Below are the IAS approximations taken from groundspeed readouts from FR24 for the flight. They were taken as a TAS and converted to an CAS, therefore they are not corrected for wind effect. There was a southerly blowing at around 13 knots in the lower levels, rising to about 30 knots in the higher levels.
I don't know how closely these correspond to the actual IAS considering all the possible errors and the fact that the aircraft was descending rapidly, however...
VMO/MMO for the A320 are 350 knots/0.82
32625 CAS 296 EAS 279 MN .823
28875 CAS 313 EAS 297 MN .805
24650 CAS 343 EAS 328 MN .81
20300 CAS 358 EAS 345
17000 CAS 355 EAS 345
15000 CAS 355 EAS 346
13300 CAS 358 EAS 351
11125 CAS 355 EAS 349
9975 CAS 350 EAS 345
8259 CAS 342 EAS 339
6925 CAS 343 EAS 340
There remains the strong possiblity that the hi speed protections activated during the descent. They activate @VMO +6
Normal Law - High Speed Protection
When high speed protection is active:
The autopilot disconnects
High speed aural warning is heard
Automatic pitch trimming stops
Bank angle limit is reduced from 67° to 45°
Positive spiral static stability is introduced to 0° bank angle (instead of 33° bank angle in normal law), so that when the side stick is release it always returns to 0° bank angle instead of 33° bank angle
High speed protection can be overridden, but side stick nose-down authority is reduced and a positive pitch-up command is introduced
If the stick is released, the airplane continues to pitch-up until the airspeed slows to VMO/MMO at which point the high speed protection is deactivated and normal control laws are restored.
The questions are whether this aircraft went fast enough to activate the high speed protections? If it did, why didn't it pitch up, and what was it doing flying so fast in the first place?
If pilot incapacitation occurred, why did the Auto-pilot maintain maximum possible speed, and why did it not capture an altitude selected on the FCU?
The standard drill for an emergency descent involves keeping the autopilot engaged if possible, dialing a lower FCU altitude, turning off the airway and commencing the descent by selecting Open Des.
The aircraft continued on track but commenced descending at maximum speed, so none of that appears to have been done. Unless there was a massive un-correctable error in the Auto-flight system, there had to be pilot intervention to get it to do that.
This is a very strange accident.