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AF 447 Thread no. 4

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AF 447 Thread no. 4

Old 16th Jun 2011, 03:12
  #21 (permalink)  
 
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Originally Posted by GB
From the above, it seems fuel transfer to the tail is automatic once in cruise. There is no mention in the BEA info that fuel was manually transferred forward, so how did the CG get to 29% in latest BEA note, from 37% in initial reporting?
37% CG would be a big difference from 29% in manual pitch control. It's real easy to over control with aft CG.
The initial estimate of 37% was probably erroneous :
http://www.pprune.org/tech-log/45283...ml#post6484163


Originally Posted by DozyWannabe
I oversimplified the description
You did not oversimplify anything, you make up technical stuff on your own and obviously not able to back up by the appropriate Operation Manual reference when requested.
"The only way autotrim is activated is if the stick is fully deflected and held there past the elevator travel limit"
Give me your reference that I learn something … or retract it !

If it’s getting personal or insulting to challenge what appears to be unfounded statements, so I am.

And if you want us to discuss Habsheim, start a thread on its own, or stop making redundant innuendo.
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Old 16th Jun 2011, 03:44
  #22 (permalink)  
 
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So many questions about stalls

More:
1. Why did the pitots ice up?
2. Why did the A/P and A/T disconnect?
3. Why the zoom climb without clearance from ATC?
4. Why the sudden reduction of speed at top of climb?
5. Why when at the same time the plane went into the thunderstorm?

Any connection?

The unanimous comment from my group of old retired pro's: Why didn't they deviate?

Comment: When an airplane comes out at the top of an uncommanded zoom climb almost 3000 feet above their max altitude below 60 kts, it is out of control! The flight controls do not have ANY effect. As we have seen until it hit the bottom.

Thunderstorms are known to contain strong up and down drafts. For 50 years we in the pilot community have been warned to avoid, avoid, avoid them.
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Old 16th Jun 2011, 04:38
  #23 (permalink)  
 
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Thunderstorm do's and don'ts

full text of the classic FAA guide


DO'S AND DON'TS OF THUNDERSTORM FLYING

Above all, remember this: never regard any thunderstorm as “light” even when radar observers report the echoes are of light intensity. Avoiding thunderstorms is the best policy. Following are some Do's and Don'ts of thunderstorm avoidance:
  1. Don't land or take off in the face of an approaching thunderstorm. A sudden wind shift or low level turbulence could cause loss of control.
  2. Don't attempt to fly under a thunderstorm even if you can see through to the other side. Turbulence under the storm could be disastrous.
  3. Don't try to circumnavigate thunderstorms covering 6/10 of an area or more either visually or by airborne radar.
  4. Don't fly without airborne radar into a cloud mass containing scattered embedded thunderstorms. Scattered thunderstorms not embedded usually can be visually circumnavigated.</I>
  5. Do avoid by at least 20 miles any thunderstorm identified as severe or giving an intense radar echo. This is especially true under the anvil of a large cumulonimbus.
  6. Do clear the top of a known or suspected severe thunderstorm by at least 1,000 feet altitude for each 10 knots of wind speed at the cloud top. This would exceed the altitude capability of most aircraft.
  7. Do remember that vivid and frequent lightning indicates a severe thunderstorm.
  8. Do regard as severe any thunderstorm with tops 35,000 feet or higher whether the top is visually sighted or determined by radar.
If you cannot avoid penetrating a thunderstorm, following are some Do's Before entering the storm:
  1. Tighten your safety belt, put on your shoulder harness if you have one, and secure all loose objects.
  2. Plan your course to take you through the storm in a minimum time and hold it.
  3. To avoid the most critical icing, establish a penetration altitude below the freezing level or above the level of —15° C.
  4. Turn on pitot heat and carburetor or jet inlet heat. Icing can be rapid at any altitude and cause almost instantaneous power failure or loss of airspeed indication.
  5. Establish power settings for reduced turbulence penetration airspeed recommended in your aircraft manual. Reduced airspeed lessens the structural stresses on the aircraft.
  6. Turn up cockpit lights to highest intensity to lessen danger of temporary blindness from lightning.
  7. If using automatic pilot, disengage altitude hold mode and speed hold mode. The automatic altitude and speed controls will increase maneuvers of the aircraft thus increasing structural stresses.
  8. If using airborne radar, tilt your antenna up and down occasionally. Tilting it up may detect a hail shaft that will reach a point on your course by the time you do. Tilting it down may detect a growing thunderstorm cell that may reach your altitude.
Following are some Do's and Don'ts During thunderstorm penetration:
  1. Do keep your eyes on your instruments. Looking outside the cockpit can increase danger of temporary blindness from lightning.
  2. Don't change power settings; maintain settings for reduced airspeed.
  3. Do maintain a constant attitude; let the aircraft “ride the waves.” Maneuvers in trying to maintain constant altitude increase stresses on the aircraft.
  4. Don't turn back once you are in the thunderstorm. A straight course through the storm most likely will get you out of the hazards most quickly. In addition, turning maneuvers increase stresses on the aircraft.

