Turbine D

Now you must admit this wasn't a very tech oriented posting, was it? Dozy has been a very valuable resource in understanding the electronics of the Airbus aircraft for many of us during the AF447 saga. Your criticism tends to be a cheap shot.
Since you have recently emerged as the bright bulb on the string when it comes to technical understandings (questions when you know the answers), lets get back to technical stuff, eh? A question for you: There are 6 cues, you were taught, so as to recognize UAS. What are they, can you name them without looking them up? We are all interested in your response.
These cues, by the way, being missed by this crew, lead to non-application of the UAS procedure.

andycba

HN39:

"I wonder if the preoccupation of some posters with the THS can be traced to a misperception of its rôle. When releasing the stick in a small airplane, the elevator is released and the airplane goes to the AoA for which it is trimmed.

That is different in a FBW airplane. Releasing the stick does not release the elevator. The elevator goes to the position that will provide 1g. As long as the elevator doesn't reach full travel, the position of the THS is irrelevant for the flight path. The main difference is that the elevator moves quickly and the THS moves slowly. 1° of THS is equivalent to 1.5° of elevator (according to Owain G)."

Forgive my ignorance, but could you explain something further? - I've long been following this story as someone with a history in software development, human machine interface design, appropriate use of technology as well as safety critical engineering in computing and telecommunications. This area is also rife with mode confusion, troubles with automation and manual configuration, as well as difficult diagnosis of problems and recovery/reversion - just look at Natwest as a recent example.

I'm confused by how you are referring to a FBW airplane here in general - FBW is a mechanism to move control surfaces without direct mechanical linkages, at least for the primary control mechanism.

The implementation of FBW could have direct control surface deflection based on control input movements - e.g Airbus direct law

On the other hand, there are a myriad of control laws that can be put in place on a FBW aeroplane that can alter/filter the control inputs to produce a control surface movement to match what the designers want to achieve - be it protections, stability etc.

As I understand it, Airbus, Boeing, Sukhoi etc have their own implementations of FBW, not all the same and not all demanding 1G responses? Do all FBW default to a 1G design philosophy? And as I could understand it, airbus and boeing differ in their control law philosophy, with one being flight path stable and the other being speed stable?

So this lumping together of all FBW aircraft as following the 1G philosophy has me confused. Could you elaborate a bit further if possible on this at all for an outsider?

HazelNuts39

andycba;

My post was about the A330, the airplane under discussion in this thread. Sorry if I did not make that explicit.

thermostat

Seems to me that some folks don't understand the "auto trim" concept.
The elevator and stab must be faired (in a straight line) in order to remove the load (forces) on the control column/stick.
If the stick/wheel is moved back, the elevator moves up and is no longer faired with the stab. The pilot has to trim nose up (leading edge of the stab moves down) so as to align to two surfaces and remove unwanted pressure.
Instead of the pilot having to manually move the trim wheel, auto trim simply does it for him/her. Holding back pressure on the wheel/stick will cause the auto trim to move (trim) the stab until the two surfaces are aligned (faired).
That's what happened in the case of 447, The auto trim did exactly as it was supposed to. It trimmed the stab to fair with the up elevator. It's a beautiful system that reduces the workload on the pilot. If they wanted to recover from the stall condition, all they had to do is push forward a bit on the SS moving the elevator down and the auto trim would have dutifully trimmed nose down to the required angle. End of stall. Please stop blaming the auto trim for doing it's job.

TTex600

TurbineD, my post was as tech oriented as was Dozy's quoted post. And sometimes, someone has to stand up to the bully.

I have no idea what six clues you think I was taught. Unlike Dozy, I'm not professing to be the expert. But I do know a little and some of it happens to show that Dozy isn't the expert on all things flying.

Edit: you accuse me of a cheap shot, then drop right down to trying your own shot. I posed flying questions to Dozy because he continues to insinuate superior operational knowledge. I asked him specific Airbus quirks, not to show my knowledge but to help him realize that he might not know everything.

I've asked many times for people to think about why the crew was confused, maybe they didnt know youre six steps. You've not answered my questions about their confusion with your six steps. Go ahead and post them, some of us might learn something.

Edit #2: TTex doubles down.

Dozy assumes the role of an exasperated superior and again insults those who would dare disagree with him Where do I find your post chastising Dozy for his attitude of superiority? Why not take umbrage with his self elevated position as a board policeman?


I'll stand by the post you find offensive. And I'll ask again, If Dozy is thoroughly fed up, why does he continue to escalate the tension?

TTex600

How many accidents/incidents have been blamed on pilot fatigue caused by working too hard on trim? Or, how many accidents were blamed on pilots incorrect trim?

IOW, was the auto trim necessitated by a need to reduce pilot workload?

Machinbird

I think I understand what TTex is pointing at.
There was only a small trim change in THS position leading up to the stall, but if that trim change had not occurred, the aircraft would have sought to fly at its original trimmed speed and PF would have had to work mighty hard to slow it down to a stall. Dozy does not really appreciate the significance of this because his piloting experience is minimal.

