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AF 447 Thread No. 5

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AF 447 Thread No. 5

Old 5th Aug 2011, 18:08
  #1621 (permalink)  
 
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Thanks for your comments.

The graphs I've posted were intended as complementary to the information and the points made by a set of my previous posts, as at the time, I didn't have the graphs available.

The goal of those posts was limited only to the explanation of the relationship between certain elements that are under pilot control, the Stall Warnings and the confusion in the cockpit.

I have not made any claims of completeness on the set of graphs, so it may be the case, that more graphs could be added for more information.

The reasons of WHY the STALL WARNING functioned the way it did was a NON-GOAL, was not in my intention to explain with those graphs, and post.

An analysis of WHY the STALL WARNING functioned the way it did, can be a topic for a different post, and set of graphs. Your suggestions are useful for such a set of graphs, and post.

I think, these clarifications should help with the use of the word "omit" as well.

Originally Posted by GarageYears View Post
airtren:

But you omit two key parameters from your graphs? Airspeed and AoA.... and since these two are fundamental to the generation of the Stall Warning itself I think you are painting a directed picture.

Take a look at the BEA data and it is clear that the Stall Warning basically follows CAS - the rest is coincidental to my eye at least.

Take just one Stall Warning occurrence - the one centered around 2.14.00 - on page 107 of the English version of the 3rd Report.... and exactly coinciding is a period where airspeed becomes greater than 60 knots. There is clearly some hysteresis around the airspeed value since short periods where CAS exceeds 60 knots don't trigger it, but when the value is there for a 'reasonable' period.

I suspect the problem is that excessive AoA leads to invalid CAS due to pitot characteristics - effectively the dynamic pressure is no longer being read since the inlet aperture is no longer 'inline' with the airflow, and the drain opening is exposed... all in all the problem is a vicious circle, driven by the insane AoA value.
I could add, that if a STALL is possible with the a/c in a recoverable situation, a reliable, and 100% working STALL WARNING mechanism would increase the chances for the recovery to succeed.

If we consider the causality chain, that the STALL is caused by a "lack of sufficient lift", which is caused by the range of the actual "airspeed" and/or "AoA", it may become clear that if we could sense, or measure directly "the lift", and thus the "lack of lift", then that would be perhaps an additional parameter, that would add to the reliability of the STALL detection/calculation mechanism.

Once IN THE STALL many of the systems necessary to understand the situation are compromised.

Solution = avoid STALLING
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Old 5th Aug 2011, 18:21
  #1622 (permalink)  
 
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If we consider the causality chain, that the STALL is caused by a "lack of sufficient lift", which is caused by the range of the actual "airspeed" and/or "AoA", it may become clear that if we could sense, or measure directly "the lift", and thus the "lack of lift", then that would be perhaps an additional parameter, that would add to the reliability of the STALL detection/calculation mechanism.
I respectfully disagree, and mostly in how you phrased that.

Lack of lift typically results in descent.

What happens at stall is the dramatic change in lift generation due to the disruption of airflow at a critical angle of attack.
Before that, lift and drag are generated in a particular manner.
Beyond that, the manner in which the airflow interacts with the airfoil changes. (More turbulent flow, less laminar ... etc)

If you know your AoA, and your critical AoA, then you know how close you are to a change you'd rather avoid.

To measure lift, just what frame of reference are you going to use?
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Old 5th Aug 2011, 18:22
  #1623 (permalink)  
 
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Originally Posted by takata View Post
Agreed 100%. I'll add that, beside being told to avoid stalling, pilots should be informed of what would eventually happen (as precisely as possible) to their systems if they missed the first part of the drill.
Agreed 100%.

I would go even further.

There should be an increased effort to help pilots understand the very basic laws of physics involved, in very simple, and practical terms.

That would make clear the very important causality chain, which forms a logical chain in the systems algorithms, which is not that different than the logic that one should apply mentally.

The training should be clear also about the limitations of the system, and how be able to detect when the system has reached its limitations, and how to use any other available indication for complementing the system and diagnosing the STALL.

"xcitation" mentioned, if I recall correctly, using a bottle of water for attitude indication..... great idea.... maybe add also an Emergency Kit, of very simple tools, which can function independent of anything else....
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Old 5th Aug 2011, 18:55
  #1624 (permalink)  
 
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Good call.
However how do you identify a real stall from a false stall?
How about, inter alia:

Higher than normal nose (pitch) attitude
+ High rate of descent

They could also have noticed that the sound of the airflow was indicative of low airspeed.

