In Alternate Law, AOA protection reverts to an airspeed basis (instead of the angle of attack sensor) so that is why loss of reliable airspeed indications causes loss of AOA protection.
I have watched this discussion for some time, and feel that possibly everyone should start singing from the same song sheet.
In the case of the quote above, the reason
Machinbird gives is clearly recorded in the BEA Interim Report No.1 -
Code:
o FLAG ON CAPT PFD SPD LIM and FLAG ON F/O PFD SPD LIM (2 h 10)
Symptoms: Disappearance of the display of the characteristic speeds
(in particular VLS and green dot) on the Captain and First Officer
PFDs, with display of the SPD LIM flag at the bottom of the speed
scales.
Meaning: This message indicates the unavailability of the FMGEC’s
characteristic speed calculation function.
- i.e. "
the FMGEC's speed calculation function is U/S"
I agree with
BOAC on this one. All that is required is a separate AOA indicator - nothing more, and with some basic numbers displayed to allow the PF to establish stable flight using attitude, power and AOA.
The Pitots have been blamed (at this stage) for causing the problems mentioned above, but no one knows whether the static ports were also involved, and if so what barometric functions also became suspect.
mm43