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AF 447 Thread No. 12

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AF 447 Thread No. 12

Old 4th Feb 2017, 18:07
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Disable Autotrim in Alternate Law
AF447 | formercaptain.ca
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Old 4th Feb 2017, 19:05
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"First the airplane stalled (quit flying because the Angle of Attack was too great). Then, because of the steady back pressure on the sidestick, the autotrim wound the Trimmable Horizontal Stabilizer (more powerful than the elevators) to full nose up."

Disagree, strongly....

Follow the stick traces (both sides) then show us how the THS was "responding" to stick inputs. Instead, it initiated and sustained a smoothe, even travel to the stop...and remained in that position until impact....

Further, the Horizontal stabilizer stopped almost a full degree shy of "full travel". This suggests perhaps a mechanical issue....



If the THS were relying wholly on the stick to conform this automatic travel, it would have articulated in synch with the stick, per Alternate Law, Pitch..... (Not smoothly). To reconcile this movement would imply the FCM somehow "knew" the Pilot wanted full travel, or it was programmed to independently input full Nose Up.

"because we must know not only why F/O Robert stalled the aircraft, but much more importantly why he didn’t know he had stalled it, why he had a totally inaccurate picture of what was happening, and why there was a complete absence of situational awareness on that Flight Deck."

False. Robert did not Stall the aircraft, Pilot flying was Pierre Cedric Bonin.....who was F/O and RHS.

(Paraphrase): this author claims the a/c flies just as any other, that it has "positive longitudinal stability".
If it had, it likely would have been recoverable, instead of remaining nose high at the Stall....(the Nose would have dropped significantly, signaling the Stall, and cueing recovery....)

What about the Trimmable Horizontal Stabiliser? Calling it "Trim" is misleading. As it cranks in Nose Up, it is fundamentally changing the Angle of Incidence of the Stabiliser, not its trim. Any deviation from neutral Angle of Incidence changes the neutral point of the Stabiliser and its ability to provide a consistent downforce. In short, the character of the maneuverability of the airframe in Pitch is altered, imparting a stubborn bias to the Pitch control. At full THS Nose Up, the aircraft cannot alter its Pitch away from Full Nose Up, the elevators are essentially useless.

Last edited by Concours77; 4th Feb 2017 at 21:23.
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Old 10th Feb 2017, 17:59
  #1283 (permalink)  
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Just in:
INFO FRANCEINFO. Crash du vol Rio-Paris : la justice ordonne une nouvelle contre-expertise
http://www.lemonde.fr/societe/articl...7960_3224.html
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Old 10th Feb 2017, 19:45
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the justice ordered a new second opinion.....

As expected, nons? They can borrow mine, if they wish....s'il vous plait?

Publish 10 fevrier, 2017, cette Les familles espèrent un procès bientôt

The families expect the trial soon....

m'aider monsieur....

Last edited by Concours77; 10th Feb 2017 at 23:08.
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Old 11th Feb 2017, 10:48
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3rd Appraisal

Never is this going to end.
The other day I heard some attorney say on different case that court action too long after an event has little value.
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Old 11th Feb 2017, 18:59
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Cold Case

Never is this going to end.

Don't be discouraged.

While "defensible", the report is not conclusive... If the evidence remains covered up, or worse, destroyed, there is no statute that runs on manslaughter.

Or fraud.....
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Old 12th Feb 2017, 21:45
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What about the Trimmable Horizontal Stabiliser? Calling it "Trim" is misleading. As it cranks in Nose Up, it is fundamentally changing the Angle of Incidence of the Stabiliser, not its trim. Any deviation from neutral Angle of Incidence changes the neutral point of the Stabiliser and its ability to provide a consistent downforce. In short, the character of the maneuverability of the airframe in Pitch is altered, imparting a stubborn bias to the Pitch control. At full THS Nose Up, the aircraft cannot alter its Pitch away from Full Nose Up, the elevators are essentially useless.
Oh it is trim all right. Trim refers to the effect on the aircraft as a whole, and is used to control the aircraft pitching moment within the limits of its trim authority.

There are any number of aircraft that use this method of trim. Virtually every airliner in use today trims the horizontal stabilizer angle of incidence. Many Piper aircraft trim in this manner, as well as a number of military aircraft.

The thing that did not make sense about AF447 trim behavior was why was it possible for the aircraft to continue trimming nose up (In Alternate Law) after reaching stall AOA?
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Old 12th Feb 2017, 22:20
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Originally Posted by Concours77
the justice ordered a new second opinion.....

As expected, nons? They can borrow mine, if they wish....s'il vous plait?

Publish 10 fevrier, 2017, cette Les familles espèrent un procès bientôt

The families expect the trial soon....

m'aider monsieur....
Your French really makes no sense
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Old 13th Feb 2017, 00:31
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KayPam

Your French really makes no sense

My spelling, but the translation comes from my niece, a PhD in French linguistics.

