A320 landing in Alternate Law

[dream747]

Hi folks,

After so much discussions in previous threads (which are closed hence a new thread) regarding why the A320 goes into direct law after putting the gear down in alternate law so we can land it.

Did anyone notice recently there are failures in the FCOM like FAC 1+2 fault or Yaw Damper Sys fault; on certain MSNs there is no direct law upon gear extension. Coincidentally from the FCTM theses MSNs have the PFD characteristic speeds calculated by the FMGS instead of the FACs. Any correlation?

So we can land in alternate law now?

[tubby linton]

My initial response would be that this is reminiscent of the A330 which has an fmgec and no fac.It is very hard to get the A330 into direct law and if you are in alternate law you remain so after the gear is extended.

[vilas]

dream747
I will restrict myself to A320. A320 the flare mode lowers the pitch progressively to -2 degrees to give you conventional aircraft behaviour during landing. This is not possible in alternate law. so the other way is to make it a conventional aircraft by taking computers out of the way by putting it in direct law. If this was not done you would not be able to keep the stick out of neutral after flare. The confusion occurs because direct law is described as the lowest level of degradation. Now why is this not applicable to sharklet fitted aircraft with FAC and Yaw damper failures? The airbus has replied to me that in sharklet aircraft with these failures, because of the improved flight control computers the aircraft actually remains in normal law with flare mode available. If it was shown as normal law the crew might treat these failures as insignificant so is shown as alternate law.

[dream747]

Vilas thanks for the explanation. So do you mean that the flight control law remains fully in normal law or is it actually in alternate law but with the flare mode available in the new computers?

Would help though really, that Airbus insert some text in the FCOM to tell us about it! :}

[vilas]

dream747
Aircraft remains in normal law with usual flare mode.