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

AF 447 Thread No. 7

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

AF 447 Thread No. 7

Old 14th Dec 2011, 13:04
  #641 (permalink)  
 
Join Date: Aug 2011
Location: Grassy Valley
Posts: 2,074
Likes: 0
Received 0 Likes on 0 Posts
VGCM66

Thank you sir. In your link, we read an opinion from BEA as to what the crew "concluded". On its face, this statement is preposterous, since it imputes conclusions to the pilots based only on comment they made earlier. No one in public knows what the pilots were thinking, and BEA, having tipped their hand, may know, and appear to be rigging the playing field.

BEA present it as fact.

This release contains condemnation of Airbus and the airline sufficient to confirm my proposal. Read it with care, allow for some interpretive changes, and the accident falls to Airbus almost completely.

This fatal wreck happened in the ten seconds post a/p loss, and the pilots, though involved, were not entirely responsible. One needs to take the BEA with generous portions of salt. What about "Rapid Climb", and "the aircraft was not immediately responsive" sounds familiar? Think of another similar incident, one with a better outcome.

@Machinbird. Your cite of PIO is instructive. You neglect another form of out of sync C/R.

Autoflight induced oscillation. AIO.
Lyman is offline  
Old 14th Dec 2011, 14:26
  #642 (permalink)  
 
Join Date: May 2011
Location: Canada
Posts: 40
Likes: 0
Received 0 Likes on 0 Posts
I have a long flight ahead of me today.

I'll be back.
VGCM66 is offline  
Old 14th Dec 2011, 15:17
  #643 (permalink)  
 
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 82
Posts: 1,454
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Lyman
@Machinbird. Your cite of PIO is instructive. You neglect another form of out of sync C/R.

Autoflight induced oscillation. AIO
Lyman, I generally disregard your theories since they are normally composed of 2/3 reasonable fact and 1/3 something pulled from behind the refrigerator. My intent in responding is to separate my comments from yours on this occasion.

Judging from where the Autoflight system dropped the aircraft (essentially on altitude, essentially on speed, essentially level) and the fact that the Autoflight system dropped completely out at the cavalry charge, your comment would seem to have no merit. Oscillations generally have a characteristic frequency. What characteristic frequency do you suggest for this phenomena?
Machinbird is offline  
Old 14th Dec 2011, 15:18
  #644 (permalink)  
 
Join Date: Jul 2002
Location: UK
Posts: 3,093
Likes: 0
Received 0 Likes on 0 Posts
Lyman, you're going so far off the deep end by coming up with these ever more elaborate excuses as to how it must have been the aircraft's fault that you have now officially transited the boundaries of known space into la-la land as far as I'm concerned.

You're trying to parlay the autoflight's interrupted response to a comparatively large bump from turbulence - of which not one cycle was completed before the PF took control - into a hitherto-unknown phenomenon that you've just invented. I mean, extrapolation is one thing - but what you're suggesting has not only never been known in the hundreds of thousands of hours the type has been in service, but completely contradicts the evidence at hand.
DozyWannabe is offline  
Old 14th Dec 2011, 16:26
  #645 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 84
Posts: 1,682
Likes: 0
Received 0 Likes on 0 Posts
Lyman,
You repeatedly attribute statements to BEA that I'm unable to find in BEA's publications:
"The aircraft did not immediately respond..." BEA
One needs to take the BEA with generous portions of salt. What about "Rapid Climb", and "the aircraft was not immediately responsive" sounds familiar?
HazelNuts39 is offline  
Old 14th Dec 2011, 16:28
  #646 (permalink)  
 
Join Date: Jan 2005
Location: France
Posts: 2,315
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Lyman
Autoflight induced oscillation. AIO
ROFLMAO....

Thanks for confirming, once more, your total ignorance of basic aircraft stabiliy, and automatic flight control system design and testing.
ChristiaanJ is offline  
Old 14th Dec 2011, 16:44
  #647 (permalink)  
 
Join Date: Oct 2011
Location: invalid value
Posts: 39
Likes: 0
Received 0 Likes on 0 Posts
Quotes supposedly from BEA

I am also curious where those quotes come from. A word search of the BEA reports and press releases reveals no such quotes contained in any of them.
Hamburt Spinkleman is offline  
Old 14th Dec 2011, 23:51
  #648 (permalink)  
 
