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

AF 447 Search to resume (part2)

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

AF 447 Search to resume (part2)

Old 14th May 2011, 19:02
  #1341 (permalink)  
 
Join Date: Feb 2011
Location: Nearby SBBR and SDAM
Posts: 873
Not a "graceful degradation" after 02:13:08

takata,

As i understood after 2:13:08 ACARS show the a/c "resources" further degraded and the crew no longer "could use" ISIS and IR´s. It is not true?

post #1343 was edited as suggested by you.
RR_NDB is offline  
Old 14th May 2011, 19:12
  #1342 (permalink)  
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 77
Posts: 1,330
HN39;
It is the fuselage violently veering to the right which 'twists' the frames.
I had refrained from making a comment, following your much earlier post where you considered the bank was to starboard rather than my posited port. The reason for my delay centers around the term "yaw" and its interpretation when related to the BEA's use of it in the end of flight events.

My interpretation was that the term "yaw" was being used to describe the aircraft rotating clockwise in a near horizontal plane about a fulcrum nominally near its CoG while airborne - (spin?).

Your interpretation (I believe), is that the "yaw" was introduced by the #2 engine digging in and creating the "tail yawing to port" event which resulted in the damage described and allowed the safe departure of the Vertical Stabilizer as the empennage dug deep into the water - probably collapsing and shearing off at the aft pressure bulkhead. The high CoG of the V/S and its own inertia then completed its final disengagement, allowing it to flop into the water on its port side. The APU, having being punched from its mounts gave a glancing blow to the rudder (as it swung hard to port following the loss of the hydraulics), then commenced its journey to the bottom.

I can go along with the above, but when introducing the "en ligne de vol" business plus the high RoD, the time between #2, the tail and #1 digging in, was in the order of milliseconds. Not enough time to overcome the moment of inertia already committed to the "en ligne de vol". As an after thought, and to just muddy the waters some more; - if the horizontal component of the aircraft's trajectory was say 30° to port of the "heading" at time of impact, the same damage would most likely occur.

It is rather academic at this time, but the actual rationale used by the BEA in making their interim conclusions would be interesting to know.

Last edited by mm43; 14th May 2011 at 21:26. Reason: spelling!
mm43 is offline  
Old 14th May 2011, 19:21
  #1343 (permalink)  
 
Join Date: Jan 2008
Location: Blighty (Nth. Downs)
Age: 73
Posts: 2,083
gums, Quote:
"Having flown the first "operational" full FBW system, I was a non-volunteer test pilot, as were all of us in those days ( 1979 and a few years thereafter)."
The first year of ops on the A320 (1988) was a bit like that, in a low-key way.

Quote:
"We clever pilots can find ways to "beat the system". We can do things that the engineers and others never envision ( see Perpignan, for example, or the first crash with a high-time pilot making a low pass for public relations)."
Yes, flew with one or two guys who aspired to be test pilots. (Why don't we switch off an ELAC and one/two SECs, and get some useful practice in Direct Law? Not today, thanks.) We managed to avoid a Habsheim.
There was a subtle "trap", though, involving the A/THR and FD. In descent in OPDES, the A/THR is in idle mode, and the selected IAS is controlled by elevator (i.e., conventional). If you come into the circuit and elect to go visual, you may elect to dispense with the AP & FD, but retain A/THR. If you level off a bit at (say) 3000ft when the FMGC thinks you still want descent in idle thrust to (say) 2000ft, the speed will naturally fall below target. In those days, the first intervention from the A/THR would be Alpha-Floor (TOGA thrust) as the stall protections kicked-in. Good way to mess up your visual approach... We soon learned to switch both FDs off: to tell the A/THR we wanted it to control the speed for us (and avoid conflicting FD pitch-commands). That had not been originally established as an SOP.
Word did not filter through to one Asian operator, however, and it lost an aeroplane on the approach at Bangalore. The crew had wound the ALT selector down to zero, I think, retaining OPDES, so the thrust needed at about 500ft never materialised. (Bit like the B777 at LHR; reason totally different.)
Post-Bangalore, one of gums's software changes ensured that the A/THR automatically comes out of idle mode if the speed falls below Vls.

