Cabin Vertical Speed Advisory - revisited
Thanks to ACARS being free to transmit the CVS advisory in real-time, here is what actually 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) or 7350 ft - 3138 ft = 4212 ft
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, the external or aircraft altitude (hacft) is simply:
* hacft = 4212 - 2036 ft = 2176 ft
2:14:16 - 2:14:28 = 12 sec > rate of descent = (2176/12) x 60 = 10,880 ft/min.
BEA's Rate of Descent at impact = 10,912 ft/min.
The 10,880 ft/min rate uses the earliest time the Cabin Vertical Speed advisory could have originated, i.e. coincident with commencing transmission of the preceding fault report message [02:14:16] with time of receipt 2:14:20. A further assumption is that the flight terminated coincident with 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
The final satellite link with AF447 terminated a few milliseconds prior to the aircraft's impact.