Join Date: Jul 2009
Location: The land of the Rising Sun
Posts: 187
Likes: 0
Received 0 Likes on 0 Posts
Machinbird
Whilst I do not doubt the phenomenon exists I was reading your post as an indication that you believed the design of the sidestick played a part for inducing the oscillations. This is what I was questioning. All evidence from the Airbuses flying is that the sidestick is a reliable and useful input device with very little in the way of vices. The more I see of the evidence the less it appears that the machine had any role in the accident. There is no 'smoking gun' as it were; just pilots who were not adequately trained or prepared for what should have been a recoverable situation.
Old Carthusian is offline  
Old 15th Dec 2011, 02:14
  #649 (permalink)  
 
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 82
Posts: 1,454
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by OC
Machinbird
Whilst I do not doubt the phenomenon exists I was reading your post as an indication that you believed the design of the sidestick played a part for inducing the oscillations. This is what I was questioning. All evidence from the Airbuses flying is that the sidestick is a reliable and useful input device with very little in the way of vices. The more I see of the evidence the less it appears that the machine had any role in the accident. There is no 'smoking gun' as it were; just pilots who were not adequately trained or prepared for what should have been a recoverable situation.
Let me re-state the theory (And at this point it is just a theory.)
[theory] The AF447 PF made too large of an initial lateral control input and ended up sending the aircraft into a roll oscillation which can be seen in in the BEA charts. He attempted to 'get ahead' of this oscillation by making even more rapid control deflections, but ended up continuing to drive the oscillation. In his frantic attempt to move the stick even more rapidly against the drag of the roll viscous damper, he brought the canted forward stick back from neutral into the nose up direction to obtain better mechanical advantage (since the stick being vertical gives him a greater lever arm). This response would be automatic if he was concentrating on his roll control problem. [/theory]

I agree that the sidestick can be an accurate, useful, and safe means of control. However, the A320 does have occasional problems with roll PIO. Perhaps the A330 does as well in the correct circumstances-like in roll direct mode at altitude.
When a pilot encounters PIO, one of the natural reactions is to believe that the control system is malfunctioning. Most of us would find this extremely disconcerting. It would be good for a double dose of adrenalin. An experienced pilot would change his control strategy to break the oscillation. An inexperienced pilot would likely continue the oscillation until he tired of the effort of driving it. That is what the BEA charts seem to indicate. (And as the roll oscillation began to get under control, so did the nose attitude.)
PIO is a complex condition and should not be blamed on just the sidestick design. If roll PIO was a player in this accident, then the fixes are relatively simple. Roll direct is an infrequent operational mode. Roll direct at altitude will be even scarcer. It is entirely possible that only a small percentage of pilots employ "high gain" control strategies that would trigger a roll PIO. BTW the C-17 aircraft was very late in its development cycle before its roll PIO characteristic was identified and corrected.

Training to avoid "high gain" control strategies would help pilots avoid PIO. Perhaps we need a PIO training device to teach pilots how to avoid it. Meanwhile, "mayonnaise stirring" should definitely be avoided on Airbus type aircraft.
Machinbird is offline  
Old 15th Dec 2011, 09:08
  #650 (permalink)  
 
Join Date: Jul 2009
Location: The land of the Rising Sun
Posts: 187
Likes: 0
Received 0 Likes on 0 Posts
Machinbird
I see what you're driving at now and as a mechanical explanation of the exact process it certainly has merits. However, I suspect that the reaction of the PF would have manifested itself in a similar manner no matter what the input mode. This was not a pilot who was thinking clearly or logically and this was not a crew that was following any known procedure. The proper management of the flight deck was missing and whilst I like the mechanical process you lay out I don't see it as having anything to do with the development of the accident other than the in the most peripheral way.
A330 pilots who have commented on the flight characteristics of the aircraft on these threads indicate that the aircraft is a very stable machine which quickly recovers a stable flight regime even in ALT2. The aircraft seems to be designed to help the pilot as long as the pilot trusts the aircraft.
Old Carthusian is offline  
Old 15th Dec 2011, 12:35
  #651 (permalink)  
 
Join Date: Aug 2009
Location: Texas
Age: 65
Posts: 7,359
Received 551 Likes on 348 Posts
A330 pilots who have commented on the flight characteristics of the aircraft on these threads indicate that the aircraft is a very stable machine which quickly recovers a stable flight regime even in ALT2. The aircraft seems to be designed to help the pilot as long as the pilot trusts the aircraft.
They have also commented upon how challenging hand flying A330 at altitude is.

Machinbird's point on "control strategy" strikes me as well made. His theme takes us back to currency, familiarity, and training in the modes of hand flying a pilot may be exposed to.
Lonewolf_50 is online now  
Old 15th Dec 2011, 14:33
  #652 (permalink)  
 
Join Date: Aug 2011
Location: Grassy Valley
Posts: 2,074
Likes: 0
Received 0 Likes on 0 Posts
For what it may be worth, and I have no illusions, imho, Machinbird is spot on. BEA, having assembled an "HF" group, is attempting to shepherd Opinion in the direction of events that came after the initial blunders, and the aircraft's shortcomings. With a focus on the initial ten seconds and the initial climb, comes widening culpability for the airframer.

