Rejection of AOA Sensors by ELAC on A320
Hey guys,
does anybody know at how many degrees of difference one AOA Sensor is rejected/"voted out" by the ELACs? I had a rather big discrepancy between the FMGC weight and the FAC calculated weight recently (which also triggered the "Check GW" message) and resulted in a difference of around 10kts between the characteristic speeds on the PFD and the FMGC (Green dot etc). The load sheet was definitely correct and I have heard from other crews have experienced similar issues on this specific aircraft in the past, so I am suspecting some kind of AOA sensor (or possibly ADR/FAC) problem. The strange thing is that both PFD seemed to be affected in the same way. According to the Alpha Callup there was a difference of around 0.6 degrees between the AOA provided by FAC1 and the one provided by FAC2 (the difference in gross weight between FMGC1 and FAC1 was in excess of 7 tons, but this only became apparent after around 2 hours of cruise flight, the difference between FMGC2 und FAC2 was just under 7 tons, so the "Check GW" message was only triggered on the left MCDU). Does anybody have a plausible explanation for this behavior (except load sheet error which I would exclude as it apparently happened on different flights to other crews as well - we also double checked the load sheet after being the "Check GW" message to exclude a load sheet error)? It seems to be hardly conceivable that independent sensors fail in a very similar way over several flights (i.e. excluding issues like freezing water within probes etc.). Is there any way to access the AOA value from the STBY AOA trough the Alpha Callout menu?