Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

AF447 Thread No. 3

Tech Log The very best in practical technical discussion on the web

AF447 Thread No. 3

Old 4th Jun 2011, 23:15
  #1381 (permalink)  
Posts: n/a

I think UAS was tracked well before 447 went in.

In the perhaps futile effort to get anyone to entertain other than "ICED PITOTS" I suggest that Unreliable airspeed does not mean "Reliable ICE"

It means that a system has become unreliable, and is being subtracted from a reliable scan, imho.

I submit that losing an engine should be orders of magnitude more dangerous than loss of a/s reads. Yet this failure has everyone's jock in a knot, and scattering to the books.

Steady. If Pitots have discrepant reads, or only one, and thus two of three samples are duff, what DJ77 intimates here is more interesting than Ice, and I submit, more likely.

It may be a wind tunnel snafu, a lack of extensive failure analysis, or simply the Bus' personality in "Severe Turbulences".

If she was behaving badly enough to elicit recovery inputs from our PF, and showed a tendency to roll ("Twitchy Ailerons"), plus an a/p trim that is thus far unknown, well, what is this obsession with ICE?

For all we know, she lost a radome into the F/O's Pitot. If one spends enough time with Vasquez' product, ICE is unlikely.
Old 4th Jun 2011, 23:15
  #1382 (permalink)  
Join Date: Feb 2008
Location: In the Old Folks' Home
Posts: 420
Received 2 Likes on 1 Post
I See It That Way

I may be the only person on Earth who sees it this way.
You're not.
Smilin_Ed is offline  
Old 4th Jun 2011, 23:29
  #1383 (permalink)  
Posts: n/a

From the outset, The principals were playing an immature game of "He did it".

One needn't be fluent in French to assimilate all the bs from those who we looked to for info. Airbus reissued a dog-eared "Mind how you go, Pilots". Air France started with "Our crew were perhaps unlucky with the radars" (read: incompetent). Then it was "lightnings". Then "Turbulences Forte".

ACARS was "LEAKED" boys and girls, and Monsieur leaker got no Pie.

This two year long exercise in Marketing, ass covering, and damage control hasn't affected my outlook one bit.

Kick ass, and take names.

I would step on a 777 with TRENTS tomorrow, in fact, next week I actually will. Mystery Fuel? No, it never happened. The actual problem was addressed, the TRENT got some mittens, although the bs flew for John and Jane Public, I warrant.
Old 4th Jun 2011, 23:47
  #1384 (permalink)  
Join Date: Sep 2009
Location: Around the World
Age: 74
Posts: 87
Likes: 0
Received 0 Likes on 0 Posts
bearfoil wrote:
One needn't be fluent in French to assimilate ....
For instance ... here (IMO, released 2009, sept.)
NeoFit is offline  
Old 4th Jun 2011, 23:54
  #1385 (permalink)  
Join Date: Jun 2009
Location: Brazil
Age: 76
Posts: 35
Likes: 0
Received 0 Likes on 0 Posts
Quite irrelevant

Weather radar showing a wind of 316km/h today, down here in Brazil as a cold front arrives in full force

yfrog Photo : http://yfrog.com/cabt5j Shared by cristianonoro
Gringobr is offline  
Old 5th Jun 2011, 00:06
  #1386 (permalink)  
Join Date: Mar 2008
Location: At home, retired 2012
Age: 75
Posts: 14
Likes: 0
Received 0 Likes on 0 Posts
gums: TOGA actions by the system?