BEA quotes: Keep looking, and in their discovery, one may get a picture of how BEA is manipulating the facts.

"ICE, NOT ICE". @Alpha Zulu Romeo. On the contrary, the ICE issue is perhaps the single most important factor in the solution of this mystery.
"ICE", if proven, deflects focus away from the airframe's inabilities to deal with loss of Speeds.

If "NOT ICE", we need to look at AIRBUS' blunders in providing a straightforward solution to Autopilot/Pilot transition, rather than an after the fact publication of accidental and in service mitigations and recoveries. All the defense on this thread of how simples it is to recover an a/c from uncued maneuvering and loss of indications will not hide the fact that there are some obvious and systemic problems with this aircraft.

There is a reason the a/p is disconnected prior to landing, and hazards of airmass therefrom. Generally, the a/p should be disconnected when entering turbulence as well. Better to not let the a/c try to solve something it cannot fix.

Last edited by Lyman; 15th Dec 2011 at 16:09.
Lyman is offline  
Old 15th Dec 2011, 16:38
  #653 (permalink)  
 
Join Date: Jan 2005
Location: France
Posts: 2,315
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Lyman
Generally, the a/p should be disconnected when entering turbulence as well.
Better to not let the a/c try to solve something it cannot fix.
Lieman....,
We got that sorted on Concorde about forty years ago....

ChristiaanJ is offline  
Old 15th Dec 2011, 16:58
  #654 (permalink)  
 
Join Date: Jul 2002
Location: UK
Posts: 3,093
Likes: 0
Received 0 Likes on 0 Posts
@CJ :

No point wasting your breath (or fingers), he's long since stopped taking any notice of anyone saying anything that does not fit his theory, and cherry-picking bits from other posts that he can somehow twist and work in there.

His argument seems to be that there's a massive cover-up going on - to whit, the BEA are steering the outcome to "pilot error" because they aren't taking into account the shortcomings of the aircraft based on a bunch of things he just made up.

(Not to mention ignoring facts like the existence of autoland since the '60s...)

There's no "TURB" switch on the Airbus FBW series autopilot as far as I'm aware, but the established procedure seems to be to engage the "Mach/Speed" mode when encountering turbulence, as it monitors airspeed much more strictly - discussed here:

http://www.pprune.org/tech-log/46809...ence-a320.html

Of course that's not particularly relevant to this case as they had no speed data and thus no A/THR, and even beforehand the thrust remained fairly stable.
DozyWannabe is offline  
Old 15th Dec 2011, 18:23
  #655 (permalink)  
 
Join Date: Oct 2011
Location: Lower Skunk Cabbageland, WA
Age: 74
Posts: 354
Likes: 0
Received 0 Likes on 0 Posts
DW, I too have long-ago lost patience with Lyman's fantasies (quit reading them) BUT!:

I too believe that BEA will make sure that the pilots are blamed. France cannot afford any other outcome. ("Billions and billions.") There is plenty of evidence, though somewhat subject to argument (of course) that there are interface problems with the design, as well as the well-known pitot problem.
Organfreak is offline  
Old 15th Dec 2011, 19:40
  #656 (permalink)  
 
Join Date: Aug 2011
Location: Grassy Valley
Posts: 2,074
Likes: 0
Received 0 Likes on 0 Posts
Gents. From Organfreak, I am reminded of an expression that might apply.

Try not to throw the baby out with the bathwater. BEA have been responsible in the past for rigging the results, and utilizing phony data. For a great deal less than the very existence of AIRBUS, and with it perhaps the economy of FRANCE.

If this turns out to be another "Uncommanded climb", Airbus doesn't have franc one to cover the liability. Let alone the criminal exposure.

Someone ran risk/benefit and figured it was worth the exposure. BEA have shown all manner of unprofessional conduct, flaws in the reporting of their data, and parochial "Memoranda" for mere Market share purpose.

I realize it is difficult to entertain such an accusation, but I believe the truth will out, here, and I believe the Pilots will be exonerated.

