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AF 447 Thread no. 4

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AF 447 Thread no. 4

Old 6th Jul 2011, 21:07
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PJ2, I reviewed our posts 715-720 and your response was if he drifted one or two thousand feet high the CAS increase with trapped pitot and drain pressure could not significantly be increased. I agree but how about mach limit? That will be the first limit you hit and DJ77 said with less than a 2500 ft climb that limit would have been exceeded by a significant margin. I don't know how to verify that information but when the CVR report comes out we will know. If someone knows how please post it. DJ77, where did you find it?
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Old 6th Jul 2011, 21:11
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The only things I feel I believe for sure out of all this are that not latching the stall warning is a clear design oversight and that trimming to near the maximum authority deserves a big red light all for itself (irrespect of 'use manual trim') -that was also a factor at Amsterdam wasn't it ?

However, even if they had recognised the condition and then acted appropriately, recovery from 20000ft would have needed at least a continual sustained 2.3g positive acceleration, and from 10000ft 3.6g. A non-optimal response would have needed more by a factor. With the instruments they had with degraded protections, was subsequent recovery even likely ?

Edit: thanks HN39, merely a factor of 60 out so pls ignore the g's.

Last edited by Mr Optimistic; 6th Jul 2011 at 22:18.
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Old 6th Jul 2011, 21:22
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CONF_iture,
Are you sure the sidesticks are not visible from the P3 seat, even if you lean forwards? They are on the A320.

A33Zab, quote:
"In respect of Capt, IMO he realized exact what was going on!
After entering cockpit ordered or pulled T/L into IDLE and ordered ND inputs!
But - if F/CTL SD page was not selected -he was unable to see THS position from this 3rd seat."

The THS scale should be clearly visible from the P3 seat, I think: rather more easily than from the P1 and P2 seats, from which you would have to turn your head. In the P3 seat, it would be under your nose.

bearfoil,
My copy of the BEA Update has the PNF making BOTH statements at 02:10:16, quote:
"so, we've lost the speeds" then "alternate law [...]"

PJ2,
Thanks for re-posting that schematic, but what I was trying to confirm is that PFD1 normally gets all its data from ADR1, and PFD2 from ADR2. That seems to be the case.

Re your latest graphic of a possible PFD configuration at start of climb, are you suggesting that the PFD CAS scales had both gone blank? When the PNF announces, at 02:10:16 (before the climb),
"so, we've lost the speeds",
what does he mean? My understanding has been that he is referring to the "characteristic" manoeuvring-speed indices such as VLS, green-dot, and Vmax, not the actual (current) CAS. The "SPD LIM" flag would have appeared next to the strip. At this stage, the ADR1 and ADR2 had not been invalidated surely that came later?
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Old 6th Jul 2011, 21:34
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My thanks, Bubbers44 - not trying to be "right"... heaven knows there are enough theories floating about to fill a tanker, but wishing to have the argument at least countered so it can be dismissed, pondered, etc.

My point was, if the aircraft was essentially level, there would be no increase in indicated airspeed as a result of any blockage. By all indications we have access to, the pitch-up occurred from level flight. It is true that the airspeed may have increased as altitude increased by the former was not the instigating "cause" because the airspeed required the increase in altitude to increase in indication.
It was asked on a previous page, why TOGA if it was an overspeed?

But as just about everyone here now has pondered/asked/puzzled...why pitch-up just for an unreliable airspeed?
I suspect the Stall warning was a result of aggressive pitch up, not a cause for the PF to pull up but as it got worse, the PF (essentially) pulled more, and longer. It isn't the first time a stall warning has been associated with a hard pull on the control column.

Perhaps too, the upcoming BEA 3rd Interim will cover this and many other questions now on the board.

BTW, I have seen significantly different (lower) Mach numbers in the calculation done by DJ77, (more along the lines of the first ones he did) so perhaps confirmation of how the result was derived might be in order. I'm not qualified to do the math but the question needs to be asked. As expressed in an earlier post, I've had an increasing airspeed in climb (B767) and while it reached the overspeed limit it took much more altitude than 3000ft (FL250 > FL280 approx) to do it. Now it's thicker air and the drain may have only been partially blocked reducing the rate of increase.... ;-7
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Old 6th Jul 2011, 21:43
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Mr Optimistic;

Pls check your calcs.
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Old 6th Jul 2011, 22:13
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HN39, be warned I am an ex-physicist so admire the precision but be wary of the decimal point and I also admit they were wine and excel affected.

Edit^2: see your point, who uses feet per minute ? You are quite right, thanks and apologies to all.

