BrouAviation
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Joined: Fri Jun 05, 2009 6:31 am

Airbus FCS: Possible To Change To Direct Law?

Fri Mar 26, 2010 10:49 pm

Hey guys,

For school and my own interests I am looking for an answer to the following question:

Is it possible for Airbus A32/3/4/8 pilots to change to Direct Law on demand, when all systems are working properly? I came to this question after seeing the A380 performing it's maneuvres at Dubai, Le Bourget and the lot, where they really seem to push this fat bird to its limits. Amazing sight! I then wondered if this was within the normal law flight envelope, or would they change to direct law for this maneuvres.

I looked into the A320 FCOM, but I couldn't find an answer. Anyone with knowledge and experience around, willing to share it?

Thanks,

Erik
Never ask somebody if he's a pilot. If he is, he will let you know soon enough!
 
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Starlionblue
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RE: Airbus FCS: Possible To Change To Direct Law?

Sat Mar 27, 2010 12:25 am

You probably can by pulling some circuit breakers. )

As for air shows, I'm pretty sure you can do that in normal law. It's not really that restrictive. You just can't stall, bank at more than 66 degrees or pull so hard that the plane breaks.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
tdscanuck
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RE: Airbus FCS: Possible To Change To Direct Law?

Sat Mar 27, 2010 2:33 am

Quoting BrouAviation (Thread starter):
Is it possible for Airbus A32/3/4/8 pilots to change to Direct Law on demand, when all systems are working properly?

Sort of. See pg. 63 here for the controls:
http://www.smartcockpit.com/pdf/plane/airbus/A320/systems/0031/

And pg. 46 for where you end up with various failures.

If you deactivate all the flight control computers *and* the inertial reference units, it should go to Direct.

You can see the relevant controls in this shot:
http://www.airliners.net/photo/Swiss...d=b77631f068a4a9f68e8960434a5daa18

Quoting BrouAviation (Thread starter):
I came to this question after seeing the A380 performing it's maneuvres at Dubai, Le Bourget and the lot, where they really seem to push this fat bird to its limits. Amazing sight! I then wondered if this was within the normal law flight envelope, or would they change to direct law for this maneuvres.

It should be within normal flight law. I believe one of the reasons that Airbus can do such cool air show maneuvers at low risk is that they can fly the airplane right to the limits and the envelop protection takes care of keeping them in the limits.

Tom.
 
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Jetlagged
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RE: Airbus FCS: Possible To Change To Direct Law?

Sat Mar 27, 2010 2:41 am

On the A320 you can simply switch both FACs OFF (via the overhead panel) and the EFCS switches to Direct Law. Can't imagine why you'd want to though as it makes flying the thing so much more difficult.  
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BrouAviation
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RE: Airbus FCS: Possible To Change To Direct Law?

Sat Mar 27, 2010 7:37 am

Guys, thank you very much. This again shows why being member of this board is so useful. Thank you!
Never ask somebody if he's a pilot. If he is, he will let you know soon enough!
 
PGNCS
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RE: Airbus FCS: Possible To Change To Direct Law?

Sat Mar 27, 2010 3:30 pm

Quoting jetlagged (Reply 3):
On the A320 you can simply switch both FACs OFF (via the overhead panel) and the EFCS switches to Direct Law. Can't imagine why you'd want to though as it makes flying the thing so much more difficult.

On the A-320 turning both FACs off puts the aircraft in Alternate Law. Subsequently extending the landing gear then puts the aircraft into Direct Law. This is how we demo stall behavior in the sim. If the aircraft had the gear down when you turned the FACs off the control law would degrade to Direct.

The airplane is still very easy to fly in Alternate Law; Direct Law is much more of a challenge, particularly in the apporach to landing stall (and recovery) scenario.

Quoting tdscanuck (Reply 2):
It should be within normal flight law. I believe one of the reasons that Airbus can do such cool air show maneuvers at low risk is that they can fly the airplane right to the limits and the envelop protection takes care of keeping them in the limits.

Yes, indeed. The flight envelope for Normal Law is PLENTY big to do very impressive airshow routines with confidence.

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