Location: Quite near 'An aerodrome somewhere in England'
Posts: 20,187
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I know what the FCOM says, but the airplane in direct law is NOT turned into a conventional airplane.
The significant change is from manoeuvre demand to attitude demand. However, the control system doesn't provide any stick force per G gradient, neither does it provide any Q-dependent feel. So perhaps not all that conventional?
beardy, I note your post. However, I remain somewhat exasperated by the....let's call it 'unusual' English used by Airbus in many of their publications.
However, all that changes in case of go around. Then, it is difficult to switch my mind to direct law, so I find myself releasing the sidestick (springloaded to neutral) after inputs, which equates to make brisk inputs back and forth, like jerks. If more angle the input had, the worse. Imagine a conventional 767 where there is no feedback from the yoke, but it will return to neutral if you release it.
But the Question is why would you release it in the first place as long as a pressure on it is necessary to maintain a requested attitude ?
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Normal law is much more conventional than direct law, in my opinion.
Which brings me to the next question : What's your experience really outside that airbus ?
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With practice you can fly direct law quite decently, but you have to actively think so that your instinct and habit doesn't put the airplane at risk.
You don't put your airplane at risk if your own way is by adopting brisk inputs back and forth, at most you make people sick in the back.
IMO you clearly need to reevaluate the basic behind piloting but also your notion of DANGER.
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.
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.
Mechanical back up is not a control law, it is just a mechanical back up.
Still listed as the last level of reconfiguration :
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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.
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.
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.
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.
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).
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.
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.
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).
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.
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.
