Hi,
1. Why did the Pitots ice up?
Because the a/c flew into a region with certain characteristics, equipped with 3 identical Air Speed sensors (Pitot tubes) not adequate for this "region". These sensors (Thales) presented some anomalies before (in other flights) and were scheduled to be replaced by BF Goodrich ones. The accident occurred before the change in the F-GZCP plane.
2. Why did the A/P and A/T disconnect?
Because the Airbus SAS System requires reliable information from the sensors in order to work at full specifications. When entering (a region with certain characteristics) and the sensors start to present anomalies, the System change the a/c operation mode (LAW) disconnecting A/P and A/T, etc. We donīt yet have information on other (possibly) occurred sensor anomalies that could also lead to this "disconnection" (due mode change, LAW).
3. Why the zoom climb without clearance from ATC?
In this region they were capable to use HF and Data comm. They tried to use Data comm with DKR ACC for 3 times, some minutes before. During the sudden zoom climb they certainly were not able to even think on comm for FL change.
4. Why the sudden reduction of speed at top of climb?
The a/c changed speed by altitude and with THS "going" to 13° UP with/and NU commands, she eventually stalled. And they were facing non reliable air speed in their displays and also in the ISIS (3rd and redundant resource). So the real speed (during many moments) after icing up
nobody will ever know. Just estimate, based at other data, (risky estimate). The info was just lost (simply not measured, due "sub heated sensors"
).
5. Why when at the same time the plane went into the thunderstorm?
The decision making to go straight (and not deviate) was made before. "Inside" the WX they started a
12° LH deviation, then the zoom climb started. We donīt have the CVR info to understand on the "decision" to go in the straight route. Other planes deviated. On this particular aspect see BEA reports and
Tim Vasquez
below 60 kts, it is out of control!
Nobody has the "real" speeds during many moments during this phase. The sensors were just not working properly. The FDR will show us the moments when the speeds were correctly measured. (Again, the a/c was equipped with air speed sensors
not compatible to the region she entered)
The flight controls do not have ANY effect.
The
(very little) information BEA released on that suggest they had "some control".
Thunderstorms are known to contain strong up and down drafts. For 50 years we in the pilot community have been warned to avoid, avoid, avoid them.
Several cases of Unreliable Air Speed occurred during deviations from WX.
(*)
KISS principle - Wikipedia, the free encyclopedia
Why didn't they deviate?
CVR certainly will help us to understand why.