point (0210:05). The system was not able to eliminate the outlier ADR during the speed monitoring sequence (DISAGREE condition false: elimination of 1 ADR and other two ADR imputs different). Consequently, all three ADR output would be rejected both at PRIMs (FCPC1 & 2) and AFS level (no matter if one ADR output could have been valid).
Also IAS DISCREPANCY would be triggered if PFD 1 & 2 readings were showing a difference of at least 16 kt during some time. This condition may not have lasted long enough for doing so, hence no ACARS if such fault would be sent (not sure) after consolidation (2-3 seconds). It doesn't mean that this ECAM wasn't displayed at all in the cockpit, but it could have been intermitent during a very short duration. Also, there is nothing in BEA narrative telling us that the crew noticed something before AP disconnected. In many other cases, crews were alerted by experiencing airspeed fluctuations; it seems not to be the case here: it was brutal.
Consequently from those conditions, I'm deducing that ADR2 was also faulty and could have been the very first to drop. This is fully coherent with an environmental fault affecting the same probes, the same way, in a very short time interval.
Originally Posted by A33Zab
The first UAS was only transient, ADR 1 lasted only few seconds, ISIS (ADR 3) was absent for nearly 1 minute.
Your conclusion doesn't match with the data:
In BEA last note :
1)
The recorded parameters show a sharp fall from about 275 kt to 60 kt in the speed displayed on the left primary flight display (PFD), then a few moments later in the speed displayed on the integrated standby instrument system (ISIS).
2)
The inconsistency between the speeds displayed on the left side [ADR1]
and on the ISIS [ADR3]
lasted a little less than one minute [inconsistency stopped before 0211:05]
From the BEA narrative:
- 0210:05 -> ADR1 followed by ADR3 sharp fall;
- 0211:06 -> ADR1 & ADR3 speeds coherent and "valid" again => 1 minute error;
- 0211:40+ few seconds ->
all of the recorded speeds became invalid again (1). Note 1: When the measured speeds are below 60 kt, the measured angle of attack values are considered invalid and are not taken into account by the systems. When they are below 30 kt, the speed values themselves are considered invalid.
Consequently, the ADR DISAGREE message triggered (0212 => 0211:40+) is due to this second (or later) speed/alpha issues with ADRs, at which time conditions were different as 1 ADR would have been rejected at FCPCs level.
Your above conclusion doesn't match also with the first BEA report (see p.54-55) about this fault explanation:
"The presence of the F/CTL RUD TRV LIM FAULT message indicates that EFCS monitoring had been activated and that the alternate law had been maintained."
Hence, it was already obvious from all the systems declared INOP that the first probe fault was NOT
transient and it was confirmed by the DFDR showing that the inconsistency lasted about 1 minute on both ADR1 & ADR3 (more than enough for a triple ADR fault condition).
You should also keep in mind that this sequence is not from a PFR (Post Flight Report) but a CFR/ACARS, hence, everything is not sent by this mean (e.g. no cockpit Stall, overspeed warnings). Failures are labelled following their logical compilation order and could have covered various system messages having the same ATA header => 341.
You may want to list every ATA 341 fault at FCPC and AFS level and see what they could have been during this 1 mn correlation window opened.
Also, AIRBUS acknowledged this PROBE-PITOT fault as being possibly part of an UAS signature, even if not the more frequent:
Originally Posted by AIRBUS
TELEX - OPERATORS INFORMATION TELEX
TO: A330/A340/A340-500/A340-600 Operators
SUBJECT: ATA 34 - REQUEST FOR INFORMATION CONCERNING IN-FLIGHT UNRELIABLE AIRSPEED
OUR REF: SE 999.0049/09/VHR dated 09 JUN 2009
[...]
2/ TYPICAL SIGNATURE OF UNRELIABLE AIRSPEED
To be sure that Unreliable airspeed events are correctly identified, please report events corresponding to the criteria as follows:
- Crew report indicates loss or discrepant IAS (Indicated Airspeed) on CAPT and/or F/O PFD and/or Standby Airspeed indicator (ISIS).
- Typical ECAM Warnings were seen:
NAV ADR DISAGREE
NAV IAS DISCREPANCY
F/CTL ALTN LAW
F/CTL RUD TRV LIM 1(2) FAULT
AUTO FLT AP OFF
AUTO FLT A/THR OFF
STALL WARNING (audio call-out)
AUTO FLT REAC W/S DET FAULT
- Fault Message "PROBE-PITOT 1+2/2+3/1+3" was possibly also seen.
- Maintenance report indicates that event was NOT due to a system failure.
The TBS (see below) mention about this fault "Disagree of the Pitot Probe Data in the FCPCs" that if the fault was transient, F/CTL ALTN LAW, would have been displayed only few seconds in the cockpit (then return to NORMAL, while an acknowledgement from the crew is also stamped 0210:16)- Beside, there would be no subsequent ECAM warnings and flags on PFDs.
Originally Posted by TBS
34-11-15 EFCS2 :
TASK 27-91-00-810-822
Disagree of the Pitot Probe Data in the FCPCs
1. Possible Causes
...pitot probe
2. Job Set-up Information
...A. Referenced Information
.........AMM 34-11-15-000-801 Removal of the Pitot Probe (9DA1, 9DA2, 9DA3)
.........AMM 34-11-15-200-801 Inspection/Check of the Pitot Probe (9DA1, 9DA2, 9DA3)
.........AMM 34-11-15-400-801 Installation of the Pitot Probe (9DA1, 9DA2, 9DA3)
3. Fault Confirmation
...A. Test
........(1)Not applicable, you cannot confirm this fault on the ground.
4. Fault Isolation
...A. If the crew made a report that the F/CTL ALTN LAW or F/CTL DIRECT LAW warning was shown on the EWD for some seconds only:
.........- no trouble shooting is necessary.
...B. If the F/CTL ALTN LAW or F/CTL DIRECT LAW warning is shown and stays on during the flight:
.........(1)Do the inspection of the pitot probe (9DA1, 9DA2, 9DA3)
.........AMM TASK 34-11-15-200-801
.........replace the defective pitot probe (9DA1 or 9DA2 or 9DA3)
.........AMM TASK 34-11-15-000-801 and AMM TASK 34-11-15-400-801