I thnk that PNF had the clues; what a shame he did not take control and act upon them.
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Old 5th Aug 2011, 19:11
  #1625 (permalink)  
 
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However how do you identify a real stall from a false stall?
By how the aircraft behaves, of course!

It's my sincerest hope that a professional "pilot" would never have to ask that question! I'm presuming those of you asking it are not pilots, because I can't imagine a pilot who could ever not know if he's stalled, PDQ, after the fact. The fact that recent years have shown us that those kind of pilots do exist - even while they earn their Darwin awards, ought to cause us all to have a really good look.... If any pilots reading here have any doubts, have no doubt that you DO need some training.
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Old 5th Aug 2011, 19:20
  #1626 (permalink)  
 
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Apologies if I mention things that were covered already.

(*I speculate*) Could the PF's initial response to pitch up have been to regain his original altitude of FL350? - Perhaps his altimeter showed a gradual loss in altitude as blockage occurred?

(as happened in previous events. See pg48 and pg51 of the following document: http://www.bea.aero/docspa/2009/f-cp090601e2.en/pdf/f-cp090601e2.en.pdf)

The PNF's action of switching the F/O displays to ADIRU 3 info seems to also suggest he felt ADR2 was less reliable.

Later on, after the captain is in the cockpit:

2 h 12 min 15 to 2 h 12 min 19
CAP: Là je sais pas là ça descends
There I don't know, there it's going down

His comments coincide with the AIR DATA and ATT-HDG selector being positioned to 'CAPT on 3'. Seems like a lot of confusion in the cockpit about what is happening with the altitude. The airplane is pitched nose-up, by this stage the PF claims to no longer have any V/S indication, and there continues to be doubt as to whether the airplane is gaining or losing altitude.


2 h 12 min 27
PNF: Tu montes ...
You're going up ...

PNF: Tu descends descends descends descends
go down go down go down go down

2 h 12 min 30
PF: Je suis en train de descendre là?
Am I going down?
(Pardon my French, but could the 'là' be the PF referring to PFD1 or the ISIS? As if to say "those instruments there say I'm descending???"

PNF: Descend !
Go down

2 h 12 min 32
CAP: Non tu montes là
No you're going up there
(WHERE does it show them climbing??? I am not so sure he is referring to pitch attitude)

2 h 12 min 33
PF: Là je monte okay alors on descend
There I'm going up ok so let's go down
(Once again - what is indicating to him that they are going up?)

There are only two things which I can think of which indicate up and down in an airplane (excluding the V/S indicator).
1) Pitch Attitude (in which case the whole discussion of up and down is in reference to attitude).
2)Altimeter information (in which case one of them is indicating an increase or constant altitude, while the other(s) indicate a decrease in altitude.

I am baffled by what could have been happening, and as the ADR2 data is not recorded by the FDR it leaves us wondering whether it was behaving in a similar fashion to ADR1 and 3, or doing something else. Otherwise...how could there be so much discussion about whether one is climbing or descending?!?

I strongly believe the captain's comment was in reference to this conflict of information:

2 h 12 min 44
CAP: (…) C’est pas possible
It's not possible

And I would be inclined to say the same - I don't think it's possible for one ADR to somehow be frozen or to be indicating an increase in altitude. Nor do I know whether it's possible for IR2 to be displaying different attitude information compared to IR1 and 3. But the entire talk of climbing/descending leads me to envision such scenarios.

As a final point - I do not doubt the experience or professionalism of the crew. I believe they did their best with the information that was presented to them, and I don't think it was as simple as the PF simply being 'behind the airplane' and not noticing where he was pointing the airplane - it's possible, but I imagine there's more pieces missing to this puzzle. Nor do I think he was chasing the intermittent FD bars. I think a pilot with his experience on the Airbus would know not to follow the FD bars blindly - it would serve no purpose in such a situation and I'm willing to bet he was aware of that.

PS - If it wasn't mentioned already, the airplane switched to Alternate 2 - meaning roll control was DIRECT. Maybe this contributed to his 'over controlling' in roll.
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Old 5th Aug 2011, 19:32
  #1627 (permalink)  
 
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DJ77 & Neptunus Rex

DJ77

Quite - hence my unease at the entire SS concept (#1535)


Neptunus Rex

Agreed re: PNF. If he had seen PF's control inputs between FLT350 and FLT380, he would have been there.....
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Old 5th Aug 2011, 19:39
  #1628 (permalink)  
 
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He did not need to see the control inputs...he could see the results.
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Old 5th Aug 2011, 19:44
  #1629 (permalink)  
 
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peefactor
3. But the entire talk of climbing/descending leads me to envision such scenarios.
The reaction on their inner ears should have told them that they were in a rapid descent. Plus, the Captain should have noticed the aircraft deck angle as he walked, or rather climbed, to the cockpit.