Airbus FBW architecture is now a mature system, with tens of millions of flight hours behind it, so simple surprises like that are highly improbable in the case of AF447. But airline pilots do not generally explore the boundaries of the flight envelope, so the learning process is not as brutally quick as on the F-16.

Quote:
"So my personal observation is that this accident will be found to be in the category of "unplanned flight conditions", possibly complicated by one or two sensor failures.
I also see a few modifications coming for the 'bus control laws. It's digital, right? So not a lotta hardware needed, just some good flight tests with modified control laws/reversion sequences."

gums, you could be proved right.
Chris Scott is offline  
Old 14th May 2011, 19:41
  #1344 (permalink)  
Thread Starter
 
Join Date: Jun 2009
Location: florida
Age: 77
Posts: 1,141
Auto throttle authority

Salute!

Well, Chris, I pray that I am close to the scenario, and that we let the crew, et al rest in peace after their efforts to get the plane under control. We shall see.

The Hornet has auto-throttle, but it is not tied as closely to the overall control laws and autopilot modes. 'bird can explain better, but the Navy troops liked an approach that used AoA to control speed and throttle to control descent rate. We airdales normally pointed at the end of the runway and used throttle a lot more than AoA for speed. I used more of the "squid" approach procedure after getting bit in the butt one night in the SLUF, and flew at best AoA, using throttle for whatever it took. In short, I didn't worry about a grease job.

Something bugs me when I can't "push it up" with those levers and command more thrust.

I only flew one jet with a good autopilot approach mode, and it did not have an auto-throttle. It had good AoA/pitch rate protection and followed the ILS like a dream. Would watch the stick move back and forth as "we" came down the glide path ( F-101B, so it was a family jet. Heh heh). Runway environment in sight? Voila! Hit paddle switch and land the sucker.

Make no mistake. I do not want to see complete control of the control surfaces in a FBW jet. The things are designed with different aero considerations than "conventional" designs.

So I await the data plots, as most do.
gums is offline  
Old 14th May 2011, 19:44
  #1345 (permalink)  
 
Join Date: Jun 2009
Location: Paris
Posts: 691
Mac,
Originally Posted by RR_NDB
As i understood after 2:13:08 ACARS show the a/c "resources" further degraded and the crew no longer "could use" ISIS and IR´s. It is not true?
Well, thank you for taking my remark into account.
My answer to your question will be no, as per the BEA "interim conclusion" from their ACARS study:

F-GZCP - 1st June 2009, BEA report #2 p.41

1.16.2.4.5 Partial conclusion on the analysis of the messages:
At this stage of the investigation, analysis of the messages makes it possible to highlight an inconsistency in the speeds measured just after 2 h 10 which in that minute generated ten of the twenty-four maintenance messages. Eleven other messages generated between 2 h 10 and 2 h 14 can also be linked to anemometric problems (inconsistencies in the speeds, low speeds and/or erratic speed values).

* The aircraft switched to alternate 2 law in the minute at 2 h 10 and remained in that law until the end of the flight..

* No message present in the CFR indicates the loss of displays or of inertial information (attitudes).

Note: in addition, as the ATSB mentions in its second interim report(3) on the incident to the A330-300 that was performing flight QF72, in relation to problems with ADIRU’s, the maintenance messages relating to the events on flight AF447 and fl ight QF72 show significant differences, both in their sequence and in their content.
takata is offline  
Old 14th May 2011, 19:45
  #1346 (permalink)  
 
Join Date: Dec 2010
Location: Middle America
Age: 80
Posts: 1,153
takata

Thanks for your response regarding the pitot tube heating question.
Turbine D is offline  
Old 14th May 2011, 19:46
  #1347 (permalink)  

Sun worshipper
 
Join Date: Dec 2001
Location: Paris
Posts: 494
HazelNuts39
It is the fuselage violently veering to the right which 'twists' the frames.
Les déformations des cadres montrent qu’ils se sont rompus dans un mouvement vers l’avant avec une légère composante en torsion vers la gauche.
( From the 1st interim report)
One of the aspects of your argument that bug me is the association of a *slight torsion component to the left* with a violent *veering to the right*

The second interim report explains the stresses involved thus :
"The vertical stabiliser’s side panels did not show signs of compression damage.
The breaks seen at the level of the lateral load pick-up rods were the result of the backwards movement of the attachments and centre and aft frames. The observations made on the vertical stabiliser are not consistent with a failure due to lateral loads in flight.
The observations made on the debris (toilet doors, partitions, galleys, cabin
crew rest module, spoiler, aileron, vertical stabiliser) evidenced high rates of
compression resulting from a high rate of descent at the time of impact with
the water.
This high rate of compression can be seen all over the aircraft and symmetrically on the right- and left-hand sides.
High levels of loading would be required to cause the damage observed forward of the vertical stabiliser (compression failure of the forward attachment).
These observations are not compatible with a separation of the aft part of the fuselage in flight.

