HN39;
A misunderstanding of the sign of the pressure differential created the "error" in the Squair calculations! So the rational behind his argument fails.
However, the damage reported and the BEA's determination of how the flight ended do not match the implied vertical speed. A closer look at when the CVS advisory may have been initiated, and some juggling of a flight termination time could give a v/s that fits with the BEA reports (high vertical speed, 'en ligne de vol', and 'arm 36 g' etc..).
So, here is another look at what may have happened:-
Two independent pneumatic safety valves prevent the cabin pressure from going too high (8.85 psi above the external ambient pressure) or too low (- 1 psi below ambient pressure).
* hcbn = 7350 – 750 ft/min x 251/60 = 7350 ft - 3138 ft = 4212 ft
Now as a 2.03625437 inHg pressure change gives approximately a 2036 ft altitude change, and as the external pressure is 1 psi more than the cabin pressure (3), the external or aircraft altitude (hacft) is simply:
* hacft ? 4212 - 2036 ft = 2176 ft
2:14:15 - 2:14:29 = 14 sec > rate of descent = 9326 fpm *matches BEA summary of crash.
2:14:21 - 2:14:29 = 8 sec > rate of descent = 16320 fpm *excessive
The 9326 fpm rate uses the earliest time the Cabin Vertical Speed advisory could have originated, i.e. immediately following commencing transmission of the preceding fault report message with time of receipt 2:14:20. A further assumption is that the flight terminated 1 second after the Cabin Vertical Speed warning receipt confirmation by the aircraft [02:14:28].
NOTE: WRN messages take precedence over FLR messages.
2:14:20 FLR/FR0906010213 22833406AFS 1,,,,,,,FMGEC1(1CA1),INTERMITTENT
2:14:26 WRN/WN0906010214 213100206ADVISORY CABIN VERTICAL SPEED
Therefore, a vertical speed in the order of 9,000 fpm looks like a possibility with a crash time close to 02:14:30. I know this has been raised before, but with
Svarin raising the issue, another look was worthwhile. In fact, I believe
Machinbird offered a similar v/s some time ago.
mm43