It depends on the flap lever position.
If the lever is in the zero (up) position it will command thrust only, TOGA, max thrust setting.
Should the flap lever be in “one” or more, it will command the Flight Director bar, and A/P, if engaged, to Go Around. Pitch channel will go to Speed Reference System.
As you know, above a certain altitude, climb, MCT and TOGA are the same, as far as EPR or N1 are concerned.
jcarlosgon is offline  
Old 5th Jun 2011, 01:17
  #1387 (permalink)  
Join Date: Jan 2008
Location: uk
Posts: 857
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by DJ77
It is not known if similar events (simultaneous multiple pitot icing) ever happened on other than recent Airbus types. These incidents are not always reported by operators but perhaps someone started compiling statistics after june 2009. Yet the probes used by other manufacturers cannot be so different and were designed under the same certification requirements.
It is known, and the answer is that yes it does happen on other types and with other pitot types on the buses. It probably isn't always reported, but when it is, the reports are there to find. Certification requirements might vary - in the sense that Airbus is known to require wider range of operating environment testing than the regulations, and other mfrs may well do the same, but not exactly the same...

Could it be that this problem has more to do with the way they are installed than with the probes themselves (e.g. typical position on the fuselage)?
Could be, but there are many other variables to eliminate, and also the issue that on the same airframe, and same mount points, other pitot tubes have a much lower failure rate. Maybe, for whatever reason, the "bad" thales model tended to end up on 330s.
infrequentflyer789 is offline  
Old 5th Jun 2011, 02:11
  #1388 (permalink)  
Join Date: Dec 2010
Location: Middle America
Age: 84
Posts: 1,167
Likes: 0
Received 0 Likes on 0 Posts

Your post:
Lest we forget.
ChristiaanJ said......

"...engine-eer From another engineer...
I thought the basic problem with the pitots was that the certification specs themselves are totally obsolete..."

I think that is a red Herring, and it puts one in mind of the "As yet and heretofore "unknown characteristics of FUEL in icing at extremely low temps."

BA038 was surrounded by such "informed opinion" and the TRENT was modified by addressing its "Insufficiencies in thermal performance" rather than some exhaustive research into "dangerous" fuel.

Here, the same artifact of "Tacit" acceptance of what amounts to absolute bs.

The weakness of the Thales install was legend, as was (is) shortcomings in powerplants, avionics, etc.

For my money, I remember that the USAF has operated large subsonic a/c with swept wings at FL500 and above for more than fifty years. They heated their fuel, and if pitots were killing pilots.......

bear is also a cynic. I believe in an honest regulator, and an authority that not only does not give the players the "benefit of the doubt", but carries a small chip in the Public's interest, though they may walk with a "slight limp".

All in all, after thousands of pages of comment, the pitots were known junk, and the pilots acted to burn down the "status quo" (). AF changed out the junk, and what remains is for even an average attorney to make even a weak case. Air Travel IS safe, so safe I am incensed that weak kneed and less than honest folk chip away at it.

end rant.
You are not obviously an engineer and IMHO, you are over the top here. First, Thales does not make junk, neither does Goodrich. Fact is, pitot tubes do ice when encountering abnormal amounts of ice crystals, ice crystals+super cooled water, or supercooled water. This leads to the dreaded observed speed, either high or low. To claim that Thales makes junk, e.g. have a bunch of stupid engineers working there, while Goodrich makes the 100% perfect product is absolutely ludicrous. You should think about how many aircraft, Boeing, Airbus, MD, etc., are flying at this moment. They basically all fly a combination of either Thales or Goodrich pitot tubes. What you think you know, you don't know. That is, a complete story on pitot tube icing, unreliable air speeds across all operators, all makes of tubes, and all types of high flying commercial aircraft. It would seem that Thales pitot tubes on the A-330/340 aircraft do not perform as good when encountering ice crystals at high altitudes compared to Goodrich pitot tubes, but not by much. Goodrich tubes also ice over on A-330/A-340 and Boeings and other aircraft, why? It is because the design as being 99.99% foolproof only is true for those conditions that are, in reality, measureable and tested against. Both Thales and Goodrich tube met this criteria. Perhaps Airbus aircraft are more susceptible to pitot tube icing than Boeing or others, but that can only be supported by actual data of the entire flying base that isn't apparent at the moment. What is not measureable, is pitot tube behavior at high altitudes, high mach numbers flying through ice crystals, ice crystals+supercooled water or supercooled water. Until such time someone develops a test cell to create an air speed of mach 0.83-0.86, identifies the geometric makeup and size of ice crystals at 30K-40K altitudes along with the ability to inject supercooled water into the equation, we will not have the "eutopia" you seemingly are looking for in terms of pitot tube 99.99% reliability.