Last edited by Mr Optimistic; 6th Jul 2011 at 22:46.
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Old 6th Jul 2011, 22:17
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@ GY:

Agreed for the 30s, but from his position it will be difficult to see the SS pitch inputs (maybe the L/R inputs to fight the roll oscillations).
Required some time to be informed what took place in the previous minutes?



@CS:


Disagree, the THS indication will be covered by the trim wheels from P3 seat. see picture PJ2: LINK
I've seen pictures from A320 series and here is an obvious difference with A330.
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Old 6th Jul 2011, 22:30
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Other question answered.......

These statements will clarify some questions asked.

The system compensates almost 100% for trim changes, due to speed and configuration changes. Trim
changes, due to thrust changes, can be too large for the system to compensate, and the aircraft may
respond to them in pitch, in the conventional sense, and then hold the new attitude at which it stabilized
after the trim change.
The pitch trim wheel moves as the control law compensates for these changes.
---------

IF TRIM LOCKED > 8 UP :
MAX SPEED....................................................... ............................................................ ...... 180 KT
If trim is locked above 8 degrees UP, pitch down authority may be insufficient for speed above 180 knots.
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Old 6th Jul 2011, 22:36
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PJ2, I'm not trying to be right either, just trying to figure the puzzle out. Since I am also a B757/767 guy I don't know much about the A330 and how all that stuff works, just how airplanes in general fly and wonder why a pilot would zoom climb at high altitude into a deep stall.

I looked up the speed limitations of the A330 just now and see VMO is 330K and mach .86 is mach limit. They were cruising at about 280K and M.81 so the puzzle was with trapped pitot pressure and climbing 2500 ft what would the indicated mach speed be. I have no clue. I agree if they didn't change altitude nothing would change but they apparently did. When the CVR comes out I have a feeling the overspeed warning will be well heard in the background.
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Old 6th Jul 2011, 22:48
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A33Zab, thanks.
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Old 6th Jul 2011, 23:44
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ChristiaanJ, #871

I was not proposing that any of "my" sets of data should be used on an aircraft ( even if I knew how to prepare such stuff... I don't !)

Of the cast for the "scenario", two are seated, Left and Right...

As I am sure others must have hoped, to achieve some initial, almost a gliding performance, to give TIME.

I had read a lot of the last 400 posts but got distracted reading about Birgenair's black and yellow Mud Dauber Wasp. I had had one or more in my Pitot tubes in 1969, spotted at about 80 kts at KIN. Engineer sent from Base, old catering bad, dumpped,No pax catering available,( Bank Holiday), request Diplomatic Over-flight from Cuba, fly to Toronto for food,fly back to UK using my discretion with a double crew, only a couple of days late. My Chief Pilot thought I had taken all 130+ for a sightseeing tour. It as easier to leave it at that...
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Old 6th Jul 2011, 23:47
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bubbers44 and PJ2, re CAS / Mach with trapped total pressure.

I computed them with functions from an old (but long tested) homemade personal software (hey, I can do sfwr). It is not rocket science but I don't know how to post a picture of the formulas used and I fear it would not be clear enough if I tried to edit it here so I think it is better to look at the formulas for CAS (subsonic speeds) at Calibrated airspeed - Wikipedia, the free encyclopedia and for Mach number at Mach number - Wikipedia, the free encyclopedia
To use these formulas you need:
ps = static pressure, pt = total pressure, qc = pt -ps.
p0 = 1013.25 hPa
a0 = 661.479 kts
________FL350 __ FL375 __ FL380
ps (hPa) 238.42 __ 211.48 __206.46

If anyone wants to check this and find different results, please let me know.

I find the overspeed hypothesis not very convincing because it does not add up with TOGA thrust selection, don't explain the zoom climb and I believe it was not observed in previous incidents. However perhaps it should not be completely discarded.
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Old 6th Jul 2011, 23:54
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P3 Seat

A33Zab,
The link you posted is to a photo taken from the P1 seat, probably in its aft position. AFAIK, we do not yet know where the captain sat or stood during his all-too-brief return to the cockpit. He may have managed to sit in the P3 seat, as I think you suggested.

Regret I don't have a plan of A330 seating, but the P3 seat is likely to be the one used by third crew members, including training and check pilots. It has to offer the best viewing position behind and between the two operating pilots, usually at the back of the centre console. It was my job to spend many hours in such a seat on the A320, so I'm only too familiar with the concept. You MUST be able to see everything to do that job properly, so there has to be such a seat.