Table of Contents
Previous Section: Thunderstorms and Radar
Next Section: Common IFR Producers
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Old 16th Jun 2011, 07:28
  #24 (permalink)  
 
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Direct (K.I.S.S.*) questions

Hi,

1. Why did the Pitots ice up?
Because the a/c flew into a region with certain characteristics, equipped with 3 identical Air Speed sensors (Pitot tubes) not adequate for this "region". These sensors (Thales) presented some anomalies before (in other flights) and were scheduled to be replaced by BF Goodrich ones. The accident occurred before the change in the F-GZCP plane.

2. Why did the A/P and A/T disconnect?
Because the Airbus SAS System requires reliable information from the sensors in order to work at full specifications. When entering (a region with certain characteristics) and the sensors start to present anomalies, the System change the a/c operation mode (LAW) disconnecting A/P and A/T, etc. We don´t yet have information on other (possibly) occurred sensor anomalies that could also lead to this "disconnection" (due mode change, LAW).

3. Why the zoom climb without clearance from ATC?
In this region they were capable to use HF and Data comm. They tried to use Data comm with DKR ACC for 3 times, some minutes before. During the sudden zoom climb they certainly were not able to even think on comm for FL change.

4. Why the sudden reduction of speed at top of climb?
The a/c changed speed by altitude and with THS "going" to 13° UP with/and NU commands, she eventually stalled. And they were facing non reliable air speed in their displays and also in the ISIS (3rd and redundant resource). So the real speed (during many moments) after icing up nobody will ever know. Just estimate, based at other data, (risky estimate). The info was just lost (simply not measured, due "sub heated sensors" ).

5. Why when at the same time the plane went into the thunderstorm?
The decision making to go straight (and not deviate) was made before. "Inside" the WX they started a 12° LH deviation, then the zoom climb started. We don´t have the CVR info to understand on the "decision" to go in the straight route. Other planes deviated. On this particular aspect see BEA reports and Tim Vasquez

below 60 kts, it is out of control!
Nobody has the "real" speeds during many moments during this phase. The sensors were just not working properly. The FDR will show us the moments when the speeds were correctly measured. (Again, the a/c was equipped with air speed sensors not compatible to the region she entered)

The flight controls do not have ANY effect.
The (very little) information BEA released on that suggest they had "some control".

Thunderstorms are known to contain strong up and down drafts. For 50 years we in the pilot community have been warned to avoid, avoid, avoid them.
Several cases of Unreliable Air Speed occurred during deviations from WX.