Face the facts, other aircraft have had erroneous airspeeds occur as the result of iced pitot tubes and they recovered and went on. The question for AF447 is why did they not recover and go on, don'tcha think?

Also, don't relate it to the BA Trent/777 incident. That is like comparing apples to pumpkins.

I am an engineer and engineers in the aerospace business do not develop "junk" as you suggest as in the case with Thales. Your just P***ing into the wind.
Turbine D is offline  
Old 5th Jun 2011, 04:11
  #1389 (permalink)  
Posts: n/a

I am surprised. I know you are an engineer, so I am surprised. What I call the Thales is irrelevant, and for purposes of pragmatic discussion, the Pitots fit to this a/c were in fact junk. Insufficient performance? Eccentric behaviour in some frequently encountered flight envelopes that crashed autoflight in commercial carriage? That is somehow excusable? A legacy carrier is faced with a mutiny when critical personnel refuse to fly with it attached to their a/c?

I am over the top? A very low Top, I would say. At no time have I advocated for a competitor of Thales, ever, nor would I. The salient discussion involves equipment that could not perform that may have directly caused the deaths of many people?

Now this may not be true, and the marketplace is a brutal arena where rumor can kill a product. However, the shortcomings of this device were known, PATENT, and disregarded.

BA038 is precisely the example I wish to portray. It frames the nonsense involved in the drama of manicuring a platform for continued suitability (and profitability) in the market.

you said:

"...Until such time someone develops a test cell to create an air speed of mach 0.83-0.86, identifies the geometric makeup and size of ice crystals at 30K-40K altitudes along with the ability to inject supercooled water into the equation, we will not have the "eutopia" you seemingly are looking for in terms of pitot tube 99.99% reliability..." This is exactly what Boeing and Rolls did in Renton re: BA038. Apples and Pumpkins?

Air France R&Red the Thales, and the pilots kept flying. I vote with the Pilots, here; the engineers lost their voice?

While we're at it, let's look at the Laws between Normal and Direct. They are all some step children of Normal, and require pilots to adopt a computer like mode of problem solving, instead of trained in and immediately available skill sets. If any time until the day I die, I hear the horn, or feel the shaker, I could be fast asleep, I will push. THIS fbw does not respect the ultimate failure, it gives itself a built in excuse, "It did everything it was supposed to do".

Except butt out?

much respect, TD
Old 5th Jun 2011, 04:57
  #1390 (permalink)  
Join Date: Jul 2009
Location: Texas, USA
Age: 70
Posts: 13
Likes: 0
Received 0 Likes on 0 Posts
"We have no valid indications"

Having finally caught up to real time on this thread, I would like to bring up something that occurred to me on first reading of the (English translation) of the BEA Update of 27 May, but which does not seem to have been discussed on this thread. The Update states that
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".
Assuming these statements by the pilots have been translated accurately, I believe they were seeing far more inconsistencies on their cockpit displays than just UAS. I would not expect a pilot who doubted just the validity of his airspeed or just the stall warnings to refer to the situation as "no valid indications." It seems to me that either most of the information on their PFDs was non-sensical, or by 2:12:02 their loss of situational awareness was so severe that they were no longer trusting any of the instruments even thought some may have been valid.

I wonder whether their inability to recognize the stall was the result of incorrect, absent, or non-trusted attitude information? Even though the IR portions of their ADIRUs were functioning properly, might the system-detected invalidity of air data and/or AoA information have affected the display of what should be purely-inertial information? (Later on the same page the BEA makes reference to "angle of attack, when it was valid ..." which suggests they have DFDR evidence of invalid AoA readings.)
MFgeo is offline  
Old 5th Jun 2011, 05:07
  #1391 (permalink)  
Posts: n/a
@Gringobr, Impressive windspeed indeed... It has nothing to do with this accident though, but points at an interesting detail:

The question is not *why* the pitots froze (in a FL550 TOPS CB, *any* pitot will freeze!), it's *what* on earth they were doing there!
Old 5th Jun 2011, 05:20
  #1392 (permalink)  
Join Date: Jul 2002
Location: 40N, 80W
Posts: 233
Likes: 0
Received 0 Likes on 0 Posts
Several people have noted the 61° AoA of the mainplane and the 45° angle of decent, and agreed that the mainplane was therefore fully stalled.

