Hi Bearfoil,
Originally Posted by Bearfoil
You mention that BEA do not state any "recognition" (by pilots) of noticeable a/s problems prior to a/p loss. You also mention that many prior cases of UAS did have such recognition by pilots. You call it 'brutal'. Can you explain?
In many UAS events, (but not all), the attention of pilots was at first attracted by either airspeed fluctuations on PFDs, either autothrust changes before autopilot disconnected. In one case, it is mentioned that CAS made several yo-yos on both PFDs. In those recorded cases with fluctuations, this NAV IAS DISCREPANCY message would tilt on ECAM. It means that airspeeds displayed on each PFDs are outside a certain range, which is constantly monitored by the system, while certified instrument possible variations at cruise, depending on source, altitude and speed are below Mach 0.009 (=3-4 kt above FL350).
In fact, I noticed an incoherence about this NAV_ADR_DISAGREE message: In the documentation, like
A33Zab mentioned it above, it is stated that in case of 2 or 3 ADR fault, this ECAM would be displayed, while I believe this is only true in the first case (2 ADRs) because it is contradictory with NAV_ADR_DISAGREE condition which needs first an ADR to be rejected by the PRIMs (this rejection of the "outlier" is discrete). Hence, in case of triple ADR fault happening in a very short time, without a single ADR drifting earlier from the other two, this condition won't be true.
Our case signature of this first ADR fault (0210) is a triple one. Beside, it is much more logical with the Probe-Pitot fault which is also a triple one, the system being unable to determine which one of the three has faulted. How could the system "eliminate" the first ADR by itself?
Hence, this is why I'm saying it was brutal as there was a fast ice build-up, a sharp speed drop, without erratic speed readings, affecting all the probes in few seconds that caught the crew by surprise. No warnings due to autothrottle behavior or IAS DISCREPANCY tilting on ECAM display.
But please, Bear, don't rebounce on my posting in order to advance your usual "structural" failures fantastic theories, as this was a genuine ADR fault due to severe probe icing in all certaincy.
Their huge problem was that when the first ADR fault self-cleared at 0211, a second followed at 0211:40 (invalid parameters), then possibly a third one at 0212 (ADR DISAGREE)...
Hi HN39,
Originally Posted by HazelNuts39
reference?
See the Expertise Judicial report link I posted few pages back. (here it is:
rapport d'expertise Rio-Paris)