Yes the Airbus THS trim worked exactly as it was designed to. So What? In retrospect, that might have not been the best design from a human factors standpoint.
Yes, any self-respecting Airbus pilot who could fly the thing in ALT2 law at altitude would appreciate the flight path stability offered by the current implementation of Alt2 which involves similar behavior to Normal Law in pitch and Direct Law in roll.

However a pilot who badly overcontrols an Airbus in roll and doesn't know how to stop it will have serious trouble controlling other axes at the same time. With such a loss of precise pitch control ability, the flight path stability of the Airbus becomes a liability, because it tends to mathematically integrate inadvertent pitch inputs.

Such a pilot would benefit from a direct drop to manual THS trim following loss of speeds. This essentially means Direct Law in pitch also, since Alternate law in pitch without autotrim does not make sense.

Perhaps the law of lowest common denominators (i.e. weakest pilot skills) should apply as the difficulty of flying increases. From all accounts Alt2 at altitude is not particularly difficult if one is smooth, but can be a real bear if one is using the stick to wipe the cockpit.

I'm going to offer the opinion that if AF447 dropped to Direct Law on loss of speeds, even with the crew she had on that night, the odds of arrival at the other end would have dramatically improved. Then the raw airframe's natural speed stability would have helped them avoid the low speed trap that they fell into. At least, they would not have crashed in the same manner.

rudderrudderrat

Hi studi,
All they needed to do was to disengage the autothrust and advance the thrust.
How can 3 crew members watch the speed decay to Vref -20?
Why did no one press the TOGA switches?
Alternate Law would not have saved that crew either.

"The first officer responded immediately to the stick shaker by pushing the control column forward and also pushing the throttle levers forward. The captain however, also responded to the stick shaker commencing by taking over control. Assumingly the result of this was that the first officer’s selection of thrust was interrupted. The result of this was that the autothrottle, which was not yet switched off, immediately pulled the throttle levers back again to the position where the engines were not providing any significant thrust. Once the captain had taken over control, the autothrottle was disconnected, but no thrust was selected at that point. Nine seconds after the commencement of the first approach to stall warning, the throttle levers were pushed fully forward, but at that point the aircraft had already stalled and the height remaining, of about 350 feet, was insufficient for a recovery."

ASN Aircraft accident Boeing 737-8F2 TC-JGE Amsterdam-Schiphol International Airport (AMS)

mike-wsm

Bearing in mind that the THS position had been in one steady setting during high altitude cruise, shouldn't the electronics have kept it like that and refused to move it so far so quickly without reason? Any permissible movement would be extremely slow and linked to fuel burn or movement.

HazelNuts39

I don't think that is a correct description of how the system functions. A sidestick input commands a change of flight path. The flight control system moves the control surface to satisfy that demand. If the THS had not moved, the FCS would have commanded more elevator to achieve the demanded response from the airplane, 1.5° for 1° of THS estimated by Owain Glyndwr. The elevator would have reached its maximum deflection of 30° 5 seconds earlier (see chart below). At that time the AoA was 33° and perhaps it would not have increased beyond that with the THS remaining at 3° and the sidestick held on the back stop.

I doubt that also. It would not have made longitudinal control any easier, and the PF would probably have over-controlled. And what were his targets? Would they have been different in direct law?

rudderrudderrat

@ Studi,
Have you read OEB 38 "Erroneous Radio Altimeter Height Indication"?
"During an ILS (or MLS, GLS) approach with AP engaged, if an erroneous and very low RA height indication occurs, THR IDLE and FLARE modes may engage early with the following consequences:
In CONF FULL, the High Angle of Attack protection is not available. As a consequence the autopilot will not automatically disconnect at α prot +​1 °. If the flight crew does not immediately react, the angle-of-attack will increase and may reach the stall value."

If you think a computer controlled stab trim will save your life - then you are going to be bitterly disappointed.

rudderrudderrat

@ studi,
Have you actually read OEB 38?
Oh .... Please tell me what it really means.

rudderrudderrat

Have you actually read OEB 38?
Here are a few to start with then.
Accident of an Iberian Airbus A320 in Bilbao

"the French Civil Aviation Authorities (DGAC) had issued an airworthiness directive (AD) for the A319/320 aircraft. It ordered the crews to fly at least 10 kts. faster and use only “CONFIG 3” (flaps 3) setting on approach in conditions with gusts greater than 10kts reported wind increment (max. wind minus average wind), or when moderate or severe turbulence on short finals has to be expected......
In the light of the accident occurring only four months ago, and the sometimes lengthy ‘normal’ timeframe for implementation of safety revisions after an accident, it appears to be of “amazing speed” how Airbus Industrie, - even in the absence of a final report, has already decided and performed a modification on the alpha- protection control laws. This was done in an approach “to increase the flight crew’s authority”, - as Cpt. Brandt was quoted saying by media. - A step applauded even by staunch Airbus critics among the international pilot community. A revised software version is expected to be validated this month and has already received certification by the French Civil Aviation Authority (DGAC) and the European Joint Aviation Authority (JAA). Airbus plans to implement a “rapid retrofit program” for its entire A319/320 fleet."