With a nose-up up-trim of 13° the HS had an AoA of about 48° and was therefore also fully stalled, also with an angle of decent of 45°.

Although the mainplane and HS both had airfoil geometries, they seem to me to have been acting more like two drag-parachutes lowering the aircraft towards the sea.

In fact this arrangement was the answer to the problem that Burt Rutan had to solve it getting his Spaceship 1 safely back from supersonic speeds in space to low sub-sonic speeds in the lower atmosphere.

Spaceship 1 was a variable geometry air/spacecraft in which the tail could be trimmed to a nose-up of about 45°, which was enough to guarantee that both the mainplane and the tail would be fully stalled and act as drag-parachutes, bringing the aircraft back to a low altitude at a safe speed, without any other pilot action.

Once at a safe altitude Spaceship 1 could be trimmed back to normal, and safely transitioned into a glide back to the ground.

Gums Post #771 5th May 2011, 23:45 contains a description of a deep stall in an F-16:

.... with no buffet, vibration, or noise. ……”

That sounds to me as quiet as a parachute drop.

I wonder if that is what it seemed like on AF447?

Maybe a Spaceship 1 pilot (or passenger) could tell us on this thread what a Spaceship 1 re-entry feels like?
PickyPerkins is offline  
Old 5th Jun 2011, 06:08
  #1393 (permalink)  
Join Date: May 2011
Location: US
Posts: 6
Likes: 0
Received 0 Likes on 0 Posts
Je ne comprends rien.

In addition to "We have no valid indications", a couple articles I saw say that the last thing one of the pilots said near the end of the sequence was, "Je ne comprends rien" which means "I don't understand anything."

When automation kicks out (essentially fails) because of conditions, at the least what is left should benefit the pilots dealing with the situation and not confuse it further. What I'm saying is, it seems that some of the bells and whistles sounding once auto pilot kicks out, are remnants from earlier development (older systems) which are a residue which need to be reconsidered, not from the point of view of each individual signal, but the over all effect and usefulness at extreme moments.
Can't there be a redesign of support for extreme moments?

As DozyWannabe said, "The fact is that when you have pitot/static failure, all bets are off when it comes to warnings/indications and the crew must concentrate extremely hard to work out what's going on."
alex_brin is offline  
Old 5th Jun 2011, 06:40
  #1394 (permalink)  
Join Date: Oct 2009
Location: berlin
Posts: 152
Likes: 0
Received 0 Likes on 0 Posts
PP not even spaceship1 uses this configuration to create a auto-stable decent, a lot of free flown modells uses this as save thermal-brake since a long time

released with a glimm-rope or a smal timer the horizontal stabilisator moved up after some minutes, and the following flight path is very stable with not to much downspeed,
the model sinks faster than the updraft thermik may be and landed without high-speed-chrash on earth........

if a trim +13deg for an a330 seems very stable for 45° angle of decent....

can it be that today some pilot did not know (learn) the trim value for a stable glide with 3° or 4° angle of decent? is the understanding of the aerodynamic mechanism of an auto-stable flow (glide) no longer notable fore every pilot?

trim, position of CG.....is today every basic thing out of mind?

every pilot has to build and flow free flow models before he learn to control computers
grity is offline  
Old 5th Jun 2011, 08:42
  #1395 (permalink)  
Join Date: Nov 2010
Location: Europe
Posts: 21
Likes: 0
Received 0 Likes on 0 Posts
Still a very interesting thread over here !

I couldn't find the info in the A330 FCOM but maybe some of you have the answer:

It seems that the PF struggled with lateral stability issues.

