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Old 10th Dec 2012, 14:33   #41 (permalink)
 
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Direct law is not an attitude demand, it is an elevator angle demand, so it is more like an AoA demand.

The reason to release the sidestik, erroneously, is because in normal law, what we do all the time, is to trim the airplane in flight path by releasing the sidestick. So when we mistakenly we do that, in direct law, it is very nasty for the airplane, pax and everyone. After many years in the bus that is what happens to many, even if they have thousands on conventional types.

The flight path stable, trimless airplane is very easy and natural to fly, but different to the conventional speed stable, trimmable airplane. When you are used to the A320, direct law is unnatural. It wouldn't be if it had artificial feeling. Being spring loaded to neutral makes it absolutely non natural, non conventional. If you come from 10,000 hour flying the 737 you will get to normal law like a duck to water, but not so with direct law. Direct law sucks. Many think of it as a reversion to conventional and it is not. It is a very degraded control system, and it requires a lot of concentration to fly the thing decently, and most don't fly it decently, I have to say. A conventional airplane out of trim is easier to handle than a direct law 320 out of trim. It is in manoeuvers like the Go Around when you see this more clearly. When the airplane is in trim you can make gentle turns, climbs and descents. When you go out of trim things are much different because you can't feel the airplane properly. Trimming like in the Microsoft FS is not what a pilot conventionally does, even if airbus says it is.

Direct law instead of alternate law is a dangerous and silly thing to do. Direct law is the most degraded control law. It is not something you revert to. It is something you can't help, an abnormal situation with risks, similar to a 767 with faulty artificial feel.

English is not my first language, maybe dangerous is not the adequate word.
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Old 10th Dec 2012, 17:20   #42 (permalink)
 
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Quote:
Originally Posted by M2002
A conventional airplane out of trim is easier to handle than a direct law 320 out of trim.
What about simply flying them in trim then ... be it A or B.

Quote:
Direct law is the most degraded control law.
No - Mechnical Backup is - And that one is tricky.

Quote:
After many years in the bus that is what happens to many, even if they have thousands on conventional types.
Speak for yourself first, again, what is your experience outside of the bus ?
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Old 11th Dec 2012, 08:35   #43 (permalink)

 
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I've flown the Sim in Direct law and..........shock horror it's not that hard to do!!

Or dangerous!!
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Old 11th Dec 2012, 08:49   #44 (permalink)
 
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Mechanical back up is not a control law, it is just a mechanical back up. And even worse than that you have triple hydraulic failure, where the only means of control would be differential engine thrust, and maybe pax seats shifting...

My experience with non airbus is over 1,000 in Citation VII (direct mechanical flight control system) and a few in the B767. I know how a conventional airplane flies. I also have a few hours in the microsoft FS, which happens to be similar to A320 direct law. A joystick spring loaded to neutral and a trim wheel.

It is not that you are going to die because of flying in direct law, but there is risks.

And my point: it is NOT a conventional flight control system. Unless MS FS is... It is a crap of system. That is my point, and I will not willingly "revert" to it if I have a nice, closed loop, flight path stable, simple alternate law.
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Old 11th Dec 2012, 12:29   #45 (permalink)
 
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Quote:
Originally Posted by M2002
Mechanical back up is not a control law, it is just a mechanical back up.
Still listed as the last level of reconfiguration :
Quote:
Depending on the type of failures affecting the flight control system, or its peripherals, there are 3 possible reconfiguration levels:
  • Alternate law (ALT 1 or ALT 2)
  • Direct law
  • Mechanical
As you already evaluate Direct Law at risk, how would you feel under Mechanical then ... ?

I find it surprising you widely comment on Direct Law as being dangerous or at risk but don't comment on the very subject of the present thread which is :

"Under normal flight conditions (in normal law), if the Alpha Prot activates and Mach number increases, the flight control laws order a pitch down of the aeroplane that the flight crew may not be able to counteract with a sidestick deflection, even in the full backward position."

Here we have the 'dangerous' one ... IMO of course.
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Old 11th Dec 2012, 16:35   #46 (permalink)
 
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Very true.

When sensors go rogue and the system cannot reject them and the wrong information is used by the system, danger is extremely high.

When that happens it is better to revert to alternate law, by getting rid of the rogue sensors. No need for Direct law. But if it takes to go direct for whatever reason, then don't hesitate, of course...

in mechanical law, I would feel OK if I expect to recover something and go into direct or alternate. But If that is not possible, I will not feel OK anymore, for most likely I am going to die.
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Old 12th Dec 2012, 00:41   #47 (permalink)
 
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Back in 1991 at Toulouse doing the A320-200 conversion we had to fly an ILS and land in mechanical back-up, albeit in good weather, and it was doable so maybe no need to die.
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Old 19th Dec 2012, 17:44   #48 (permalink)
 
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MB2002
Quote:
It wouldn't be if it had artificial feeling. Being spring loaded to neutral makes it absolutely non natural, non conventional.
The side-stick has artificial spring feel which returns the SS to neutral.
The spring force increases with increasing displacement.
- how is that different to a conventional yoke fitted with artificial feel and hydraulically operated control surfaces? I am not a test pilot but it sounds very similar to me...