Airmanship again.
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Old 5th Aug 2011, 19:52
  #1630 (permalink)  
 
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Neptunus Rex

I am not talking objectively as to what should have happened/been triggered. I am talking subjectively as to what actually happened that particular night, based on what has been disclosed so far (shortly after his rest break, in the early hours). PNF was almost there, and just needed one or two more clues, and that is a separate question to what he should have needed under a proper training environment that properly equipped both pilots to deal with the situation they encountered (but then modern planes fly themselves and pilots are just a cost that reduces shareholder dividends, or so too many senior line management believe....).

Last edited by Welsh Wingman; 5th Aug 2011 at 20:12.
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Old 5th Aug 2011, 19:56
  #1631 (permalink)  
 
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Neptunus Rex,
How do you know which instruments are valid and which are bogus.
You might only have seconds to figure it out!

I recommend you read the QF72 interim factual 1, to see what the Quantus captain said. He was not certain of the "varacity" of all of them. Fortunately he had visual + good weather so the situation was less confusing than AF447.

QF72 interim factual 1, an extract.

The flight crew reported that the weather was fine and clear and there had been no
turbulence during the flight. At about 1239, the first officer left the flight deck for a
scheduled rest break. The second officer then occupied the right control seat.
At 1240:28, the autopilot disengaged. The crew reported that there was an
associated ECAM3 warning message (AUTO FLT AP OFF) and that they also
started receiving master caution chimes. The captain took manual control of the
aircraft using the sidestick. He reported that he attempted to engage autopilot 2 and
then autopilot 1, but neither action was successful.4 The flight data recorder (FDR)
showed that, during this period, the aircraft’s altitude increased to 37,200 ft before
returning to the assigned level.
The crew reported that they cleared the AUTO FLT message from the ECAM. They
then received a NAV IR1 FAULT message on the ECAM.5 The crew were also
receiving aural stall warning indications at this time, and the airspeed and altitude
indications on the captain’s primary flight display (PFD) were also fluctuating.
Given the situation, the captain asked the second officer to call the first officer back
to the flight deck.
At 1242:27, while the second officer was using the cabin interphone to ask a flight
attendant to send the first officer back to the flight deck, the aircraft abruptly
pitched nose-down. The captain reported that he applied back pressure on his
sidestick to arrest the pitch-down movement. He said that initially this action
seemed to have no effect, but then the aircraft responded to his control input and he
commenced recovery to the assigned altitude. The aircraft reached a maximum
pitch angle of about 8.4 degrees nose-down during the event, and a maximum g
loading of -0.80 g6 was recorded. The aircraft descended 650 ft during the event.
The flight crew described the pitch-down movement as very abrupt, but smooth. It
did not have the characteristics of a typical turbulence-related event and the
aircraft’s movement was solely in the pitching plane. They did not detect any
movement in the rolling plane.
During the initial upset event, the second officer activated the seatbelt sign to ON
and made a public address for passengers and crew to return to their seats and
fasten their seatbelts immediately.
The flight crew reported that, after returning the aircraft to 37,000 ft, they
commenced actions to deal with multiple ECAM messages. They completed the
required action to deal with the first message (NAV IR1 FAULT) by switching the
captain’s ATT HDG (attitude heading) switch from the NORM position to CAPT
ON 3 position, and then cleared that message. The next message was PRIM 3
FAULT.7 The crew completed the required action by selecting the PRIM 3 off,
waiting 5 seconds and then selecting it on again.
At 1245:08, shortly after the crew selected PRIM 3 back on, the aircraft
commenced a second uncommanded pitch-down event. The captain reported that he
again applied back pressure on his sidestick to arrest the pitch-down movement. He
said that, consistent with the first event, that action was initially unsuccessful, but
the aircraft then responded normally and he commenced recovery to the assigned
altitude. The aircraft reached a maximum pitch angle of about 3.5 degrees nosedown,
and descended about 400 ft during the second event. The flight crew
described the event as being similar in nature to the first event, though of a lesser
magnitude and intensity.
The captain announced to the cabin for passengers and crew to remain seated with
seatbelts fastened. The second officer made another call on the cabin interphone to
get the first officer back to the flight deck. The first officer returned to the flight
deck at 1248 and took over from the second officer in the right control seat. The
second officer moved to the third occupant seat.
After discussing the situation, the crew decided that they needed to land the aircraft
as soon as possible. They were not confident that further pitch-down events would
not occur. They were also aware that there had been some injuries in the cabin, but
at that stage they were not aware of the extent of the injuries. At 1249, the crew
made a PAN8 emergency broadcast to air traffic control, advising that they had
experienced ‘flight control computer problems’ and that some people had been
injured. They requested a clearance to divert to and track direct to Learmonth, WA.9
Clearance to divert and commence descent was received from air traffic control.
Figure 1 shows the track of the aircraft and time of key events.

