Is it possible to stall an Airbus fly-by -wire aircraft in Normal Law ?

[DozyWannabe]

Originally Posted by A-3TWENTY

Supose you are taking off and suddenlly your speed (CApt and FO) goes to 400 Kts.It means you had an ADR 1 and 2 disagreement but since they agree between them , the ADR3 was rejected.So you`ll keep NORMAL LAW.

Can anyone offhand think of an occurrence where that kind of ADR scenario could happen? If both pitots were blocked prior to takeoff then the non-normal speed crosscheck should result in an RTO. I can't think of a way that both pitot tubes could suddenly fail and get the same values after takeoff but prior to climb phase (which is presumably what you're talking about).

[italia458]

I'm somewhat butting in here but I'm extremely surprised at the lack of knowledge of pilots who are flying these Airbus airplanes. I personally don't fly Airbus (my dad did) but I'm an instructor pilot and the lack of understanding of the aircraft systems in my mind is a serious issue. Why haven't you figured out the aircraft systems while in ground school? Shouldn't these types of questions be sorted before being allowed to fly on the line? This lack of understanding of aircraft systems seems to be a major cause to the AF accident. If your passengers were reading this I don't think they would want to stay on your airplane. I'm seeing a decline in the quality of pilots that are completing the training courses these days and it's quite disconcerting.

It's not just the person who started the thread but all the people responding. Why can't someone respond with a reference to an Airbus document? People are just throwing in their own experience without answering the question, regardless of how vague it is.

EDIT: If you're going to tell me I forgot to see the FCOM reference two posts above, you're missing the point.

[CONF iture]

italia458,

Truth is that the Manufacturer made the aircraft far more complex in its concept that you would think, and IMO, unnecessarily.
Information for an initial is kept to a minimum.
Airbus documentation alone is far to say all ...
Just look at the number of Airbus threads here on PPRuNe compared to the other big player.

DozyWannabe,

The scenario as initially presented by backofthedrag is not that far fetched.
Also, who would think that 2 AoA vanes would lie at the same time to silently discredit the third one which was the only one to actually work properly ...

[amos2]

Err!...the question was, "will an Airbus FBW a/c stall in normal law?"

In respect to the A320, the answer is no!

Can we now move on?

[DozyWannabe]

Originally Posted by CONF iture

Also, who would think that 2 AoA vanes would lie at the same time to silently discredit the third one which was the only one to actually work properly ...

If you're talking about XL Perpignan, then like the Aeroperu crash, the initiating factor was shoddy maintenance. You'll find that even the old hydro-mechanical or electrical systems had similar rules for redundant operations but the rules were implemented in hardware rather than software.

As for complexity, the force-feedback logic on a 777 is way more complicated than anything on the A320-A340 series and I very much doubt your average line pilot understands how that works either.

[CONF iture]

Originally Posted by DozyWannabe

As for complexity, the force-feedback logic on a 777 is way more complicated than anything on the A320-A340 series and I very much doubt your average line pilot understands how that works either.

But obviously, does not bring the Amount of threads that the Airbus 'Protection' system does ... Why is that ?

[yardman]

If you're in a climb and both the captain and FO's pitot tubes become completely blocked, by ice for example, they will in effect turn into altimeters. This will manifest itself as an increase in IAS. The Airbus will remain in normal law because the output from ADRs 1&2 will be the same. Once high speed protections become active the nose will pitch up and cannot be overridden by sidestick input. The aircraft may continue to pitch up to the normal law limit which is 30 degrees nose up. It WILL stall.

The only way to avoid this situation is to force the plane into alternate law, preferably by turning off any two ADRs. All of the can be deduced by reading the A330/340 FCTM Unreliable Airspeed section and also the QRH ADR Check Procedure.

Yardman

[AlphaZuluRomeo]

Originally Posted by yardman

If you're in a climb and both the captain and FO's pitot tubes become completely blocked, by ice for example, they will in effect turn into altimeters. This will manifest itself as an increase in IAS. The Airbus will remain in normal law because the output from ADRs 1&2 will be the same. Once high speed protections become active the nose will pitch up and cannot be overridden by sidestick input. The aircraft may continue to pitch up to the normal law limit which is 30 degrees nose up. It WILL stall.

No. Sorry Sir, I beg to differ.
The aircraft may continue to pitch up to the lower the following normal laws limits :
- AoA
- Pitch
The AoA limit is very likely to be the first reached. The flight controls computers, detecting that, will override the pitch up order (per overspeed protection) and replace it with a pitch down order (per AoA protection) aimed to maintain AoA at or under AlphaMax value.
As for the plane, it will NOT stall.

[yardman]

AZR,

Sir, you are in fact correct about AOA protection having priority over all the other ones. I stand corrected. Thanks for the clarification.