Machinbird:

My definition of trim is mine, and it comes from flying aircraft whose Horizontal Stabiliser is fixed. In such a traditional platform, "trim" is accomplished by deflecting a "trim tab", and is used to reduce the need for constant pressure on the yoke. The tab is cranked in to establish a "trimmed" aspect for cruise.
My first flight instructor cautioned against using trim for maneuvering. For obvious reasons, imo, and 447 is a prime example of "runaway" trim.....again, automatic, no pilot input. In fact, once at the stop, it's bias NU prevented Recovery....

AF 447 was in jet upset, out of control, and auto trim cranked in full Nose Up, in and through aerodynamic Stall....once at the stop, the THS didn't budge; it held that full Nose Up "Trim" until Impact with the Sea.

In an exchange with an AE whose employer was at one time Airbus, I got a very frank admission that the THS program was a huge mistake, and needed to be changed....if the recorded data was accurate... these professionals, always with the "caveat", yes?
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Old 13th Feb 2017, 03:38
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Flight Control in the modern age

Concours77, be very careful of home grown definitions in the broader context of modern aviation.
Before you can understand the Airbus FBW flight control laws, (and the AF447 accident) you should understand C* flight control and how it operates.
Similarly, to understand Boeing FBW flight control laws, it would help to understand C*U flight control.
Check out this link for a quick explanation of the concepts:
Fly-By-Wire A Primer for Aviation Accident Investigators

So how do you think we trimmed the F-4 Phantom with a single all moving stabilator at the back end and no elevator or trim tabs and electricity only needed to change the trim setting? When you understand that, you will understand that your trim definition is impossibly restrictive.
Originally Posted by Concours77
My definition of trim is mine, and it comes from flying aircraft whose Horizontal Stabiliser is fixed. In such a traditional platform, "trim" is accomplished by deflecting a "trim tab", and is used to reduce the need for constant pressure on the yoke. The tab is cranked in to establish a "trimmed" aspect for cruise.
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Old 13th Feb 2017, 16:38
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Load factor and pitch rate demand is not relevant to this particular point. It is sufficient to base the discussion on "AutoTrim" and the need to fly manually whilst another axis is C*.

I politely reject your contention that there was "panic" or excess "fear" on the flight deck.

I thought the CVR (that released by Otelli) demonstrated that the profanity, and the reasonable questions: "But what is it doing....?" Show an engagement that belies panic.

I also reject the "PIO" determination when the roll axis got "challenging", when other evidence points to an approach to Stall dynamic: "uncommanded roll, unresponsive controls, buffeting, and an active Stall Warn" (both audio and ECAM). That the aircraft then entered an uncontrollable climb also suggests other, and patent derivations: Air Caraibes, Indonesia, Metro, etc. instead of "pilot pulled aft stick....

The report's record is derived from evidence that is subject to considerable interpretation, and there is no conclusive causation here.

Can you help with your memory of the early ACARS data? Reported by French employees of the airline, there was this: "TURBULENCES FORTES..." The system reports via satellite. The crew knew they had poor radio comms, can the crew type a message to Paris via Satellite, concurrent with mechanical reporting?
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Old 13th Feb 2017, 18:01
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I hate this conjecture that their was FEAR.
After 40 + years I can say that I have never been subject to fear during an event/incident.
BUT I have for sure had the shakes after the event/incident once one the ground.
In the air just get on with the job!
IMHO they were not frightened in this incident but obviously confused.
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Old 14th Feb 2017, 01:45
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IMHO they were not frightened in this incident but obviously confused.
Actually this was an accident, and if they were not experiencing fear on the way down with their aircraft not responding in the way they were expecting it to, then they were not human.
A big clue that they were experiencing fear related stress is that they were not hearing the stall warning alarm while it was sounding (other than right at the beginning when it chirped at them a couple of times). The ears are one of the first things to shut down under stress.
.
After 40 + years I can say that I have never been subject to fear during an event/incident.
If you can close your eyes and see the event in graphic detail, you probably experienced fear related stress and time dilation at the time.

I can vividly recall a low level jet wake turbulence encounter that rolled the aircraft ~90 degrees at 50 feet above the runway, for example but I was too busy to perceive fear at the time. Doesn't mean that the stress hormones did not kick in, because they did.

Fear is a natural human condition that creates a strong hormonal response in the body. Let us not pretend it does not exist or is a sign of weakness. It is a hidden factor in too many accidents that we seem to be tap dancing around rather than confronting.
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Old 14th Feb 2017, 09:37
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but I was too busy to perceive fear at the time.
That is what I meant. I am sure stress hormones were active hence the shakes after the event.
Fully aware that this crew possibly were not hearing the stall warning & were suffering from stress effect. But the CVR indicates to me they were not fearful per-say.
Still wonder what was meant by "we have no indications" as if I understand correctly when that was said the airspeed indications had returned.
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Old 14th Feb 2017, 10:27
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I get that after a particularly challenging landing. I relish max conditions, crosswinds, etc, and really enjoy the challenge of controlling it all and landing safely, (or throwing it away if it gets too bad). I don't feel scared during this, just engaged and focussed, but I can feel the fight or flight hormones in my system as we taxi in.
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Old 14th Feb 2017, 16:14
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Machinbird,

"A big clue that they were experiencing fear related stress is that they were not hearing the stall warning alarm while it was sounding (other than right at the beginning when it chirped at them a couple of times). The ears are one of the first things to shut down under stress."

