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3rd Jun 2011, 19:50

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100kt down and 107 G/S means it was "flying" at 140KIAS, albeit at 60° AoA.
Gee Capn Bloggs, I'm a gurl and I can do math and estimate better than that. 100kt horizontal and 107kt vertical would be less than 45 degrees from horizontal by a small amount.

10912' per minute is 107.75305 knots if you work it out to an unwarranted degree of precision. So the velocity was about 151 knots at very nearly a 45° angle with horizontal.

(It's handy with tabbed browsers to keep this link open when discussing this accident. It really helps avoid foot in mouth disease. It's not impossible, as I probably prove. But it does help. The other two good links are here and here.)

3rd Jun 2011, 20:10

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The velocity along the flight path (FPA -45), as you say, was 151 knots. The KTAS if sensed at the aircraft would have been around 89 knots, as MM43's geometry clearly shows.

3rd Jun 2011, 20:20

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It ain't "simply"

from a recent contributor:

In this case it's simply:

Normal Law -> All systems go, you can rely upon the protections
Alternate Law -> There's something wrong - protections will try to help you but if you need full authority it's there.
Alternate Law 2 -> You're missing data required for the protections to work, but you've got full pitch and trim authority via your sidestick and thrust authority via the levers.
Direct Law -> Exactly what it says on the tin.
First of all, I do not know of a single FBW system that acts in the same manner as the "old" hydraulic control systems we got used to starting in the 1950's. No mechanical connection to control surfaces, and the only feedback was body rates ( your own skinny butt, not an inertial or rate gyro). So the manufacturers did their best to give we lowly pilots a sense of feedback via springs, pneumatic bellows, etc. They also added things between we pilots and the actual control surfaces such as pitch and roll and yaw dampers, as we were moving from the old days to new designs operating at high speeds and aero effects the older planes dealt with, like Gooney Bird, P-51, Aeronica Champ, et al. Those in-between things helped to keep the pointy end forward and really helped in turbulence or near-stall conditions.

The big difference with the Airbus and the Viper FBW system compared to "simplistic" descriptions of FBW is you can never get "direct" control of the control surfaces via the computer. Well, not so fast, Gums. In the Viper, we DID HAVE A WAY to bypass the computer corrections and gains via a manual pitch override function. That thing acted like the "old" hydraulic control stick/rudder. Not recommended for the heavies, and only reason we got it was we found out we had an unusual flight condition that the computers couldn't handle. We still were at the mercy of the computers for directional stability and lateral stability. And for the "faithful" believer in the reliability of a well-designed computer system, how come they did not allow for this in the beginning?

The Airbus FBW, as in the F-16, F-22 and F-35 do not "simply" provide electrons to command the hydraulic actuators. The computers use air data, body rates, known aero characteristics, etc. to "tailor" the control surface movement in both rate and amount of movement. So this is vastly different than the "old" systems most pilots are used to and the skills they mastered.

What is this fascination with "protection"?

Beats the hell outta me, but I would rather educate the pilots that the jet "allows" this and that, and it will limit your inputs according to "its" idea of what you should be commanding.

The Airbus reversion sequences and all the "protection" and various control laws could be appropriate for a pinball wizard or drone operator. But they need better human engineering and human education as to what happens when this system goes south and what aerodynamic conditions require less "protection".

This discussion prolly needs to be moved to a separate thread in order to allow others to question who was in what seat, what pilot actions could have resulted in roll or pitch angles, what time the ACAR's transmitted a message, the bad weather in the area, etc.

3rd Jun 2011, 20:23

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Possible reasons for roll when AP disconnects in ALT 2....

Fuel imbalance
Asymmetric thrust
Rudder position
Roll demand
Aileron or spoiler position
Icing

Any more, anyone?

And responding to ventus45....

The autopilot would have been performing rudder inputs to maintain heading.
The autopilot uses bank angle to control heading. It applies rudder to maintain balanced flight. If this is done as yaw damping the rudder pedals do not move.

Would the rudder freeze there ?
No.

A few pages back, someone noted that Airbus pilots don't usually have their feet on the pedals in the cruise.
But once PF was flying manually in ALT 2 he would have his feet on the pedals.

Given that the BEA do make a point of emphasising the "continuous" left stick, and since they also emphasise there were no engine issues to support any asymetric thrust induced yaw
I must have missed this "emphasis" - can you point me at a quote from the BEA?

Is it possible, that simply failing to press that button to ensure the rudder was zero
If the pilot needs to adjust the rudder trim he uses the rudder trim switch. When the AP disconnects it is not a requirement to press the "zeroing" button.

