Dozy wrote in post 67:
@CONF - I'm not in denial - the alpha protections follow pilot input up until the point safety boundaries are reached and will maintain that, in much the same manner as the T7 will progressively counter input through the force-feedback. Of course, as the Mach number increases, the pitch down will also increase, but it's not going to suddenly force the aircraft into a significant dive, in fact it won't descend at all if corrective action is taken.
Well dozy, you are wrong. Some information regarding the incident from my company:
In the recent event, all three probes became frozen and the aircraft erroneously detected an ‘incorrect angle of attack’ scenario which triggers Alpha Prot. As the AOA probes are frozen Alpha Floor will not be activated as the triggering AOA limit is not reached . As designed, the aircraft protection activated and a nose down input was introduced. Unfortunately, as the probes were frozen (and continually sensing the incorrect alpha), the AOA did not reduce and the flight controls continued to demand a pitch nose down. Within 10 seconds, the aircraft had achieved 12 degrees nose down pitch and a rate of descent of 9400 fpm.
Aft sidestick input had no effect and the aircraft continued to pitch nose down.
Turns out it WILL put the aircraft in a sudden and significant dive that will only become worse. 10 seconds is about 1600ft at that rate, a dive!!!
Turning off 3 ADR's might have saved them but it could have made their day significantly worse:
Back Up Speed Scale (BUSS), which is fitted onto newer aircraft relies upon AoA inputs. It must not be used, so DO NOT switch off more than 2 ADR’s.