You say that, but how do you know this? How is it you "know" they heard the Stall Warn the first time, at AP quit? How do we "know" they either "did not perceive" the following alarms, but instead were only "ignoring" them, perhaps having rejected the warnings as spurious?

This is the problem with "knowledge". Sometimes (often?) it is equated with facts....what we know is based on input....

We do "know" for instance, that the CVR data is not complete. I "know" this because the investigative agency has said so.

So you might respond, "if the crew were discussing recovery and mentioned a "Stall", that would of course be reported...."

You may assume the crew was cognizant of degrade to Alternate Law immediately? In point of fact, the degrade to AL was not memorialized until eleven seconds AFTER loss of AP and speeds.

"We've lost the speeds, Alternate Law......." (02:10:21)......

Do you recall the reported status of cockpit data? "Nothing was recorded from the Right Side of the Cockpit"?

To my knowledge, there is but one accident involving Airbus equipment where the pilots are suggested to be completely at fault.....(447)

There is on record an accident where flight data recorders were switched, the replacement recorder had falsified data.

The official record of 447 can be reasonably defended. But this reasonable defense is dependent on data that is ostensibly unavailable?
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Old 14th Feb 2017, 16:25
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Still note that many on here still do not understand airbus FBW. Note when not in direct law stick fore & aft movement is a G demand. So I suspect the software interpreted the back stick as a request for x g. So as the aircraft could not produce the x g it tried its best so ran the elevators full up & still not sensing the required g ran the stab full up. (ie followed up)(trimmed is not exactly a correct term)
In theory say a little aft stick requesting say 1,1/4g will end up with full up elevator & full up stab if that is what is required to produce the g demand of 1,1/4 g.
Not relevant here but roll when not in direct law is a roll rate demand so same applies if a small roll demand can not be met full aileron & full roll spoilers could be the result.
I will say however the real aeroplane does have some delay in producing all this.
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Old 14th Feb 2017, 16:42
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IcePack

"Still note that many on here still do not understand airbus FBW. Note when not in direct law stick fore & aft movement is a G demand. So I suspect the software interpreted the back stick as a request for x g. So as the aircraft could not produce the x g it tried its best so ran the elevators full up & still not sensing the required g ran the stab full up. (ie followed up)(trimmed is not exactly a correct term)"

That has been the point right along. The major issue for me is not C* but its pairing with Roll DIRECT. We don't know the aircraft's timing in the degrade to this obscure Law, but it May have been delayed by eleven seconds from the initial upset (StallWarn, Cavalry Charge, Master Caution).

If so, do we know the uncommanded roll was weather, wind shear, ham hand, or approach to Stall? We don't.

So after hours in AutoFlight, the aircraft splits its personality, and requires an unannounced reversion to manual? In (expected) turbulence, and bordering on jet upset at loss of auto?

Yes, the "Stab full up" is not exactly "trim"....

"I will say however the real aeroplane does have some delay in producing all this."

Precisely. Perhaps the root cause of this tragedy? Timing is everything?
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Old 14th Feb 2017, 17:51
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Concours77

It might be a good idea for you to get your niece to translate the definitive (French) version of the Final Report which differs from the English version in several respects.

In particular, in section 1.16.3 it states that the two ADRs failed between 2:10:3.5 and 2:10:05 and that the FBW reverted to Alternate 2B at 2:10:05 and stayed in that mode thereafter. So we do know the timing of reversion to direct law in roll - no supposed eleven second delay.

Then in section 1.16.4.1 it states that " lorsque le pilote automatique se déconnecte, un gradient de vent latéral concomitant (20 kt en 4 s) engendre le départ de l’avion en roulis à droite ;" so we do know the source of the uncommanded roll. Fig 64 of the French version shows a simulation of what the lateral response of the aircraft to this turbulence would have been with and without the actual pilot input. Note that this data does not exist in the English version.
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Old 14th Feb 2017, 19:18
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"In particular, in section 1.16.3 it states that the two ADRs failed between 2:10:3.5 and 2:10:05 and that the FBW reverted to Alternate 2B at 2:10:05 and stayed in that mode thereafter. So we do know the timing of reversion to direct law in roll - no supposed eleven second delay."

WE know. Because we have the DFDR. When did the flight crew know? All I can find that was reported by the investigators was the CVR: "We've lost the speeds.....Alternate Law...."

That was Robert's remark, at (I believe) 02:10:21.... Per the CVR Mike 1....

I submit that you knowing, and I knowing, and we knowing, means less than nothing...

When did THEY know, and what's missing from the CVR?

I apologize for giving you the "we".... I have a hard time not putting myself in the cockpit, and trying to suss what "they" knew, and "when"?
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