Lonewolf 50, Continuing on the "gyro re-alignment" subtopic:
I'd guess that a checklist or something like an ECAMS resource in the cockpit would walk the pilots through the step by step if such a realighment/recaging were necessary inflight.
Perhaps not, perhaps fixed only on the ground.
As far as I understand, such manual operations should not be necessary.
I did some googling and found out about this
Northrop Grumman LTN-101/101E GNADIRU (Global Navigation Air Data Inertial Reference Unit) which is certified for Airbus [correction: but was not installed on AF447 which had Honeywell units, see next post below].
As the description says, it integrates air data, inertial (solid state gyro based) and GPS data and continuously "realigns" or calibrates itself to maintain data integrity using something the manufacturer calls
AIME (Autonomous Integrity Monitored Extrapolation) technology. "AIME continuously analyzes available satellite and inertial signals. If the data’s integrity is compromised, AIME automatically uses the aircraft's position history to maintain accuracy and integrity. Onboard predictive Receiver Autonomous Integrity Monitoring (RAIM) programs are not required".
This is probably a similar (but enhanced) concept to that used in many car navigation systems, which use GPS for primary positioning but revert to inertial sensors (solid state MEMS) when GPS signal is lost in a tunnel.
An interesting "side feature" of such an integrated system is that you could use it "in reverse" to calculate e.g. the strength and direction of the wind gusts that hit the airplane, by comparing the differences between air data, inertial and GPS data. It will be interesting to see if this kind of results will appear in BEA's report, given the turbulent weather conditions that we know were in the vicinity of AF447.