3rd Jun 2011, 20:37

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Originally Posted by rudderrudderrat
"During unreliable air speed whilst the crew held the wings level using constant left roll input, but with a mistaken light back pressure, it trimmed the aircraft fully nose up in response - without them realising. That's bad."
We've been making rather little note of the important FDR detail, RHS is not recorded. The plane was being flown from RHS, apparently. So that does conjure the notion that RHS, PF, was seeing something vastly different from what was recorded.

I am not sure probes will ice the same way. If the drain hole on RHS clogged PF would have seen a significant (17%) increase in speed. That could be the reason for the initial pull-up. After that the RHS speed indications may have been too highly varied to be used. If the AoA got very large then sensor_validation's note about pitots being straight ahead sort of devices suggests the real airspeed was unknowable in the RHS of the cockpit.

I am wondering if there is a scenario that experienced pilots can concoct that could explain the PF's actions presuming he was a fully qualified experienced pilot, with or without any valid airspeed indication.

3rd Jun 2011, 20:44

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Originally Posted by TyroPicard
But once PF was flying manually in ALT 2 he would have his feet on the pedals.
Should, and one would hope that is a reflexive and trained reaction.

(To play devil's advocate ... one would presume that pitch and power is the response ... but that does not appear to be the case. So it's hard to be sure, puzzle pieces missing ... )

OKC:
The velocity along the flight path (FPA -45), as you say, was 151 knots. The KTAS if sensed at the aircraft would have been around 89 knots, as MM43's geometry clearly shows.
At what altitude? 35K? 25K? 10K? Within 1000 feet of the surface?

Terminal phase seems to have been where the estimates are coming from, which is down low. (FWIW, as we play with our CR2's or other wiz wheels! )

3rd Jun 2011, 20:47

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rrr, the PF's first reaction was a left nose-up stick input at 2:10:05.

And after PickyPerkins' most informative post I wonder if the rolls were an attempt to diagnose if the plane was in a stall or not. Lack of roll authority is one of the "features" of a stall mentioned.

3rd Jun 2011, 20:52

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Litebulbs, we know the plane traded a lot of velocity for altitude. I worked out the simple math on that one going back to mgh and 1/2 mv^2 basics. It lost around 40% to 50% (I'm not sure of the knots to KCAS conversion here) if we presume 100% efficient conversion. Another 10% for aerodynamics would not surprise me.

(It takes a LOT of pushing these days but when pushed that hard I do have a nasty habit of "doing the math." It happens in political discussions, too.)

3rd Jun 2011, 20:56

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Flex, Picky's post is why I am starting to seriously question what PF presumably in the RHS saw on the RHS indicators and suspecting PF used roll as a stall diagnostic after the training of the day to possibly ignore spurious stall indications. It might be that visual inputs to PF were different from what we assume based on LHS only data leading to some of his apparently bizarre behavior.

3rd Jun 2011, 21:03

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It is interesting to ponder one of the themes in Perky's offering of how the two year process was kicked off, with the airline's position being ...

The airlines wanted simplified procedures which were common to all aircraft in their fleets and which were easy to teach and easily reproducible. This is understandable because you are all interested in having a standard product at the end of your training programmes.
I am reminded of an old adage: complex problems frequently have offered simple, and wrong, solutions.

Granted, the two year process hopefully hammered out most of the wrongness, but you can see a trace of dangerous group think that needed addressing from the outset. And the problem is so noted ...

Where we differed was in our conviction that there was no such thing as a standard upset and our reluctance to endorse simplified procedures for recovery from an upset. We wanted a general knowledge based approach, as opposed to a rule based one. For this, after proposing some initial actions, we talk about “additional techniques which may be tried”. This obviously is more difficult to teach. ...........
What are computers? Rule based machines. That's a source of tension, and friction, that isn't going to go away anytime soon. I concur with the knowledge based approach, and have long been an advocate of both education and training.

Might have made a lousy executive.

That said, techniques can be taught, but the opportunity and structure (to keep things standardized) has to be there.

By the way, a few years back (Within the past ten years) I ran into a USAF field grade officer who was not novice at training. He'd flown various planes, and had instructed in T-38's, and in less awesome training aircraft. His attitude was, for military pilots nowadays ... "We don't need to teach them stalls and spins anymore, we need to teach them how to avoid stalls and spins." (Mind you, when he and I were both young'ns, we'd both been taught both) He and I disagreed, as I took the position that one needs to teach both. (Whoever wants a bit of extra credit can look up the T-6A Texan II, and see if it spins or stalls ... )

It appears that the "corporate front office bean counter" attitude about training can infiltrate into the most unexpected places ...