In normal law operation, not only the ailerons but spoilers except #1 might be extended depending on air-speed to increase the rate of turn.

How would the spoilers respond in alternate law when full-lateral-stick deflection is applied and speed is missing/incorrect ?
chaz88z is offline  
Old 5th Jun 2011, 09:21
  #1396 (permalink)  
Join Date: Jan 2008
Location: Australia
Posts: 50
Received 0 Likes on 0 Posts
Gums, that was a very interesting publication you linked to, thanks.

This passage jumped out to me:

The traditional approach to stall training consisted in a controlled deceleration to the Stall Warning, followed by a power recovery with minimum altitude loss.
Experience shows that if the pilot is determined to maintain the altitude, this procedure may lead to the stall.
A practical exercise done in flight in DIRECT LAW on an A340-600 and well reproduced in the simulator consists in performing a low alti- tude level flight deceleration at idle until the SW is triggered, and then to push the THR levers to TOGA while continuing to pull on the stick in order to maintain the altitude.
The results of such a manoeuvre are:
  • In clean configuration, even if the pilot reacts immediately to the SW by commanding TOGA, when the thrust actually reaches TOGA (20 seconds later), the aircraft stalls.
  • In approach configuration, if the pilot reacts immediately to the SW, the aircraft reaches AoA stall -2°.
  • In approach configuration, if the pilot reacts with a delay of 2 sec- onds to the SW, the aircraft stalls.
This shows that increasing the thrust at the SW in order to increase the speed and hence to decrease the AOA is not the proper reaction in many cases (this will be developed in the following chapter).
In addition, it is to be noticed that, at high altitude, the effect of the thrust increase on the speed rise is very slow, so that the phenomenom described above for the clean configuration is exacerbated.
auraflyer is offline  
Old 5th Jun 2011, 10:04
  #1397 (permalink)  
Per Ardua ad Astraeus
Join Date: Mar 2000
Location: UK
Posts: 18,579
Likes: 0
Received 0 Likes on 0 Posts
syseng - if you dig out the PGF Airbus accident thread you will find some good flow charts of software logic there (I think from PJ2).

I am now reeling in a state of shock to find that there are not just 2 'Alternate Law' programmes but at least 5 (Post #1311) and I am wondering how on earth a human is supposed to work out wtf is going on - or perhaps he/she isn't?

I suggest that if the 'finding' is 'pilot error' it may well be quite 'excusable'.

It seems that a number 1 priority is that AB recognise that their aircraft can stall and sort out the stall warning logic so that mere humans can see what is actually happening.

The earlier query about misleading attitude information is a good one - we have 'accepted' that because of the ACARS stream the ADIRUs were delivering correct information - but this could be wrong, of course.
BOAC is offline  
Old 5th Jun 2011, 11:27
  #1398 (permalink)  
Join Date: Jun 2011
Location: UK
Age: 83
Posts: 19
Likes: 0
Received 0 Likes on 0 Posts
Looks to me as if an Airbus pilot needs more skills and training than average.
t54 is offline  
Old 5th Jun 2011, 11:45
  #1399 (permalink)  
Join Date: Mar 2006
Location: Choroni, sometimes
Posts: 1,974
Likes: 0
Received 0 Likes on 0 Posts
DUBAI— The Airbus A380, which is considered as the world's largest
long-haul airplane featuring two decks, four aisles and the capability to
carry 600 to more than 800 passengers on board, is also a "zero-crash

"Technology is what we master at Airbus. We just cannot afford to crash. The
A380 has been designed to be a zero-crash aircraft and we made sure that it
carries passengers safely to and from their destinations," said Jacky Joye,
flight test engineer of Airbus.
What about A330 Mr. Joye?
hetfield is offline  
Old 5th Jun 2011, 12:26
  #1400 (permalink)  
Join Date: Dec 2002
Location: Europa
Posts: 612
Likes: 0
Received 0 Likes on 0 Posts
Exclamation Power application is NOT stall recovery

"This shows that increasing the thrust at the SW in order to increase the speed and hence to decrease the AOA is not the proper reaction in many cases"

Sadly both FAA and JAR approved schools are training pilots in a flawed manner by the insistence on a minimum height loss instead of getting the wings flying again. How does a glider recover from a stall?