Following the second upset event, the crew continued to review the ECAM
messages and other flight deck indications. The IR1 FAULT light and the PRIM 3
FAULT light on the overhead panel were illuminated. There were no other fault
lights illuminated. Messages associated with these faults were again displayed on
the ECAM, along with several other messages. The crew reported that the messages
were constantly scrolling, and they could not effectively interact with the ECAM to
action and/or clear the messages. The crew reported that master caution chimes
associated with the messages were regularly occurring, and they continued to
receive aural stall warnings.
The captain reported that, following the first upset event, he was using the standby
flight instruments and the first officer’s primary flight display (PFD, see Appendix
A) because the speed and altitude indications on his PFD were fluctuating and he
was unsure of the veracity of the other displayed information. After the second
upset event, he had observed that the automatic elevator trim was not functioning
and he had begun trimming the aircraft manually. He later disconnected the
autothrust and flew the aircraft manually for the remainder of the flight.
The flight crew spoke to a flight attendant by interphone to get further information
on the extent of the injuries. The flight crew advised the cabin crew that, due to the
nature of the situation, they did not want them to get out of their seats, but to use the
cabin interphones to gather the information. At 1254, after receiving advice from
the cabin of several serious injuries, the crew declared a MAYDAY10 and advised
air traffic control they had multiple injures on board, including a broken leg and
some cases of severe lacerations.
The crew continued attempts to further evaluate their situation and, at 1256,
contacted the operator’s maintenance watch unit11, located in Sydney, by
SATPHONE to seek assistance. There were several subsequent communications
during the flight between the flight crew and maintenance watch, who advised that
the various faults reported by the crew were confirmed by data link, but that they
were not able to diagnose reasons for the faults. During one of the conversations,
maintenance watch suggested that the crew could consider switching PRIM 3 off,
and this action was carried out. This action did not appear to have any effect on the
scrolling ECAM messages, or the erratic airspeed and altitude information.
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Old 5th Aug 2011, 19:56
  #1632 (permalink)  
 
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It has been said before but I d like to add my voice to this opinion. English is a much more factual language then French.

The French language is in my humble opinion too ambivalent to be used in a factual environment like a cockpit in distress.

Là is such a word which could be used in the sense of indicating a position (there) or a given time (then), and there are more.

Perhaps there has been no misunderstanding between pilots on the deck about the intentions of whoever spoke in this specific case. I do not feel qualified to judge this, despite having been raised in part in French, but others should.

I realize some French natives may object to my humble opinion, French are notoriously protective of their language, as it is a fundamental part of their cultural heritage (just think of the French laws requiring French broadcasting stations to broadcast a certain % of music in French), but I do think the discussion should be had.

Time for a quick exit....
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Old 5th Aug 2011, 20:11
  #1633 (permalink)  
 
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xcitation (QF72)
The crew reported that master caution chimes associated with the messages were regularly occurring, and they continued to receive aural stall warnings.
If the conventional wisdom among A330 pilots, or some A330 pilots, was that with UAS/Pitot problems, stall warning is generally spurious ... that might explain the reaction to stall warnings not being what we'd expect.

The cry of "wolf," or the cricket chirp of "wolf" could be a case here.
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Old 5th Aug 2011, 20:14
  #1634 (permalink)  
 
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Lonewolf 50

Definitely a cricket chirp
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Old 5th Aug 2011, 20:49
  #1635 (permalink)  
 
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3hole...
By how the aircraft behaves, of course!

It's my sincerest hope that a professional "pilot" would never have to ask that question! I'm presuming those of you asking it are not pilots, because I can't imagine a pilot who could ever not know if he's stalled, PDQ, after the fact. The fact that recent years have shown us that those kind of pilots do exist - even while they earn their Darwin awards, ought to cause us all to have a really good look.... If any pilots reading here have any doubts, have no doubt that you DO need some training.
We do not all have your "Chuck Yeager" skill level. The rest of us non-aces require extensive training.