RetiredF4

Just to be correct, that applies only, if the aircraft was already in alternate law prior gear lowering, and has imho nothing to do with AP off. If not in alternate law prior gear down, it will land in the flare mode of alternate law. I think you know that, but others might read your post in a different way.

NeoFit

studi
And what about ORY 1994 Tarom serious incident ?
(so sorry, but it's my own hamster wheel ;-))

Lyman

Wie gehts studi...

I think I have not referred once to Boeing. I discuss THS and Autotrim because of its importance in this accident, whilst you seek to frame Bus as Victim of nasty Bus haters....

Autotrim is remarkable in 447 case for its anomalous behaviour in the tragic flight path that doomed this flight.

1. At 2:10:05, it was set to three degrees (-) NU. Throughout the climb and until STALL Warn 2, there it remained, until 2:10:48. You say, along with thermostat's elegant description of its function, that it seeks always to fair the elevators into its AoI, reducing stress on controls.

2. At 2:10:48, it started to move smoothly ( see graph IR #3), until it hit Maximum NU. IT REMAINED at MAX for the duration...

3. There has been a weak but continuous clamor that the THS' behaviour was due "insufficient deflection" by the pilot, and/or short duration of input via SS.

4. Which is it? Is it insufficient controls NU by the pilot? Or is it "Pilot pulls like madman" on SS, and the THS behaviour is unexplained?

5. Some explanations for this dormancy of the HS:

a. Overspeed protection, THS inhibited.

b. Load factor exceeded for Autotrim, (spike of +1.65G in climb)

c. Direct Law

d. A mystery, and none of my business....

Aufwiedersehn, Lyman

EDIT.... It is not incorrect to state that for purposes of discussion, one may say that there was no Autotrim whatsoever post autopilot loss, 2:10:05.

It was fixed for 43 seconds as this aircraft climbed to STALL....it then cycled smoothly to its functional limit, and remained there until impact, at 2:14:28.

I know you are a big fan of Autotrim, so....where was it?

I have belabored this anomalous failure as to the effect it must have had on the pilots. In phase 1, the CLIMB, the was no trimming. In PHASE 2, it was maxed full NU.

PF BONIN has to master the controls in two regimes, the climb, elevators only, and the fall, FULL NU THS plus elevators. In upset, and then LOC, he has TWO PITCH authorities to acclimate to.

No problem, any monkey can do that? Just as the a/c is about to Stall, the Slab
Actions to provide trim FULL NU. The a/c remains NU, dissipates some very valuable energy, and drops in free fall (still NU). You could do that in your dreams?

A casual observer could make the claim that the STALL was forestalled, then caused, by the THS.

bubbers44

Why all these laws? Are pilots flying these machines or robots? All my flying career it was so simple, push forward it goes down, pull up it goes up and pull up too much it goes down because you are totally stupid. Very simple law.

Organfreak

@Studi:

What had been under discussion was Airbus flight-control logic in this particular case, AF447, and the possibility of improvements to the software logic. (Admittedly very difficult to suss, given the lack of specific information about exactly what the pilots saw and responded to.) As you yourself admitted, there is always room for improvement in almost any system you could think of, and here, we were not talking about improving Boeing's flight-control logic.

Your comments have devolved this into a discussion of A vs. B, in general. Not helpful at all, though always fascinating and tempting to get into. Perhaps this should have been a new thread: "Ten thousand views on A vs. B." The very unfortunate accident at Schipol really has very little to do with what happened to AF447.

'Tis true that there was, very obviously, a training/knowledge problem on the flight deck (AF447), but that does not mean that there was no problem whatsoever with the A330's logic. I'm upset by arguments such as yours (and Dozy's) because they would remove any possibility of safety improvements, which have to be a good thing. "It's good enough, in fact, it is wonderful," you seem to say. Scary stuff.

DozyWannabe

It was a throwaway comment made very late at night, after a long day, referring not to the subject at hand but to a (brilliant but not very well-known) police procedural TV show.

I was saying "If you don't know who Bayliss and Pembleton are, you probably wouldn't get the reference" - nothing more. It was supposed to be a comic aside to prevent things from getting too serious!

Lyman

studi...


Quote..."It is interesting what you say, but from a pilots point of view, it is irrelevant if a pitch demand on the side stick is executed by elevator or stabiliser, as long as it is executed. This was the case, the aircrafts pitch followed Bonins input."

That too, is interesting. The Stabiliser, in Full NU adds 13 degrees to the elevators deflection relative to the airstream. I submit that had a great deal to do with the extreme high AoA into and through the STALL. At deflection of 30 degrees, plus 40-60 AoA, the elevators are acting more like spoilers than elevators. At the highest, they are lift fences at ninety degrees to airflow. All drag, no lift.

At three degrees deflection, the elevators would be pumping hard, without the trim that a pilot would expect. Now trim is visible on the wheel, but that would possibly serve to confuse..... If pilot susses no trim, well. That is evidence of DIRECT LAW. What else could it be? A Trick? Not really, but false evidence, appearing "Real".

At the extremes of deflection, the AOA could be expected to drop rapidly, and increase likewise, making for a bit of a wild ride.