The damage found at the root of the vertical stabiliser was more or less
symmetrical, as were the deformations due to the high rate of compression
observed on the various parts of the aircraft. This left-right symmetry means
that the aircraft had low bank and little sideslip on impact.(which shoots down the sideslip theory, too )
The deformations of the fuselage frames at the root of the vertical stabiliser
were not consistent with an aircraft nose-down attitude at the moment of
impact".


All the above makes me think that the slight torsion to the left component of the stress forces on the frame came from a yawing moment to the left, therefore a slight left wing low attitude at impact.
Lemurian is offline  
Old 14th May 2011, 20:18
  #1348 (permalink)  
 
Join Date: Jul 2009
Location: UK
Posts: 133
Originally Posted by takata View Post
In auto mode, the amount of heat provided by the heaters is modulated following what the "probes" themselves are sensing. When anti-ice is selected ON, full heating is provided, whatever the "probes" are sensing. It makes sense if you are considering that the "probes" are freezing because the heaters were not delivering the correct amount of heat at the first place.

In fact, it seems that those probes freezing at cruise are not related to temperature (really) changing but to those specific (very small) ice particles melting when such conditions are encountered (mostly in tropical weather). Hence, TAT will increase very fast and reach a level close to 0°C (iced particles temp melted on the TAT probes). The drawback is that you can not fly with anti-ice ON all the time as it can also damage all the systems by overheating the probes. Hence, it should be selected on purpose.
I'm sure I will be corrected if wrong, but I believe the issue with pitot tube heating is only when on the ground - no problem dissipating 300+ W when exposed to cold flight-speed air, but they'd glow red hot if left on on the ground! So the auto control will be very simple - as all safety critical systems should - to be easily testable, and surely a cut-off temperature would be near +40 degC than near ice-point?

I am not a big fan of the super-cooled icing theory, I suspect the current issue still subject to research is due to the way certain distributions of micro-fine ice particles (i.e. what makes up different clouds) pack acting as an insulator so there is poor heat transfer from the heated metal to the ice blockage. If it is the type of cloud - then I don't like the odds when identical probes pointing into the same one, that any 2 out 3 may be adversely affected in exactly the same way. If I was responsible for the pitot-tube detail design I would pay most attention to the drain hole and make sure that is always kept clear - meaning the most likely failure mode would be for value to fall to zero - easily detectable. Early Thales pitot tubes had poorly manufactured drain holes, burrs left which encouraged solid deposits and blocking, but sure this not now an issue.

As discussed many times drain hole blocking on its own would cause a small over-read, both ram and drain blocked could lock an old speed value in, but may be difficult to detect because speed reading still live - varies with static pressure reading/altitude. Worst time for this to happen would be during a commanded climb or speed change.

The pitots may only all disagree only when they melt out differently, so what was happening just before 02:10?
sensor_validation is offline  
Old 14th May 2011, 20:22
  #1349 (permalink)  
 
Join Date: Feb 2011
Location: Nearby SBBR and SDAM
Posts: 873
Resources degradation after 2:10:10

Takata,

Looking to my bookmarks i found:

http://www.iag-inc.com/premium/acars2.pdf

I read both BEA´s I and II.

I was always considering a very serious degradation as a fact.

Another crucial point we must wait for FDR contents.


As i understand now the analysis of the link above is at least, "baseless" or even worse.
RR_NDB is offline  
Old 14th May 2011, 20:28
  #1350 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 80
Posts: 1,689
mm43;

In my mental 'model' the right wingtip digs in at about the same time as engine #1. Due to the difference in moment arm, the yawing moment imparted by the wing tip may well be greater than that of engine #1.

lemurian;
From page 27 of BEA's #2:
The part of frame 87 that can be seen had undergone S-shaped deformation: the left-hand side forwards, and the right-hand side backwards.