(*) KISS principle - Wikipedia, the free encyclopedia


Why didn't they deviate?
CVR certainly will help us to understand why.
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Old 16th Jun 2011, 07:33
  #25 (permalink)  
 
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So I asked myself: how does one recover from a stall without reliable airspeed and without AoA?
This is simple stuff, you use your remaining instruments and return to basics: use pitch and power. And you certainly do not continue pulling.
I would think that the proper action would be a determined nose-down push, maintained until the stall warning stops, and then trying to maintain an AoA on the edge of s/w, gently allowing the nose to raise until s/w occurs, then a small nose-down correction to silence it, etc., until back in approximately level flight at a reasonable pitch attitude.
Scary stuff,. You don't use the stall warning to calibrate your response, you use your remaining instruments and your knowledge of your aircrafts pitch/power settings. Your solution puts you at an unnacceptable risk of secondary stall and that is another opportunity to enter a spin. If you do not know your aircraft's pitch/power settings for level flight then you are not competent to pilot it/manage its autopilot and take over if/when that autopilot fails.
EDIT:: Can anyone be expected to do that succesfully without being trained for that eventuality?
Of course not, you are not born with the ability to recover from unusual attitudes using partial panel. You learn this when you take your instrument rating. If you have lost your scan you are not competent to fly in clouds.

It really is that simple.

I'm struck by the fact these guys managed to "fly" and reverse course at what is essentially under minimum controllable airspeed, for five minutes, in turbulence, and they hit the water belly side down and reasonably flat. That is a huge credit to the designers of the airframe, must be inherently incredibly stable.
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Old 16th Jun 2011, 07:41
  #26 (permalink)  
 
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@RetiredF4: As I mentioned previously, an aerofoil doesn't cease to be an aerofoil and stop producing lift just because it's at high AoA and stalled. Yes, it produces a lot of drag (component of force parallel to the airflow) as your barndoor would, but there is still significant lift (component of force normal to the airflow). Since you don't want to just take my word for it (fair enough), here's a link to a study specifically of post-stall aerofoil behaviour; it has a good set of Cl/Cd/Cm-alpha graphs going up to extremely high AoA. You'll notice that the motivation for this study wasn't aircraft behaviour, but wind turbines; there's been a lot of interest in post-stall aerofoil chracteristics because they spend quite a bit of their time operating in a stalled condition!
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Old 16th Jun 2011, 08:04
  #27 (permalink)  
 
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That is a huge credit to the designers of the airframe, must be inherently incredibly stable.
Attitude stable yes - pity it was not speed stable.
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Old 16th Jun 2011, 08:12
  #28 (permalink)  
 
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Stability

Hi,

That is a huge credit to the designers of the airframe, must be inherently incredibly stable.
And Airbus SAS learned something not "testable" before. The airframe designers received (from the FDR) an important information.

And now are being able to learn other very important "things" on the a/c.
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Old 16th Jun 2011, 10:53
  #29 (permalink)  
 
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That is a huge credit to the designers of the airframe, must be inherently incredibly stable.
Stability in a downward 'mush' is no advantage unless you have the power or pitch authority to then accelerate back into normal flight. Indeed, if the aircraft had rolled over to 90 degrees through instability, possibly aided by some agressive rudder input then may that have allowed a recovery?
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Old 16th Jun 2011, 11:19
  #30 (permalink)  
 
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OUCH!!

OUCH, previous poster.

Agressive rudder input in a transport category airplane? No thank you, has been tried before (New York, nov 2001), wasn't an overwhelming succes.

Why not just push the stick forward, instead of full aft, would most probably work like a charm. Forward trim might be used as well, to make life easier.

Unreliable airspeed, alright, but there never was any unreliability in the ATTITUDE: four independant sources available (IRS 1, 2, 3 and ISIS attitude).

When ever, in a big lumbering airliner, is 15 degrees pitch up an appropriate ATTITUDE? Only after lift-off, with take-off thrust set on all engines. NEVER around FL350.
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Old 16th Jun 2011, 11:34
  #31 (permalink)  
 
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@CONF - I have never "made stuff up" on this subject in my life, and I always make a point of checking what I'm saying beforehand - with others if possible, some of whom are pilots. My knowledge is strictly engineering and systems design.

So I oversimplified and rendered the information badly - that said, I've still yet to see any proof that an "inadvertent" pull back on the stick would command a nose-up so aggressive that 13 degrees of THS up-trim is required for full elevator authority, or proof that neutral stick would do the same - Chris's theory notwithstanding (for which there seems to be some debate about which speed neutral stick switches from "G-load" command to "Zero Pitch"). I think the only way we'll know for sure is when the BEA release the interim report. Only problem there is that there are those on here, yourself included, that will never believe anything the BEA says regarding an Airbus aircraft - so I fear that these arguments will go on and on and on...

