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AF447 wreckage found

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AF447 wreckage found

Old 30th May 2011, 18:16
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I absolutely do not wish to start an Airbus v. Boeing thing - no interest in playing manufacturer top trumps at all.

However, I would be genuinely interested to know if and how this accident scenario might've been different - in terms of aircraft behaviour and what the pilots were presented with - if the aircraft involved had been one of Air France's 777s rather than one of their 330s?

Specifically in terms of autopilot/autothrust disconnection, stall warning being silenced <60KIAS, lack of AoA information, trim issues? Do you think the 777 would've been a more helpful/intuitive aircraft to grapple with in those desperate moments?

Again, not trying to stir it, just interested to know how much the aircraft type and design philosophy is to blame here (if at all) and if an alternative design might've helped those guys more...
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Old 30th May 2011, 18:27
  #1062 (permalink)  

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Didn't some Airbus fanatic write a book in which he said of Sullenberger's accident "It was the aeroplane that saved them. It cradled them all the way down to the river." Has he said anything about this accident?
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Old 30th May 2011, 18:32
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I'm a scientist, not a pilot.

It seems that the biggest source of uncertainty is what did the pilots know and what was their assessment of the situation.

There seems to be a lot of debate as to whether they were aware of or had reliable data about speed, pitch, aoa, etc. But, we know that they were aware of their altitude and rate of descent as they passed through 10,000 ft. Even so, they continued to pull back on the stick. Is it possible that they believed they were in a steep dive rather than a stall?

Is it possible to get a stall warning when pulling out of a dive?

Isn't a dive is more recoverable than a stall? With "no other indications" is it not possible to fool oneself into believing the more hopeful scenario?
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Old 30th May 2011, 18:43
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Originally Posted by Graybeard
I don't understand why the AP/AT had to drop out of Normal for flaky airspeed.
Because without that information, some of the protections can't work. Any protection out is an immediate drop to Alternate Law 2, which puts the pilots in near-absolute command of the control surfaces (any remaining protections can be overridden with sufficient control deflection).

It may surprise many, but it was part of the original specification for the systems that drive the A320 and her descendants that if, for whatever reason, the computers think they can't behave as they should, they defer to the pilots - on the understanding that they have more information available to them, especially in daylight when there's an external reference as to which way is up. The human brain can at least try to work with partial information to rationally attempt a solution to the problem at hand, whereas a computer can't.

Also, I think you may be getting the FCU (Flight control unit - i.e. the FBW part of the design) confused with the FMC (aka A/P and A/THR), which is much like that of a conventional airliner).

At least not in cruise. It could hold pitch and power for awhile without dropping out, giving the pilots time to analyze the situation without having to hand fly, too.
This would add unnecessary complexity to the system. In fact the A/P can be engaged again in Alternate Law, but with airspeed data out, it's not considered a good idea. I know I keep harping on about this, but if you look at the Birgenair 757 incident, you can see what happens when an autopilot tries to fly the aircraft with a blocked pitot tube (and that was on a calm night, with little or no convective activity for miles).

I've lost count of the number of times I've heard "Switch the damn computers out and give control back to the pilots", or words to that effect. That is *exactly* what happened in this case. Unfortunately, with no airspeed data over water in the middle of the night and threading their way through patches of very inclement weather, even the best and most experienced pilots can be overwhelmed.
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Old 30th May 2011, 18:45
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The main issue seems to be the uncertainty about the human factor, it appears. For that we'd need to hear the entire CVR contents to draw any conclusions. I'm quite sure there is a lot of stuff on there which would be immensely helpful, but which we are unaware of at this point.

FDR plots would be nice too, of course
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Old 30th May 2011, 18:58
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But, we know that they were aware of their altitude and rate of descent as they passed through 10,000 ft
Even so, they continued to pull back on the stick
We know ?
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Old 30th May 2011, 19:10
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No evidence of cb's?

"For the umpteenth time, there is no evidence the crew flew through a Cb. In fact, based on the last BEA report, the crew knew very well what was coming,weather-wise as they turned to avoid and briefed the cabin crew.