Yardman

[Bus Driver Man]

Originally Posted by skidbuggy

Say you're on an approach, fully configured, around one thousand AGL (irrespective of local terrain). Now there is an incipient RA fault that causes the jet to think that it is a 40' RA and the jet goes to flare mode with the Autothrust reducing to idle... Given that scenario I would think that it is possible to stall the jet in Normal Law.

There is no auto reduction of thrust during the flare in a FBW Airbus with the auto-thrust on. Thrust levers are in a fixed position with A/THR on.
Thrust reduction is always done manually after the "retard" call-out.
In case the pilot doesn't do this, the auto-thrust remains in "Speed" mode and will even increase thrust to maintain speed.

See TAM flight 3054 crash. (I think airbus changed the spoiler logic after this crash. But anyway, the cause was, like many Airbus accidents, bad understanding and handling of the systems.)
TAM Airlines Flight 3054 - Wikipedia, the free encyclopedia

The scenario you gave, is like the one of the Turkish Airlines crash at Schiphol. In the B737, the thrust is automatically reduced to idle during the flare.


BTW, you can stall an Airbus in Normal Law. With severe ice accretion on the wing.
When your max AOA is much smaller than your max AOA on a clean wing.

[CONF iture]

Originally Posted by Bus Driver Man

There is no auto reduction of thrust during the flare in a FBW Airbus with the auto-thrust on.

Yes there is in case of automatic landing.

[Bus Driver Man]

You're right, my bad.

[chubbychopper]

Italia458,

I too am amazed of the apparent lack of systems knowledge among those Airbuspilots who post here. It's not only on this thread, but almost all threads related to Airbus include a variety of different opinions that serves to demonstrate both the complexity of the type, and the probable ineffectiveness of the type rating training syllabus.

[Clandestino]

Dear Itaila458 & Chubbychopper.

Please do yourselves a favour.

Scroll this page all the way down. You'll find red warning there. Now gaze upon it.

There is no logically valid path from "Someone writing about Airbus on anonymous forum does not understand its systems very well" to "Airbus is very complex and training on it is ineffective"

So can the Airbus be stalled in normal law?

Yes, it's possible but it's extremely improbable. For all practical purposes, chances of achieving such bizarre circumstances that alpha prot is overwhelmed are virtually zero. Unless one forgets to cover alpha vanes while pressure washing the bus, that is.

You have to understand well: general theory of flight, meteorology, how systems generally work (especially flight controls and instruments), statistics and FCOMs to make sense out of my stark statement, though. To paraphrase Euclid: there is no royal path to aeronautics.

[italia458]

Clandestino, I can see absolutely no correlation between my post and your reply.

The point in my comment still stands.

[Skittles]

Italia458;

You fail to take into account that this is a discussion of a scenario which should not really be able to happen, or at least has never been experienced without an accident.

This thread is not discussing standard operating procedures, it's saying that;

- If this broke
- If you got this wrong reading
- If the pilot spilt his coffee on his lap at a crucial point

...then would this possibly be able to happen?

I see no reason to call into doubt the competence of anybody who has posted in this thread.

[DozyWannabe]

Originally Posted by CONF iture

But obviously, does not bring the Amount of threads that the Airbus 'Protection' system does ... Why is that ?

(Sorry I didn't reply earlier...)

Because it's not common knowledge to the average pilot or aviation enthusiast of the type to frequent this site, much less the general public.

The reason for this is that the advent of the A320 came with a certain amount of mainstream press attention, packaged with a sensational story about a "computerised plane that can override the pilot" (paraphrased). The B777's launch was more muted, but Boeing went out of their way to emphasise the more traditional control layout - filtered through the press lens this led many to believe that the B777 wasn't even FBW.

The idea that the logic determining the force-feedback responses likely took as many, if not more lines of code to perfect than the entire Airbus FBW control system does not a juicy news story make, and so it's only people who take an interest in that kind of thing that are likely to be aware of that.

I suspect the other reason is that because of the way the press presented the A320 - essentially claiming that it might be the first step towards putting human pilots on notice (which was as much complete horlicks then as it is now), a minority of pilots automatically decided that they didn't like the A320 and the series that followed, and used the "complexity" argument as one of the ways they could denigrate the concept and the aircraft.

[boeingdriverx]

you can stall an airbus fbw in normal law if all aoa vanes are stuck at a normal aoa value. there is also another case and that wil be when all pitots are blocked at the same value.

bd

[italia458]

Skittles... I agree that it's not say, discussing SOPs. However, reading through the posts on here I was commenting on the lack of knowledge that I believe should have been covered in training, but either way it should be known, in my opinion, before flying the airplane.