Last edited by DozyWannabe; 16th Jun 2011 at 17:27.
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Old 16th Jun 2011, 11:35
  #32 (permalink)  
 
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EMIT

My post / question was based on the theory (admittedly unproven) that there was insufficent pitch authority to escape from this situation.

I just don't buy the idea that they were scared away from their one attempt at corrective pitch action by the restart of the stall warning and consequently maintained pitch up inputs for the remaining two minutes plus. The BEA report leaves large gaps but surely they must have tried everything?
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Old 16th Jun 2011, 12:01
  #33 (permalink)  
 
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AF 447 Elevator trim

Is there a determination of how the elevator trim came to be so high, nose up? The trim has more authority than the elevator and I doubt it is possible to recover from a deep stall with the trim full, or nearly full, in the nose up condition. My reading of the Airbus control laws is that automatic pitch trim is "available" in the Alternate Law mode. Did the trim go to the nose up position from pilot input or is there some envelope protection or other reason for it?

In the jet upset cases, it is hypothesized, that an updraft or headwind increase from penetrating an upper frontal boundary caused the aircraft to pitch up; the pilot pushed over but also trimmed nose down then the aircraft developed a steep descent with the pilot pulling hard to resist; the elevator force was sufficient to jam the elevator trim jackscrew so nose up trim could not be accomplished; the aircraft developed a steep dive which could not be corrected. Is it possible in this case, the pilots were attempting to cause a nose down condition and the elevator force was sufficient to jam the elevator trim?

There is a dynamic stall condition, discussed by S.S. Horner in his book on Fluid Dynamics where the AOA at which airflow re-attaches to the upper surface of the wing is significantly less than the AOA at initial stall.
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Old 16th Jun 2011, 12:15
  #34 (permalink)  
 
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wmelvin and several recent posters: Please read the thread, particularly Part 3 (found here> http://www.pprune.org/tech-log/45283...ad-no-3-a.html). I believe every aspect of your question(s) have been examined, discussed, re-examined and turned inside out through the course of those posts. Re-hashing those same discussions will not further our understanding unless new information comes along with such posts. I don't mean to be dismissive, but many here have been with this thread since the initiating event and I am sure you will find an enormous amount of info (along with a lot of dross, it is true) in the tens or hundreds of pages that make up the body of work here.
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Old 16th Jun 2011, 12:16
  #35 (permalink)  
 
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@wmelvin

Time-consuming as it may be, I recommend you read the earlier thread(s) - a lot of your questions will be if not answered, at least debated there.
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Old 16th Jun 2011, 13:28
  #36 (permalink)  
 
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THS post stall lift

HeavyMetallist

@RetiredF4: As I mentioned previously, an aerofoil doesn't cease to be an aerofoil and stop producing lift just because it's at high AoA and stalled. Yes, it produces a lot of drag (component of force parallel to the airflow) as your barndoor would, but there is still significant lift (component of force normal to the airflow). Since you don't want to just take my word for it (fair enough), here's a link to a study specifically of post-stall aerofoil behaviour; it has a good set of Cl/Cd/Cm-alpha graphs going up to extremely high AoA. You'll notice that the motivation for this study wasn't aircraft behaviour, but wind turbines; there's been a lot of interest in post-stall aerofoil chracteristics because they spend quite a bit of their time operating in a stalled condition!
Good reference, with witch i was familiar already. But i´m unable to see how you would prove your point of enough THS authority being available at 60° AOA.

Lets start on page 153 of your reference with the lower graph, which shows how drag is a function of AOA. The more AOA, the higher the drag. To reduce drag, you have to reduce the AOA.

Now lets look at the upper table, Coefficient of lift versus AOA. Lift increases with AOA, until stall AOA is reached. In that graph that is at about 20°AOA. This drop in Lift continues till 30° AOA. From a max CL of 1.4 at 20°AOA CL has dropped to CL 0.9 at 30° AOA. If we continue to increase the AOA to 45°AOA, CL would increase to 1.2 again. But remember and check the lower graph, we just have increased the CD by the factor of six from stallspeed until 45° AOA. ! If we increase the AOA above 45° to 60° AOA, CL decreases again and CD continues to increase.