Last edited by HazelNuts39; 14th May 2011 at 20:51.
HazelNuts39 is offline  
Old 14th May 2011, 20:40
  #1351 (permalink)  
 
Join Date: Mar 2007
Location: under the sea
Posts: 2,355
"In auto mode, the amount of heat provided by the heaters is modulated following what the "probes" themselves are sensing. When anti-ice is selected ON, full heating is provided, whatever the "probes" are sensing. It makes sense if you are considering that the "probes" are freezing because the heaters were not delivering the correct amount of heat at the first place."
That is not how I read 1.30.50 p1/2.There are two heating modes with Airbus,low heat on the ground and high heat when airborne for the pitots.There have been numerous incidents where this changeover has not occurred giving the crew lots of problems.I have also seen where the pitots have cooked in the sun of the Indian Ocean to a threshold above the warning causing nuisance ecam.
tubby linton is online now  
Old 14th May 2011, 20:53
  #1352 (permalink)  
 
Join Date: Aug 2009
Location: Germany
Age: 63
Posts: 1,809
Cool

Hi,

The only false idea is if one will claim that we could make flying an aircraft "100% safe" in every possible situations. Automatisms would make them "safer" in most situations... but not extreme ones.
I wonder whether it is thanks to these automatisms that the aircraft most often is near extreme situations
If the pilot do not have the FBW and an autopilot ... I wonder if by themselves they would go at altitudes and speed close to the coffin corner (extreme situation) to make their cruise if they have to handle their plane manually
jcjeant is offline  
Old 14th May 2011, 21:33
  #1353 (permalink)  
 
Join Date: Jun 2009
Location: Paris
Posts: 691
Originally Posted by tubby Linton
That is not how I read 1.30.50 p1/2.There are two heating modes with Airbus,low heat on the ground and high heat when airborne for the pitots.There have been numerous incidents where this changeover has not occurred giving the crew lots of problems.I have also seen where the pitots have cooked in the sun of the Indian Ocean to a threshold above the warning causing nuisance ecam.
There isn't an auto mode on the ground [edit, until one engine is running], only manual mode [for test if one engine is not running]. Auto mode [is always set] once the aircraft is airborne. Probe heating is then monitored and computed, by those three independant PHC (Probe Heat Computer). What do you think that will feed the PHCs with curent air data beside those probes themselves?
Nonetheless , if any probe icing is suspected during the flight => in auto anti-ice mode, you may ask for more heat (than computed) by pressing the anti-ice buton.
You'll need to refer to the "icing" part on the manual as I'm answering from memory without a single look at it.

Last edited by takata; 14th May 2011 at 21:52.
takata is offline  
Old 14th May 2011, 21:45
  #1354 (permalink)  
 
Join Date: Feb 2011
Location: Nearby SBBR and SDAM
Posts: 873
Advanced Systems

Hi,

The reason to use all this new solutions (FBW, complex control laws, etc.) is to "optmize" the performance (less weight, more resources, more profit margins, etc.) and last but not least, to have a safer machine ("protected", with good human-machine interface, etc.).

Naturally these "Advanced Systems" would operate in "regions" not usable by "conventional designs

When for any reason you have a problem i understand the "Advanced System" (the crew and the "super bird") will be closer to the limits (the mentioned extremes).

The reason for the recovery of the China 747 upset probably is related to the "lack" of optimization (in several aspects) of the a/c.

The toll always must be paid. And after paying it we "upgrade" the original solutions. (sometimes just by a new "software release"). EADS is paying the toll ahead of the competitors IMO simply because introduced "Advanced Systems" earlier, for the airlines. An "inexorable" trend.
RR_NDB is offline  
Old 14th May 2011, 21:50
  #1355 (permalink)  
Thread Starter
 
Join Date: Jun 2009
Location: florida
Age: 77
Posts: 1,141
Erroneous air data

Salute!

PLZ look at the B-2 crash at Guam

No icing.

Tubes with moisture and actual water - yep!

Loss of control at WoW? Yep.

I would not trust a sensor that has its own logic to determine if it is unreliable. Anybody else here think that way?

