Finn47 asked;
"Plunging 8000 feet in ten seconds", passenger says. Is that credible?
When an airliner is cruising normally at say 37,000ft there is, in normal weather conditions, a sensible and safe margin between the aircraft's stall speed and it's critical mach number. It is theoretically possible that a sudden encounter with a jet stream when cruising at high altitude could cause a sudden and significant change in indicated airspeed resulting in either a stall or mach tuck. The higher an aircraft flies, the closer the stall speed gets to the critical mach number and the less safety margin an aircraft has between these limits. An extreme example of this was the U2 which would fly within 5kts of stall speed and 5 kts of the critical mach number when cruising at 70,000ft. It's said that if a U2 performed a tight turn at that altitude it could cause one wing to stall and the other to exceed the critical mach number.
Stalling or mach tuck at cruise altitude caused by a sudden and significant change in wind strength / direction could result in a departure from controlled flight and could cause a significant loss of altitude. I'm not suggesting that this is necessarily what happened to the Qantas A333, just pointing out some basic aerodynamic principles.
Does anyone know what altitude the A333 was cruising at and what the margin between stall speed and critical mach number would be at that altitude?
More info here;
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