Will;
See "PRIM1" specifically. Inop or selected off, the chain is interesting relative to HS movement and the possibility of overspeed leading to upset.
Though some will know this, I think just to be absolutely clear for all, it is the elevator movement, not the "HS movement" which was commanded in the QANTAS upset. Although the horizontal stabilizer movement is controlled by PRIM1, it is a trim function not a flight control function. It is possible that ND trim motion occurred but not only have we no evidence to believe that, but we do not have evidence of a high-forward-speed, high-rate-of-descent impact with the sea, which an uncontained/uncorrected ND HS trim condition would almost certainly cause. (Note: HS trim does have manual reversion backup).
augustusjeremy;
Just so all are clear on IRS alignment procedures, an IRS cannot be aligned when in motion. Its alignment process uses the angular acceleration sensed by the laser gyros and a mathematical Euler pendulum (theoretical center of the earth perpendicular to the aircraft attitude at rest, if I recall - someone can correct me here, it's been a while), to "null" the only acceleration affecting attitude. The accelerations are "resolved" to a position from which the IRU calculates latitude.
I'm only trying to convey a sense of the alignment process and not a blow-by-blow detailed description, (unnecessary), and why alignment can't be done if the aircraft is at all in motion. There is no such thing as "entering one's position" or taking present positions from the other IRSs - the potential for gross errors are obvious. In fact, a good stiff breeze pushing the tail around while the aircraft is parked at the ramp will upset or delay the alignment process as will an inadvertent towing of the aircraft from one gate to another, (it's been done...!). Forgive me for droning on, but I think this technical aspectd needs to be clear.