Yes, you have to pay attention when flying in Direct law - but that is true of any aircraft in manual flight. But it is not difficult for a well-trained pilot.
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Old 19th Dec 2012, 19:37   #49 (permalink)
 
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@ Microburst2002

You forgot that the electrically-ruddered A333 Adv/A345/A346/A380/A350/A400M have no more antiquated trim wheels.
Trim wheels and mechanical rudders are disappearing chez Airbus.
The electrically-ruddered Airbuses fly differently,crispier and have the additional Derotation Law.

A333Adv/A345/A345:
RTLU is replaced by PFTU and rudder deflection is increased from 29.6 to 31.
BYDU is replaced by BCM.

A380:
BYDU is replaced by BPS (no more Mechanical Law).

Last edited by Kimon; 19th Dec 2012 at 19:46.
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Old 19th Dec 2012, 20:05   #50 (permalink)
 
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@Kimon:

They may be electrically actuated, but the trim wheels are still there on this photo of an A346 flight deck (either side of the thrust levers):



Have I misunderstood?
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Old 19th Dec 2012, 20:28   #51 (permalink)
 
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stabilizer motion aural warning

A Q from the cheap seats. Is it only the MD world that has that aural callout? What would be the thinking to not have it? In an out-of-trim situation isn't it useful? Or if the stabilizer has been in motion for longer than a timeout.
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Old 19th Dec 2012, 20:38   #52 (permalink)
 
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@DozyWannabe

Thanks, DozyWannabe.
So to rectify:
No trim wheels and only electrically-ruddered: A380/A350/A400M.
Trim wheels and electrically-ruddered: A333Adv/A345/A346.
Trim wheels and mechanically-ruddered: A332/A333/A343
All A320 family w/trim wheels and mechanically-ruddered.
Not sure about A320Neo but I guess will be no trim wheels and only electrically-ruddered.

Last edited by Kimon; 19th Dec 2012 at 20:40.
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Old 19th Dec 2012, 20:48   #53 (permalink)
 
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@Kimon

The manual trim control on the most recent Airbus types has been moved to a switch on the sidestick, in the manner of the 744.
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Old 19th Dec 2012, 21:00   #54 (permalink)
 
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What was the procedure for this type of event before the reported incident on EVA Air ?
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Old 19th Dec 2012, 21:06   #55 (permalink)
 
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It's reasonable to presume this is the first incident of this type, as the AoA probes referenced are a new fit item. As such no procedure existed prior (nor was there any need for it).
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Old 19th Dec 2012, 21:22   #56 (permalink)
 
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@DozyWannabe

Fitted to previous FBW Airbuses to give pilots a manual reversion option in the event of a full failure, trim wheels are replaced by a pitch trim switches on the aft of the pedestal.
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Old 19th Dec 2012, 21:28   #57 (permalink)
 
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It would appear that beefing up redundancy in terms of electrical actuation (and relying more on electrical actuation as a result) is an industry-wide trend.
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Old 20th Dec 2012, 01:34   #58 (permalink)
 
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Quote:
It's reasonable to presume this is the first incident of this type, as the AoA probes referenced are a new fit item. As such no procedure existed prior (nor was there any need for it)
The issue of corrupted data that can mislead the flight control computers is certainly not new. But a new dimension is reached with Airbus as the protections take over, and so, based on those corrupted data.
No need for a procedure Dozy ? Would you still think that way if you were a pax on that 330 ?
I don't know which crew had to deal with that AoA issue and how they did react but privately, they probably have a lot to say now, not everything being necessarily nice to Airbus ...
Did you say EVA air jc ?
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Old 20th Dec 2012, 01:59   #59 (permalink)
 
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Quote:
Originally Posted by CONF iture View Post
The issue of corrupted data that can mislead the flight control computers is certainly not new. But a new dimension is reached with Airbus as the protections take over, and so, based on those corrupted data.
Bad data messing with autoflight is certainly not Airbus-specific. With Airbus FBW, the protections do not "take over", they limit and constrain attitude.

Quote:
No need for a procedure Dozy ? Would you still think that way if you were a pax on that 330 ?
Read what I wrote - this incident appears to be related to a new piece of equipment applied to the AoA vanes. Prior to the installation of this equipment this did not happen. If I were SLF on that flight I'd hope something would be done quickly (which it has been), but one can't really ask for more than that!
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Old 20th Dec 2012, 06:56   #60 (permalink)
 
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Quote:
Bad data messing with autoflight is certainly not Airbus-specific. With Airbus FBW, the protections do not "take over", they limit and constrain attitude.
Bad data is indeed a problem with any FBW design. It still seems that the AB design is prone to create some very unforgiving conditions when seeded with bogus or unexpected information (Perpignan comes into mind). Not sure if there is really a way around it or if it is the price to pay for advanced flight automation.
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