3rd Jun 2011, 21:06

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Originally Posted by PJ2
Thanks for engaging the broader (off-topic?) view.
No problem - I don't consider it off-topic because in this game, context is everything and it is important to understand the context in which these systems were designed. With an issue that is as emotive as this to pilots, on a forum full of pilots, it's sometimes necessary to pin down what the technology should be doing to tame the wilder theories.

Although the airline wanted its full time use, (from "just after takeoff 'til the end of the landing roll", was the SOP in the first manuals until we simply fought back and got it changed), automation was just a tool, in my back-pocket to use "when-if". That was my (cantankerous?) attitude then, and it didn't change when I retired off the A330/A340.
Not cantankerous at all - prudent, I'd say. I suspect the engineers that designed and built the Airbus systems would agree.

Just to be clear because there's a lot of "I" here, I'm describing what was the case at the time, and not "holding court"...I don't like such behaviours but sometimes one has to speak out of personal experience.
And that's exactly the kind of experience that I and others on here need to build as full a picture as possible - keep it up!

During that initial period we saw a lot of "why did they [Airbus] do this?" moments. We received a few visits from AB during the introduction of the airplane into the fleet. At meetings which the entire group of guys (who weren't flying) attended, we provided our feedback from our experience. I don't want to fully describe the engagement and reception but it was dismissive and even arrogant and it was that way over a long period of time.
They certainly didn't do themselves any favours in the early days when it came to engaging with end-users by the sound of things. I'm glad it improved - about how long would you say it was before they did?

The documents posted by PerkyPerkins bear very careful reading
Will do so.

3rd Jun 2011, 21:09

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Originally Posted by ihg
Well, whatever these guy tout as "findings", I would recomment to handle with extreme care. They have an unambiguous interest in who has to to blamed.
I note the phrasing there. It is one of my pet hobby horses. Sometimes "bad stuff" happens. Sometimes there is no person to blame in any sane world. But trial lawyers always insist there is an entity (with money) to blame and that entity is other than the entity they are representing. "Somebody is always at fault and that somebody isn't me." is a most pernicious philosophy.

The more I see of this it looks like "best practices" of the time may have been wrong. Knowledge is not static. It grows. Best practices of 2009 already appear to be different from best practices of today. Holding Air anybody to blame for not following today's best practices 2 years ago is repugnant hubris. It presumes the mere men should be gods, always right and perfect.

(I suspect a good read of history will reveal that societies that live by the lawyer, die by the lawyer. Societies that live by the law (with few lawyers) survive by the law.)

3rd Jun 2011, 21:12

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CogSim, on the incredible coincidence of geometry somebody else has already mentioned airmass speed as a factor not in evidence in the equations. A fairly stiff headwind MIGHT fit better with the initial presumptions of the impact with the water.

3rd Jun 2011, 21:15

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JD, who writes the law?

Lawyers ... except in an AB (or a Boeing) where control law is written by ...

3rd Jun 2011, 21:16

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Do pilots have options?

Alex

Many good questions. Re the Pilots Authority:
The PIC always has the ultimate say in whatever he does. It has been hinted that there may be subtle pressures, or "frowns" regarding Staying the Course for fuel or time concerns. There are always alternate fields available in case of necessity; engine failure, running low on fuel etc.
The pilot can always plan to deviate around storms and if necessary unload cargo or pax to take on more fuel. He can always go or refuse to go if he considers it unsafe to do so. He'll always have to explain his actions and justify them.
He may try to clear a deviation with ATC but if out of radio contact he can always just announce his actions on "Guard" channel, which planes in the vicinity are supposed to monitor.
Or he can declare "Mayday" declare an emergency and go wherever he feels safe.
But, to charge head on into massive build-ups up to 60,000 feet is sheer madness to me.
Everything I've ever seen about thunderstorms says: "Avoid them!"

There is no question in my mind that the violence of the thunderstorm caused the ice buildups, strong updrafts to an out of control situation, that caused all of the failures, and left the pilots incapable of dealing with it.