What does it tell for the A330?
First of all i dont know what kind of profile the THS represents, but your reference shows, that most mentioned airfoils have a similar behavior, just the numbers change. So lets use what we got until someone comes up with the correct profile.

Lets start with the 46.5°AOA of the THS (60° Aircraft AOA minus 13.5° NU trim) , which gives us a CL of 1.2 and a CD of 1.2. Lets do some ND input by trimming the THS to 0° and let´s see what it does to our numbers. We end up at 60° AOA at the THS, a CL of 1.0 and a CD of 1.6! Our upforce on the THS needed for lowering the nose has decreased and the drag has increased, our ND trim has caused the opposite of our desired outcome.

But that´s not all, lets start again at 47.5° AOA with CL1.2 and CD 1.2 and let us pull full aft stick. That decreases the AOA of the THS for example to 30°AOA, but at the same time we are loosing CL to 0.9, (loosing upforce on the THS again) but we improve CD to 0.5.

Conclusion in this simulated case with this airfoil: Somehow you are stuck between max CL pre-stall and max CL post stall and the airfoil itself has no authority to change that.

To make matters worse, the same applies to the other airfoil, the wings. There´s probably a similar change in CL and CD and any positive change on the THS (somehow generating ND force for the aircraft) might bring the AOA of the wing into the region, where the decrease of AOA initially causes an increase of CL thus rendering your success on the tail usesless for the complete fuselage.

As mentioned before, i´m no aerodynamics guy and might be completely wrong, but i like to make the point that the crew most probably had no conventional way to get AF447 out of a 60°AOA stall and that their behavior described by the BEA in the last 3 minutes of the fall might reflect the helpless situation they found themselves in due to normal aerodynamic layout and behavior of the aircraft, which has never been tested in that flight region.

Another point to remember: That THS has never been designed and tested to generate negative g or great nose down pitching momentum (like in a fighter aircraft), but to keep the nose up in cruise and especially during approach to land.

Another point: CG might have travelled aft (some fuel in the tanks not equally distributed, but now in the aft parts of the tanks, Some cargo in the belly falling to the rear part of the hold, and shift of the center of lift due to high AOA, a mixture which ruins your day.

Last edited by RetiredF4; 18th Jun 2011 at 10:59.
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Old 16th Jun 2011, 13:48
  #37 (permalink)  
 
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Quote from HazelNuts39 (Jun15/1433z):
So I asked myself: how does one recover from a stall without reliable airspeed and without AoA? I would think that the proper action would be a determined nose-down push, maintained until the stall warning stops, and then trying to maintain an AoA on the edge of s/w, gently allowing the nose to raise until s/w occurs, then a small nose-down correction to silence it, etc., until back in approximately level flight at a reasonable pitch attitude.
EDIT:: Can anyone be expected to do that succesfully without being trained for that eventuality?

Quote from PA_18_151 (Jun16/0733z):
Scary stuff,. You don't use the stall warning to calibrate your response, you use your remaining instruments and your knowledge of your aircrafts pitch/power settings. Your solution puts you at an unnacceptable risk of secondary stall and that is another opportunity to enter a spin. If you do not know your aircraft's pitch/power settings for level flight then you are not competent to pilot it/manage its autopilot and take over if/when that autopilot fails.

Think you are missing HN39's point.

This aeroplane should not have stalled. It should not have zoom-climbed 3000ft, trading kinetic energy for potential energy ("speed for height"). But, for whatever reason, it did. Your advice like that buried in a badly-written QRH procedure, and discussed on these threads for over two years is spot-on prior to the climb from FL350, and might even have sufficed passing FL375 (AoA +4). Very soon after that, however, the wing stalled, and the AoA started rising rapidly. From then, the PF (perhaps unknowingly, although he did select TOGA thrust) was faced with a very different problem, which is the one that HN39 is addressing. (By the way, TOGA is little more than CLB thrust at high altitude.)