This was a stall in an a/c with degraded instruments, ALT LAW, no visual in chop. Not a trivial case. The inexperienced PF did try stick forward however a/c still stays nose up no response, as elevator is at -30 deg due to full THS! So behaviour is bizarre and only explained if you have a full understanding of the situation in 60 seconds. Even then you would be faced with stall recovery - also not trained for and not trivial.

Bus pilots have stated that ALT LAW behaves like no other a/c you have flown! So if you have not tried it don't you think it is a bit presumptive/over simplistic to "see how a/c behaves".

Even the QF72 CAP with the help of experience, day time, normal law, good weather still doubted varacity of all his instruments. Fortunately he could correctly ignore his stall warnings. IMHO given the details of AF447 incident it was a difficult and exceptional situation.
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Old 5th Aug 2011, 20:50
  #1636 (permalink)  
 
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Originally Posted by takata
It seemed normal to me and no, BEA would not comment something "normal" without good reasons to do so.
I'm afraid, takata, you will have to explain me what's "normal" in it ... ?
I am very curious of that kind of normality.

BTW, is the AoA1 value stuck at 2.1 deg part of the normality too ?



Following, something I'm not sure to understand - How things work - What's the logic behind ?
Maybe A33Zab could explain ... Thanks.

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Old 5th Aug 2011, 20:51
  #1637 (permalink)  
 
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Back up instruments - not inadequate training

As an electronic engineer and pilot of 50 hours, before a pacemaker intervened, I an astonished that all the blame is being put on the pilots and “lack of training”. The cause of the accident is absolutely plain. The automatic systems and glass cockpit completely failed the pilots by providing erroneous and variable indications. With a carefully designed back-up of dependable instruments such as gyros and inertial navigators, and others, pilots would not be without believable data. When the automatics fail catastrophically, as in this case, they should be cut out. The so called stall would never have been believed and subsequently would not have been turned into a real stall. The fault lies with (ALL) modern aircraft design.
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Old 5th Aug 2011, 20:56
  #1638 (permalink)  
 
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Lonewolf

I've expressed an idea, in a quick post ... and you're nit picking on that.
giving me the opportunity to muse on semantics....

I could say that I disagree with you, based on how you describe the "descent" as being caused by a "lack of lift".

I could say, a "descent" is caused by "a gradual diminishing of lift" not a "lack of lift".

"Lack of lift", means (to me) "absence of lift". and thus "fall".
You called it "drastic change in lift".... well, yeah,.... it is a change that results in "lack of lift"....

But we can also say that "fall", is a "descent", with the qualifier "at high or very high vertical speed".... . That's BEA's language?

So, we can say, that the "stall/lack of lift" is a subset of the larger set which is "change of lift", which includes the other subset, which is the normal "descent/gradual change of lift".

For that AoA, isn't that bottle of water that "xcitation" mentioned a genial idea????

Originally Posted by Lonewolf_50 View Post
I respectfully disagree, and mostly in how you phrased that.

Lack of lift typically results in descent.

What happens at stall is the dramatic change in lift generation due to the disruption of airflow at a critical angle of attack.
Before that, lift and drag are generated in a particular manner.
Beyond that, the manner in which the airflow interacts with the airfoil changes. (More turbulent flow, less laminar ... etc)

If you know your AoA, and your critical AoA, then you know how close you are to a change you'd rather avoid.

To measure lift, just what frame of reference are you going to use?

Last edited by airtren; 5th Aug 2011 at 22:51.
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Old 5th Aug 2011, 21:01
  #1639 (permalink)  
 
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@xcitation
Worry not, sir. I'm no Chuck Yeager. I don't even fly any more. But I'm certain that a stalled aircraft behaves just like a stalled aircraft, and ALL pilots should know that behaviour. In this case you can clearly see in the traces the A/C was indeed behaving just like a stalled aircraft. Keep on training!
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Old 5th Aug 2011, 21:11
  #1640 (permalink)  
 
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Originally Posted by vanHorck View Post
It has been said before but I d like to add my voice to this opinion. English is a much more factual language than French.
I totally agree with your remarks.... French is NOT a technical language.
Speaking as another Dutchman, who's spent half his life in France (aircraft industry), but with English as the 'family' language at the same time (long story, and not really 'on topic' here).
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