Had they then encountered mod or severe turb in the top of a Cb, I'm sure the BEA would have mentioned it."



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Old 30th May 2011, 19:13
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From pointers to drums... From dynamics to numbers...

ChristiaanJ: But the altimeter is a bad example, with the old "hours-minutes-seconds" clock scale (you know what I mean) not being all that fast and easy to read, and being implicated in several incidents (I don't remember accidents off-hand). Which is why the numerical 'drum' scale was added, even before we went to 'glass'.
The addition of the 'drum' scale to a single pointer was a good thing. But that is where the improvement should have stopped. Removal of the 'last' pointer completely degraded the 'altitude trend situational awareness'. Especially on a rough ride...

ChristiaanJ: Unfortunately, with the conversion to 'glass', just about all the moving pointers disappeared.
So, to close the circle again, for the removal of the 'trend situational awareness' the trend vector was 'invented'... euhh...? Which 'as such' is a nice additional feature to have... Not as a replacement...
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Old 30th May 2011, 19:14
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Danger Automation paralysis? Inexperience? Temporary Insanity?

At 2 h 10 min 51 , the stall warning was triggered again. The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs
The Flight Data Recorder recorded airspeed and altitude as displayed on the left primary flight display (PFD), and on the integrated standby instrument system (ISIS).

"There was an inconsistency between the speeds displayed on the left side and the integrated standby instrument system (ISIS). This lasted for less than one minute."

Even if the pilots were confused about momentary airspeed deviations and had no longer trusted the displayed airspeeds: It's a mystery as to why the Pilot Flying would pull back on the stick and climb from FL 350 to FL 380 during multiple stall warnings. Elementary, basic flying instinct learned from day one in flying school, should have made him do just the opposite. That is, to get the nose down, not up during a stall warning.

Curiously, the captain in the Colgan Air DH-8 crash in upstate New York had also pulled back on the yoke during the stall warning and active stick pusher...

Inexperienced pilot graduates from the same school...?
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Old 30th May 2011, 19:15
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To override the NU of the THS, in Alternate Law, one pulls back on the SS.

Yes? Was there confusion about the origin of the chronic NU on the way down?
I would assume so. To clear this, does one pull back to the stop and release?

"during" and "continuous" mean different things, yes?

If the cg was even partially ng, could the PF have confused the a/c insistence on climb with a 'stuck' "Law" command? One which he continually tried to 'Clear'? With intermittent full back ss to override??

see touch 'n oops below
Old 30th May 2011, 19:18
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nitpicker330 BACK TO THE BOOKS.

For someone who is "supposed" to know their aircraft, you really do spout a load...

Alternate 1
Alternate 2
What is that supposed to mean???

Don't you mean:
Alternate WITH protections
Alternate WITHOUT protections




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Old 30th May 2011, 19:26
  #1072 (permalink)  
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We know ?
We know almost nothing. So little data has been made public that making any assumptions and conclusions is quite premature, if not simply stupid. Nothing can be said for sure without going through the entire CVR transcript, while at the same time looking at the FDR data.

I have an unrelated question. One of the error messages transmitted by the aircraft was
Meaning: This message indicates that the TCAS is inoperative.
Is there any explanation why TCAS would fail? It seems completely unrelated to airspeed...
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Old 30th May 2011, 19:31
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@jcjeant - I'm just going by the bea rpt. The PF says "we're going to arrive at level one hundred." The report also says "the inputs made by the PF were mainly nose-up." It doesn't say that the last, simultaneous, inputs were nose down, so I assume they were nose up.

Still, my question is whether they might have thought they were in a dive?
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Old 30th May 2011, 19:31
  #1074 (permalink)  
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Is it possible to get a stall warning when pulling out of a dive?

It's called "high speed stall" or maybe "accelerated stall", and it occurs any time you're asking the wing to work beyond its max CL. The attitude of the aircraft is immaterial.