JAR 25 / FAR25 Test Pilots always pitch to reduce AoA long before adding power to recover from stall.

Reducing the Angle of Attack (AoA)/Aircraft Attitude to unload the wing and reattach the airflow is the key BEFORE applying power once speed is about 20% above stall speed.

Most Commercial Pilots are taught to operate safely and effectively within a flight regime of up to +/- 60 deg Angle of Bank and +/- 30 deg pitch. However, the majority of Flight schools on both sides of the Atlantic seem to teach Full Power as part of a Standard Stall Recovery (SSR). The Royal Air Force's Central Flying School also teaches SSR but the emphasis is on reducing AoA to remove buffet whilst simultaneously adding power - not holding the pitch attitude as suggested. Holding the pitch attitude whilst applying full power is a Low Level Windshear/Terrain avoidance manoeuvre not a stall recovery technique! The emphasis on minimum height loss at the stall by some Flight/Simulator examiners on check rides has exacerbated the issue.

Propellor Aircraft:

The idea that this technique worked for stall recovery on 1950s piston powered aircraft is inaccurate. As Sean Roberts of the National Test Pilot's School explained at the Bombardier Safety Standdown, all aeroplanes with tractor propellors will pitch up with application of power due to propellor normal forces. This is as true for WW2 fighters as for 2011 Turbo Prop Twins.

At high AoA, the propellor slipstream is deflected downwards. By Newton's laws, the opposite reaction is the propellor normal force which causes the nose to pitch up as full power is applied. At the same time, the local angle attack of the wing immediately behind the slipstream will be very slightly reduced (increased local dynamic pressure) but the rest of the wing will stall from the wing tips inwards. Without an increase in CLmax (eg: flaps), the stalling speed will not change significantly but the effect of power will increase the pitch attitude at which the stall occurs.

Asymmetric Blade Effect:

We now have a high nose attitude senario with further buffet onset and a greater likelihood of un-demanded roll or yaw. The latter caused by a combination of one wing tip stalling before the other and asymmetric propellor blade effect. Test Pilot, Sean Roberts, uses the helicopter rotor as an example (c.f. 90 deg AoA on propellor blade). Unless you are flying a machine with counter rotating propellors, the difference between the advancing and retreating blades creates asymmetric propellor disc loading which will yaw the aeroplane (For conventional US engined aircraft, Clockwise rotation to Pilot, will yaw left). What started as a basic stall recovery is now a more serious aircraft upset made worse by the pilot applying power at high AoA.

Buffet (stall) + un-demanded roll or yaw = SPIN !

Modern Jets:

Underslung engines on A320/B737/EMB175 all pitch up with power application without automatics in play. Rear Mounted Engined aircraft like the MD80/Citation XLS/Gulfstream VI are far less susceptible to power on pitch up unless the airflow has already separated from the wing and turbulent flow is ingested into the engines creating compressor stall /rollback.

Swept wings complicate stalling matters further. The downwash effect of trailing vorticity on a swept wing is quite different to a straight one. The overall result is less downwash at the wing tips than inboard. On a tapered swept wing there can even be upwash at the wing tips. This means a swept wing will stall at the tips first leading to a nose up pitching moment as the centre of lift moves forward thus increasing the stall in a runaway manner. Better wing design (wing fences, vortex generators, slat operation, etc), and advances in Control Systems have largely overcome these issues but a forewarned pilot is a safer one.

In summary, at the first symptom of a wing stall, reduce AoA (unload) and accelerate to 1.1 Vs before applying power. Better still (prevention being better than cure) stop the stall happening in the first place by monitoring flight path (AoA, lift vector, energy management) and the automatics. Prioritise by setting appropriate aircraft AoA/attitude and Power in the unlikely (but possible) even the computers do drop out.
angelorange is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.