Originally Posted by Max Angle
I have to say that in 7-8 years of flying the thing I have never once felt the need to dive into AIDS to find the "true" weight. I have long suspected that the information derived from the angle of attack vanes is just as prone to error as those derived from loadsheet weights, a tiny error in the measured AOA has the potential to generate quite a large discrepancy in sensed weight I would have thought.
Yes. Alpha probe errors can be significant- 0.1 degree equals a three ton, 4kt error. But the voter function between the three alpha values offers system protection against gross errors.
Airbus states the errors of the FMGC speeds equals +/- 2kts and +/- 3 kts for the FAC generated speeds.
The threats as I see it are 1) pilots flying at VLS when FMGC speeds are incorrect. This is a product of a poor loading procedures- inaccurate nominal weights and incorrect load sheets. This is airline dependant. I worked for an airline where loaders took bribes and 4 tonnes overweight normal. I have also worked for an airline where similar errors occur due conservative nominal weights. The major risks in this scenario are tailstrike susceptability and hard landings.
2) Charateristic speeds being too close to VFE. When G dot equals VFE Flaps one, forewarning to slowdown early in difficult conditions useful to avoid overspeeds and unneccessary go arounds.
Checkings FAC weights through AIDS is very useful in the above cases- and good practice with some airlines depending on operational circumstances.