Possible implications of CABIN VERTICAL SPEED ADVISORY (cont’d)
Thanks for the Pressurisation schematic, mm43. It shows that static (external) pressure is obtained via the Air Data elements of the ADIRUs, as expected (originating from the static ports). Unfortunately, it doesn’t show where within the pressure hull the cabin (internal) pressure signals come from. I think we can assume that any external probes are not involved? If so, any available Cabin VS data (and here we have one) are likely to be uncorrupted by issues such as external icing or excessive flight parameters.
By the way, I think the Safety Valve on the rear pressure bulkhead only opens to relieve grossly excessive differential pressure, not for inward relief.
Am I correct in inferring that the ECAM message could be triggered by either a negative or a positive VS exceeding 1800 ft/min, lasting at least 5 seconds? If so, a double engine flameout might result in a temporary positive (climb) VS of this nature, before the outflow valve had time to close. Once the Outflow Valves had shut, the cabin VS would fall well below 1800 ft/min. System design would not allow a simultaneous loss of both AC (engine) generators to disable both Outflow Valves in an open position. But power to the valve motors might be interrupted temporarily.
I may be revisiting ground discussed previously, but − when considering the possibilities − could we add the above scenario to the more likely one in which the aircraft has descended rapidly to the cabin altitude, and then takes the cabin with it? Has a double engine flameout at high altitude already been ruled out?
Chris