Airbus Control Laws

[rich49]

Hiya,
On the Airbus, if alternate law becomes active, and then the conditions for normal law rengagement are met again, does normal law become active again or does alternate law remain active, ie: Normal Law can never be restored once lost?
Also, if all the PRIM and SEC computers were turned off, what would happen? Would the aircraft go into direct law and the flight controls be controlled manualy? Then what would happen if they were turned back on, would normal law restore itself?
Thanks
Richard

[GearUp CheerUp]

If you were to turn off (or lose) both ELACs and all three of the SECs then you would be left with mechanical back up where the only controls available would be the rudder and the manual pitch trim. Restoring any one of the computers would put the aircraft back into direct law. Depending on what and how many are failed will determine whether the aircraft is in Alternate law (with or without protections) or Direct law. :confused:

[GO DIRECT]

Hi, I saw it in the sim last night so here goes.

Turning off the 3 PRIMS will give you an Amber message saying Manual Pitch Trim, note sidestick still works.

Turning off SEC2 now will give you a Red message Manual Pitch Trim, note sidestick still works.

Turning off the SEC1 now will give the same message as when you turned SEC2 off but now you don't have the sidestick available.

Now it is suggested that the Capt flies the rudder and pithch trim wheel and the F/O goes manual thrust and flies the N1% as called for by the Capt.

Regarding control laws, Normal law of course will give you all the Airbus protections. Alternate Law 1 & 2 gives you Load Factor protection and highspeed protection, but your Pitch Protection is lost. In Alt law 1 your low speed protection is lost, you don't have alpha floor and you risk stalling if you aren't careful. However Alt law 2 is the same as Alt Law 1 except that the failure of 2 ADRs causes loss of the low speed protection and loss of 3 ADRs causes loss of the high speed protection also. In Alt law 1 you have angle of bank protection but in Alt law 2 you dont.

Direct Law is No load factor protection, No pitch protection, but sidestick moves although you need to use manual pitch trim. No AoA protection, or highspeed protection, or Angle of bank protection either.

Mechanical backup is now the last resort using the mechanical trim wheel to control the pitch and the rudders to direct the aircraft laterally.

Basically that translates down to the point that, Normal Law doesn't need trim because you are demanding the computers for that specific control input. In Alt Law the sidestick commands control surface directly, which is the same as a conventional aircraft almost, which of course you need to trim. Direct law is now the conventional aircraft as Altn Law but without limited airbus protections, finally Mechanical backup is total loss of the side stick input.

Clear as mud I hope.

GD (330):E

[AhhhVC813]

Er, GD, Alt Law 1/2 are not directly control linked (conventional). In Alt Law 1 pitch is alternate but without protections, roll can be either normal or direct. Only in Direct Law is the sidestick effectively coupled to the controls, pitch trim is manual and the aircraft is conventional in control.

[stillalbatross]

Go Direct, the rudder's not mechanical any more on the 346. :(