Originally Posted by
hambleoldboy
I would think that the FPV symbols are generated by the IRU's therefore unaffected by unreliable air data inputs...?
Well... Yes... and no. As per BEA's #2 interim report (bold is mine):
ACARS Messages:
02:11:00 - .1/WRN/WN0906010210 228300106FLAG ON CAPT PFD FD
02:11:15 - .1/WRN/WN0906010210 228301106FLAG ON F/O PFD FD
Symptoms:
Disappearance of the FPV (bird) on the PFDs, Captain and First Officer sides, and display of the corresponding flag.
Meaning:
This message indicates that the flight path vector (FPV) function is selected but unavailable. In order to lose completely this function, which is elaborated by the three IRs, in a way that is compatible with the CFR, one of the following three conditions must be met for each ADR:
- barometric vertical speed higher, as an absolute value, than 20,000 ft/min,
- true air speed higher than 599 kt,
- measured calibrated airspeed lower than 60 kt.
Once the operating conditions are satisfied again, the FPVs reappear on the PFD (if TRK/FPA mode is still selected).