Perhaps PJ2 or CONF_iture can comment.
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Old 7th Jul 2011, 00:07
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P3 Seat

Chris Scott,

According to the flight deck layout from Airbus, you are correct in that the third seat is directly back from the center console. There is also a folding fourth seat that is at an angle behind the FO right seat.
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Old 7th Jul 2011, 00:13
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@ CS:

View from Seat P3. (I linked PJ2s picture because you can see the trim wheel being above the indication)



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Old 7th Jul 2011, 00:59
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Was the aircraft stable

JCJEANT (POST #840

Hi,

Quote:
"When the autopilot and autothrust disconnect in cruise, one takes over and manually flies the aircraft. With no speed information, the last thing one should do is change anything...pitch or power.The airplane was stable just before the loss of airspeed data. "

Why always repost this speculation ?
By myself I read (and it's not a speculation .. but a fact!) the aircraft was stable because he was in a cruise flight stabilized by the autopilot and auto throttle
When autopilot and auto throttle go out of the loop .. we don't know if the airplane stay "stable"
So maybe .. instead of touch nothing (hands off) the pilot had to act immediately for stabilize the plane
Remind .. the plane immediately banked to right (unfortunately no clue about the bank angle from BEA note ....)
So will the pilot wait the aircraft go in a 30° or more bank angle before react ?

JC

Totally Agree

At the point when 447 entered "something", ALL HELL BROKE LOOSE!

Pitots iced up. Airspeed lost. A/P and A/t kicked off. 32 or more error messages sent. The Pilot warned of "a bumpy ride".
And soon after the plane entered it's ride of doom into a deep stall.
And to me the likelihood of severe turbulance and strong up and downdrafts.
If there is reluctance to "hand-fly" the plane at altitude at all, what happens to a pilot who has never done so in turbulent air.

Are all those things happening at once sheer coincidence? Not to me.

Last edited by wallybird7; 7th Jul 2011 at 01:01. Reason: punctuation
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Old 7th Jul 2011, 01:25
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Chris - I do apologize to you and to takata for scrambling my post. My underlying post meant to establish the cognizance of lost speeds and degradation to ALTERNATE LAW at a TIME certain, and not subject to ACARS delays, routes, and signal.

It was at eleven seconds after a/p dropped ( @2:10:05 ), and PF (RHS, In this I agree with takata ) assuming even a three second recognition and speech delay, the CVR establishes that the Cockpit has been made aware by one of the PILOTs that LAW change has occurred eleven seconds after a/p loss.

Could you comment on the idea that involuntary loss of the A/P due control limits exceedance means a drop not to ALTERNATE, but to retention of NORMAL LAW?

For at least two reasons the CVR is the key to a final reconcile of this accident. First, it is TIME perfect, and exceedingly capable witnesses will be heard commenting on the source and progress of the tragic crash?

bubbers44 For my money, your approach is the best I see. Incorporating as it does a connection with the flying Pilots and high altitude hazard, I think you may be very close.

Hopefully BEA will give up a bit more soon

Last edited by bearfoil; 7th Jul 2011 at 01:48.
 
Old 7th Jul 2011, 01:29
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Just a note. The BEA retrieved the fourth seat, but no mention of their retrieving the third seat. This was during the first recovery. (The other two cockpit seats were retrieved with their occupants, and it was the DNA analysis on these two bodies that led the French court to proceed with recovery of other bodies.) One can surmise the BEA may have had an interest in the straps on the fourth seat.

After Ile de Sein swapped crews at Dakar and returned, the second recovery seems to have been dedicated to retrieval of bodies. Looking back, the crew swap may have been to bring on board a team experienced with traumatic death. And it may have been representatives of the French court that were directing the second recovery phase, with the BEA more of an observer.
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Old 7th Jul 2011, 02:43
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When the PF made the "left-nose up input" (notice singular), it seemed to solve the (small) problem he had at AP cutout. The next time we are given is 11 seconds later and no further inputs have been made on the SS (that we know of) and the aircraft seems to have been in stable and level flight for that 11 seconds.

Question 1: So if it was such a drastic input to initiate a 7K/ft/mn 'zoom climb' wouldn't it have begun much quicker especially with the speed and altitude they were at?

At that 11 second point into the incident, the note is clear that "the pitch attitude increased and the plane began to climb" keeping in mind this is 11 seconds after the only known control input. Also, the wording (the pitch and the plane did X) leads me to think the aircraft did this as no other control inputs are mentioned.

Question 2: With the different protections removed in Alt law, how would the aircraft increase pitch to such a degree with no inputs? Could turbulence/updrafts be sufficient to induce such a pitch up?

About 15 seconds into the incident, "the PF made nose down inputs" (notice plural). This seems to indicate he made more nose down than up however, these multiple inputs only reduced the climb rate but did not end it. Keep in mind, the THS had not moved at this point, that comes later. The roll left and right indicate to me there was turbulence involved at this time.