So the aeroplane is already in the stall (becoming a deep one). FPA display has been lost, and with it any chance of obtaining a rough idea of AoA. The VSI is soon off-scale (down), and it's night IMC. I assume you agree with HN39 that "the proper action would be a determined nose-down push", but that this should be sustained until well after the stall warning stops. Yes, there's a great risk of a secondary stall during the flare. But, with no reliable source of IAS, do you risk over-speeding the aircraft or and/or hitting the sea? If you end up very fast, how much height would be lost from an FPA of, say, -30deg**, at the 2.5G limit? With the altimeter racing downwards in a way you've never experienced except during a simulator "reset", at what point do you start pulling?

** (assuming stall recovery was started at, or soon after, the apogee)
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Old 16th Jun 2011, 14:01
  #38 (permalink)  
 
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Retired F4, 35
As mentioned before, i´m no aerodynamics guy and might be completely
wrong, but i like to make the point that the crew most probably had no
conventional way to get AF447 out of a 60°AOA stall and that their
behavior described by the BEA in the last 3 minutes of the fall might
reflect the helpless situation they found themselves in due to normal
aerodynamic layout and behavior of the aircraft, which has never been
tested in that flight region.
This is way I see it as well and mentioned in a previous post. If the
a/c has never been tested in such a situation, how can the crew be
expected to recover ?.

Testing the water here, but is that an argument for a tail chute to be
fitted to civil transports, or is that too far off the wall and would
it add to problems in that it might cause structural damage to the
airframe ?.

Another thing that's been nagging me about the last bea report is that
when the ap and ath disengaged, there was a "roll to the right". This
strikes me as odd as one would expect that at the point of disengagement,
they should hand back without change of ap or ath settings. Thus,
no immediate change. Why the uncommanded roll to the right, systems
fault, or what ?...
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Old 16th Jun 2011, 15:41
  #39 (permalink)  
 
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LG´s, drag chutes, etc

Hi,

Testing the water here, but is that an argument for a tail chute to be
fitted to civil transports, or is that too far off the wall?
Considering the fact "prevention" can fail what kind of resource could be used to "remedy"?

Unfortunately the "bean counters", ROI considerations are against us, technicians.

and would it add to problems in that it might cause structural damage to the airframe ?.
It would be better "written off" a/c´s than other similar tragedies.

If even for "sub heated Pitot´s" we have long delays for "fixing" one could easily imagine what will happen for airliners "stall recovery resource(s)". Probably no chances and probably there are better approaches to the issue. Like the ASAP introduction of "real redundant" air speed sensors. So, Airbus SAS seems to be working on that important issue, vital (AF447 is showing this) for their "advanced planes" reliable operation.

Probably the simplest fix would be just "hotter Pitot´s. And this can be "tested" by the "players". With benefits to A, B and other companies (and a/c operators, etc.)
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Old 16th Jun 2011, 15:50
  #40 (permalink)  
 
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syseng68k,

Presumably a tail-chute could be fitted, perhaps to a strengthened APU bulkhead. How its getting tangled-up with the APU (which might be running) could be prevented, I'm not sure.
Other problems
(1) It would have to be certificated for public transport, and presumably deployed on a test-flight.
(2) Would it be deployed automatically or manually (by crew action), and what criteria would be used?
(3) Would it subsequently be jettisoned automatically or manually (by crew action), and what criteria would be used?
(4) In the event of jettison failure, which might have followed unwanted deployment, would the aircraft be capable of maintaining level flight? (The second prototype BAC 1-11 had to make a very sudden forced landing on Salisbury Plain when it suffered this problem during deep-stall testing,)
Hard cases make bad law?

Re the uncommanded roll to the right as the AP disconnected, the BEA does not quantify it. Turbulence?

Like some others, I have a feeling that the PF may have experienced some difficulty in achieving left-stick without up-stick when unexpectedly handed the baby at 4am CET. I also hang on to the faint hope that the BEA may acquire ASI 2 data from the QAR. Unless it was over-reading, I cannot understand why he perpetuated the mistake as the aircraft climbed.
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