In fact, what we usually call a common stall (1.0 g) is a special case; in general a stall occurs whenever (mass x g) exceeds the wing's aerodynamic lifting capacity.
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Old 30th May 2011, 19:32
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There is some confusion among posters here, and in the press, about the flight path. The pitch attitude is reported to be around 15-16 degrees nose up, and the angle of attack to be 35-40 degrees. This translates to a flight path angle of -20 to -25 degrees. If the vertical speed is around 10,000 fpm (~100 knots), then the slant speed has to be the vertical speed divided by the sine of the descent angle, or somewhere around 250 knots. This is the true airspeed. The airplane was not fluttering down vertically like a leaf, and its forward speed was not 60 knots or 107 knots or whatever.
There is ample opportunity for confusion, since at different points in the report ground speed, AIS, and the erroneous speeds on the displays are mentioned. To understand what they are saying you have to keep the context of each separate in your mind.

As far as the forward speed, it was 107 knots when last recorded, according to the report. I assume that's GPS derived, so it should be accurate. However, that was ground speed, not the speed through the air. For your 250 knot estimate of airspeed to the true, that would imply a headwind speed of around 120 knots, which is unlikely. It was a thunderstorm, not a category 4 hurricane.

The report also mentions that the AOA in the final moments of the flight was always in excess of 35 degrees. It did not say how high it reached, nor what it was at the end of the recording. Thus, your assumption of only 40 degrees is probably an underestimate.

To put a perspective on it, if the wind was calm, then the actual flight path would be about 45 degrees down, AOA of about 61 degrees, with an actual speed through the air of about 151 knots.
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Old 30th May 2011, 19:43
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As for TCAS failing: might be completely unrelated to events. We sometimes have it momentarily failing in the CRZ and then rapidly coming back soon after.
However (speculation) it could be due to enormous amount of static (St Elmos) around the direction sensing receiving antenna etc.

In the grand scheme of things it's completely irrelevant to proceedings.

There but for the grace of God.
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Old 30th May 2011, 19:44
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ok you're in the cruise and the pitots ice up. airspeed/mach will stay at current values. Crew decides to reduce to turbulence speed., thrust reduces to achieve this. As actual a/c speed reduces autopilot starts to slowly pitch the nose up to maintain altitude and whilst doing so applies nose up trim. Maybe the thrust even reduced to idle at this point.

This continues until ths is at aft limit (remember the indicated speed/mach are still at original cruise values but the actual aircraft speed is much lower. Autopilot and autothrust disengage and a/c reverts to Direct law giving immediate pitch up due trim and a/c gains circa 3,000 ft and then enters dynamic stall. Presumably this zoom would give a slight reduction in static pressure, therefore the indicated speeds would increase.

The aspect that really interests me is that neither crew member noticed the increasing pitch attitude as the speed was reducing. What would the flight director be commanding throughout all this? If during the zoom upwards it's showing fly down to regain the selected flight level this might explain the initial side stick forward to regain.

If neither pilot wasn't paying any attention to the attitude then where were they looking?

Coming back to the issue of pitots getting iced up I still don't understand with modern design why this is a problem. There are plenty of other jet transports flying around the world where, as far as am aware, this has never happened. What is intrinsically different in the design of the system on this a/c?

Last edited by fireflybob; 30th May 2011 at 20:09.
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Old 30th May 2011, 19:44
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one of the things we learn in primary flight school is "hazardous attitudes". One of them is, iirc, "that can't happen to me". I read a lot of that one between the lines here. Scary.

I am fairly certain that either of the three pilots on board knew, at least in theory, how to recover from a stall.

btw: has anyone ruled out severe icing on the wings and stabilizers?
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Old 30th May 2011, 20:08
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Originally Posted by ap08
Is there any explanation why TCAS would fail? It seems completely unrelated to airspeed...
TCAS needs to know how fast they're going. If it doesn't it only has half the information (i.e. where they are) required to transmit .
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Old 30th May 2011, 20:10
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Flight Safety
Right Way Up, about as likely as 3 engines failing at the exact same time in the exact same way, not very likely.
Not sure why not as icing is likely to affect all pitots at the same time. With regard to engines failing its worth looking up the Miami- Nassau Tristar or the Royal flight 146!
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