Granted, we can have only so many sensors to check on the other sensors. So maybe we should look at sensors that can stand zillions of degrees of temperature, but still measure vital dynamic and static pressure within some zone of accuracy. We don't need +/- 1 degree of temperature, +/- 100 feet of altitude, or even +/- 5 knots of speed.

There are major aero considerations determining favorable flight characteristics than a few degrees here, a few knots there, a few feet of altitude there. GASP!!

P.S. Getting too chatty here, so I shall chill for a bit.
gums is offline  
Old 14th May 2011, 22:00
  #1356 (permalink)  
 
Join Date: Feb 2011
Location: Nearby SBBR and SDAM
Posts: 873
Redundancy always benefit

Hi,

I would not trust a sensor that has its own logic to determine if it is unreliable. Anybody else here think that way?
When possible i aways use a redundant "info source! (with a different working principle) for my decision making. With 3 (odd)* much better.

* Allowing a voting scheme
RR_NDB is offline  
Old 14th May 2011, 22:15
  #1357 (permalink)  

Sun worshipper
 
Join Date: Dec 2001
Location: Paris
Posts: 494
HzelNuts39
lemurian;
From page 27 of BEA's #2:
Quote:
The part of frame 87 that can be seen had undergone S-shaped deformation: the left-hand side forwards, and the right-hand side backwards.
Regards,
Yes !
Just imagine a loop with an axis that goes top to bottom and someone turns the loop around that axis. The only movement that will cause a deformation as described above is a counter-clockwise rotation, i.e. a yaw motion to the left, and that's what I've been seeing for the past 17 months.
Lemurian is offline  
Old 14th May 2011, 22:33
  #1358 (permalink)  
bearfoil
Guest
 
Posts: n/a
mm43

...I see your point, a "Yaw" is a rotation, "nose right" is merely a crab. Whichever engine "digs in", the a/c has little time to accelerate around its "anchor" horizontally, the vertical is too fast. If the impact was mostly vertical, (BEA), the fuselage may have ruptured in classic form, fore the wing and aft, perhaps the tail separating at the Aft Bulkhead, the cockpit at the forward door. (The cockpit was close to, but separated from, the forward door, number one on the sea bed).

The VS hoops were deformed in a manner suggestive of a vertical exit with a slight twist to port (BEA), and relative to the fuselage.

I suggest it is not indicated that the tail hit first, number one, the Deck angle for tail strike is 17 degrees, and then only the belly portion at the break, up toward tail cone.

For the Empennage to hit first requires a deck angle of more than 17 degrees, and when adding that to the airflow, we approach rather closely to an AoA in excess of 90 degrees. Not supportable, unless in the rather wide parameterds of the Bear.

mm43..........
"....resulted in the damage described and allowed the safe departure of the Vertical Stabilizer as the empennage dug deep into the water - ...."


Hazelnuts39....

"In my mental 'model' the right wingtip digs in at about the same time as engine #1. Due to the difference in moment arm, the yawing moment imparted by the wing tip may well be greater than that of engine #1."


Hmmm..... How can right wing tip and #1 both be in the water and #2 DRY???

Last edited by bearfoil; 14th May 2011 at 22:55.
 
Old 14th May 2011, 22:40
  #1359 (permalink)  
 
Join Date: Feb 2011
Location: Nearby SBBR and SDAM
Posts: 873
Redundant air speed sensor/measurement principle (Laser based)

Hi,

A new way to measure an aircraft’s air speed using ultraviolet [email protected] has been developed by the BAE. By using the unique properties of light, this technique works at any altitude and even at low speeds where conventional methods struggle.
Link

Is this sensor operational today?
RR_NDB is offline  
Old 14th May 2011, 23:16
  #1360 (permalink)  
 
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 77
Posts: 1,458
The new [email protected] air speed system gets round these problems by bouncing light off air molecules and analysing the changes in reflection caused by the air’s motion relative to the aircraft.
It would seem likely that they are at a resonant frequency for one of the constituent bonds, likely N-N or O-O bond (N2 or O2) and thus able to get an absorbtion and re-radiation of the emitted energy. ie. a return that does not require dust, water droplets, or any other reflective constituent in the atmosphere. Pitot tubes-move over. Now we will just have to figure out how to keep the bugs off the "window".

Last edited by Machinbird; 14th May 2011 at 23:32.
Machinbird is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.