Question 3: If one left nose-up input starts such a climb why were multiple nose down inputs not enough to completely arrest it? And since the PF noticed the climb and tried to correct it, why did he let it continue at 700ft/mn for the next 35 seconds?

At 45 seconds into the incident, the aircraft ran out of energy and the AoA increased, setting off the stall alarm. Thankfully, the speeds had returned to over 60K or that might not have happened either (see later on). "The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs."

Question 4: Is it possible, despite the PNF telling PF Alt Law, the PF (whose speeds may have been valid at this time) thought he was back in Normal Law?

That to me is the chain of events that led to the stall with PF holding nose-up and THS moving to max due to those commands. The note is so vague on the fall, almost impossible to raise questions as of yet. My pet theory is the Captain got back in the LHS and took over the last minute but no real evidence except not sure senior PF would have given the stick over to junior PNF.

Thanks to any/all that can shed any light on what I see as the chain of events that all have to happen to lead to an accident of this nature.
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Old 7th Jul 2011, 03:09
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From page 13 post #260 - AF447 Thread No.3 and 2725 posts ago.
At 2 h 12 min 02, the PF said "I don’t have any more indications", and the PNF said "we have no valid indications". At that moment, the thrust levers were in the IDLE detent and the engines’ N1’s were at 55% the angle of attack decreased, the speeds became valid again and the stall warning sounded again.
My interpretation is that the aircraft was in a deep stall and passing through FL250 with RoD about 10,000 feet/min, and even though both engines N1's were 55%, the pitch-down inputs decreased the AoA and the airspeed data became valid. However, that IAS was low and the stall warning activated again but ceased with further pitch-up commands as the data again became invalid.

Without AoA information, neither pilot had any idea in what part of the stall regime they were, and seemed to react as if a return of the SW was indicating Vmo, hence the continuing pitch-up command. So failure at this time to persist with the pitch-down command effectively left them doomed, as even then with the time taken for the THS to readjust (if it was going to) and for the wings to start flying, meant that the chance of reducing the RoD to zero before FL0 was marginal.


It strikes me that no-one on the flight deck realized that the AoA data was only valid when IAS was greater than 60KTS. Even though they went looking for the FPV, it seems it was only after the SW stopped at 2:11:40 plus a few seconds, and therefore to no avail - see ACARS FPV messages timed 0212z. Their final chance to grab the FPV page was missed shortly after 2:12:02 when the stall warning sounded again - meaning valid airspeed!
Since the post above, A33Zab has provided information on the No Calculated Data (NCD) and PJ2 has provided a possible PFD image as a help to interpreting what the pilots were seeing at this time.

I have previously provided some updated timing for when the FPV page data was selected (between 02:11:55 and 02:11:59) and A33Zab has posited that the Capt ordered the thrust to idle. I also suspect that the Capt didn't know that the aircraft had been to FL380 and was in no better position than those in the front seats in understanding the reason for the SW following ND commands.

All were confused by the continuing NU eliminating the SW, and the PF most of all as he apparently didn't realize that the initial couple of stall warnings were short excursions into high AOA.

A system designed to provide warning of an approach to a stall has implemented that warning on the basis that the normal means of avoiding the stall will be taken. If as part of the design criteria an increasing AoA and decreasing IAS were further considered, then the NCD case would have resulted in "STALLED" in large red letters on the PFD.

Now stalling an Air Transport aircraft is what the SW set out to avoid, and the (NCD) lack of data on the PFDs resulted in the, "No valid indications" comment rather than, "We are stalled!"

If it is now possible to rationally explain some unforeseen bi-product of switching to ALT 2 LAW (following loss of airspeed data) that contributed to the "zoom climb" and inability of the crew to get the nose down, then all the A332 series aircraft could be at risk. I don't think that, and I guess that neither does Airbus Industries or the BEA. An aviation psychologist may provide an answer, but the simplistic approach is "action = reward", and that false reward needs to be addressed in the software logic associated with the Stall Warning.

I am not advocating that the FD crew become the servants of computers, though if those same computers had been programed to "save" the aircraft from the "crew", then IMHO none of what we are second guessing would have happened. The crew are given the right to have the final say, and sadly in this accident their interpretation of events turned out to be wrong.

EDIT :: It is worth noting that no control surface systems fault warnings entered the the CMC and resulted in ACARS messages. There was plenty of time for them to be transmitted, and due to the manner in which the BEA produced their Note, it may be safe to assume that there were no control faults recorded by the FDR.
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