3rd Jun 2011, 21:43

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My piloting is 4hrs , Auster, age 16, 1975 - so that is clear... Bitten, hooked, but physically disqualified to join your ranks. So here are my unbiased thoughts on
"Manual versus Automated".
Some suggest that it would make sense to let people hand fly from time to time, and that the bean counters are against it. Well, IF at any random time hand-flying (whatever that means) was better than automation, then whoever was selling automation would be out of business, and they are not, so I assume that (sorry), more often than not, Hal saves your average arse, more often than he kills you. I know, we individually accept our own mistakes and get pissed as hell when we are right and that damn computer is wrong but the passenger down the back prefer to go with the odds.

Of course, there are times when the bean counters will say it is ok to hand fly, probably when you are well rested, traffic is quiet, visibility is good, so, SO no pain no gain, what is the benefit, I have an open mind on whether hand flying in good times is enough to help you in bad times- you tell me.
Now clearly, when things get really interesting, Hal will be challenged, and with the benefit of hindsight, still being alive (cause he saved the average arse last week), we can spot the faults.

I propose the following scheme.
Flight regime is Normal or "10 years ago". Cessna produce a plane that flies like a 10 year old Airbus and every pilot gets free flights on that, hand fly all you like, push the envelope, but leave the SLF on the ground. IF you can fly better than the current Airbus then you get a job with Airbus.

Of course, there is a wrinkle, your bean counters might not let you fly the 10yr old technology, you might have to stand your own life insurance. At Paull (airfield) we had an RAF guy (navigator) who wanted to get his PPL, the RAF decided they had invested too much in him to allow him to do something as stupid as hand fly a C150!

If Automation was not better than Mr Average they would be out of business, of course there is the argument that they have moved the average down with their marketing but the statistics say that we are progressing - get on board! It is WIP, it is not perfect, it is progress.

If you are below average, say thanks to the automation, if you are above average (as are all Pprune members) then contribute your experience to the continous improvement!

In this particular crash , I think we are going to see shock waves everywhere. At these levels of reliability is is rather expensive to do (true) preventive, the most cost effective is fast reactive, I think in an ideal world we would like to think that the pitots and training had been changed after the first 10-15 cases without waiting for the big one.

3rd Jun 2011, 22:56

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Originally posted by Lonewolf 50 ..
At what altitude? 35K? 25K? 10K? Within 1000 feet of the surface?
Thought my graphic clearly stated in the title - Final Data -, i.e. FL0.

The BEA have indicated that at TOC (FL380) the pitch attitude and AoA were both 16° and the stall was established at that point. As far as I can tell the TE was traded off (as power was reduced) for increased AoA, and the RoD was initially established at around 10K ft/min and only changed slowly to a higher value as air density changed and the AoA became greater.

3rd Jun 2011, 23:03

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At what altitude? 35K? 25K? 10K? Within 1000 feet of the surface?
LW 50:

Those are just the near end game values.

I prefer think of the 151 knots as KTS (knots true speed) as opposed to KTAS. There probably wasn't much in the way of air involved at the approximate 60 degree AOA, even unblocked.

The 151 knot speed is a purely trigonometric calculation based on a report which furnished near end game ground speed and vertical speed. Nobody is blowing air on the trig tables. (Maybe some smoke however)

The 89 knots along the aircraft longitudinal axis would approximate a no wind a KTAS via KCAS inputs if the systems were functional to sense it, which corresponds to a fairly low KCAS down low. It could be somewhat more or less, however, depending on actual wind. The cosine of 16 degrees is .96 so its horizontal component is not reduced much.

I suspect the KCAS was higher with a headwind component in effect.

My only point was that the 151 knots was not necessarily Knots True AIR Speed. I am not trying to offer anything remotely relating to cause.

Math is not hard…Math is not hard…Math is…

3rd Jun 2011, 23:57

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Originally Posted by TyroPicard
Quote:
Would the rudder freeze there ?
No.
Absent pilot input would it remain deflected or would it zero itself? I think you answered the question implicitly below as "yes".

Quote:
A few pages back, someone noted that Airbus pilots don't usually have their feet on the pedals in the cruise.
But once PF was flying manually in ALT 2 he would have his feet on the pedals.
The BEA report noted the PNF commenting about ALT law. It did not say the PF indicated he was aware of this. He should have been. But other crashes indicate sometimes the PF fixates on one problem and starts dangerously ignoring the world.

4th Jun 2011, 00:02

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I think the following has to be said again :

When the flight control inputs were inappropriate, the stall warning ceased, and when they were appropriate, the stall warning reengaged …

DozyWannabe, the way you 'simplify' the Laws is not correct :
Neither of the Alternate Laws give full authority to the pilot.
Except from Alpha-Floor, thrust authority is not Law dependant.

Too many Laws which also overload Airbus accident reports ...