Just as you believe your defense of the system is worthy, so do I my challenge of it. I harbor no ill will, and as you will note, I continue to refrain from personal attack. For the simple and exclusionary reason that My respect and admiration for you all runs pretty deep. It does not occur to me to attack, except those I believe are culpable for the tragedy.
Lyman is offline  
Old 15th Dec 2011, 20:07
  #657 (permalink)  
 
Join Date: Jun 2009
Location: Germany
Age: 71
Posts: 776
Received 3 Likes on 1 Post
Turbulence dampening mode

DW
There's no "TURB" switch on the Airbus FBW series autopilot as far as I'm aware, but the established procedure seems to be to engage the "Mach/Speed" mode when encountering turbulence, as it monitors airspeed much more strictly - discussed here:
At least for the A330 / 340 series, which we are discussing here, you are dead wrong.


LHTTM TURBULENCE DAMPING FUNCTION (bolding by me)

General
The purpose of the Turbulence Damping Function implemented in the Electrical
Flight Control System is to damp the structural modes induced by atmospheric
turbulence.

Architecture
The Turbulence Damping Function consists of two lanes:

 Longitudinal lane
The longitudinal Turbulence Damping command is computed by the FCPC1
(FCPC2 as a redundancy) as a function of the Nz accelerometer information.
It is added to the normal law command and transmitted to the
associated elevator servo-controls.

 Rear lateral lane
The rear lateral Turbulence Damping command is computed by the FCPC1
(FCPC3 as a redundancy) as a function of the informationof a specific Ny
accelerometer located at the rear bulkhead level.

It is added to the normal law command and transmitted to the
associated yaw damper.

Specific equipment
The equipment specific to the Turbulence Damping Function are:
- the TURB. DAMP pushbutton switch
- the Ny front accelerometer
- the Ny rear accelerometer.
If not convinced, search for it in this doc Airbus overhead panel description (you have to download the doc) on page 14

system knowledge........?

franzl
RetiredF4 is offline  
Old 15th Dec 2011, 20:13
  #658 (permalink)  
 
Join Date: Dec 2010
Location: Middle America
Age: 84
Posts: 1,167
Likes: 0
Received 0 Likes on 0 Posts
Back To Reality

Lyman

Your Quote:
Generally, the a/p should be disconnected when entering turbulence as well. Better to not let the a/c try to solve something it cannot fix.
Gee, that ought to fix everything when flying at 35K and Mach 0.82

It is getting more bizarre with every post. Here are two quotes that make much sense to me:

1. From Takata Events Leading To LOC (my words)
Illusion, deceleration, and weather.
- Illusion because altitude recorded is "indicated", then partially false at UAS point.
- Deceleration, because autothrust started to reduce N1 by 16% seven seconds before UAS event.
- Weather because there was an up/down/up.
2. From SmilinEd Recovery (my word)
All they needed to do was to:
1. Take a deep breath and watch what the aircraft did under the pitch and power that was set before the AP dropped out.
2. Make gentle corrections to ensure that altitude and heading were maintained within some reasonable limits given the turbulence encountered.
They didn't do either.

Further, Why did they get to where they got to when all this happened (A/P disconnect, A/T disconnect, etc.)? Why did they think the ITCZ was somewhere off in the distance and may have been surprised to find themselves in the middle of it? What were the cockpit conversations, P/F P/NF, not just 5 or 10 minutes before A/P disconnect, but 30 minutes before? Who was monitoring the weather radar? Was it being monitored? Was it set properly? IMHO, this is where the setup to disaster began, but not much has been said about this.

TD
Turbine D is offline  
Old 15th Dec 2011, 20:36
  #659 (permalink)  
 
Join Date: Aug 2011
Location: Grassy Valley
Posts: 2,074
Likes: 0
Received 0 Likes on 0 Posts
TurbineD

With utmost respect, take a breath and consider how well both takata and Smilin Ed fold in with my projection of UPSET prior to UAS. A/T was reducing N1 due a severe Updraft, and combined it with a NOSE DOWN input additive. (takata/BEA) And the a/c lost 380 feet. ACARS shows a WINDSHEAR event early on, along with TCAS warn due exit of altitude approved.

Ed is a bit more complex, since the a/c ostensibly, with Inertial recovered data, showed a PITCH resting on 0, (Three degrees+ LOW), and power that was set correctly for an airmass that was markedly different in two seconds from what was indicated and what he felt. In short, the system was dynamic, the AoA was nine degrees delta PITCH, and power was at ~73? STALLSTALL. Sound familiar? This behaviour was patent on other 330's and at least one 340 prior to 447. One cannot with confidence refuse to review patent behaviour in this accident. BEA would have it, and as you know, I trust BEA to be true to BEA past performance.

The past will repeat, especially when there is no incentive to alter the march of the chariots. The aircraft is a long and heavy tube. Which accelerometer was which, again?
Lyman is offline  
Old 15th Dec 2011, 21:27
  #660 (permalink)  
 
Join Date: Oct 2011
Location: invalid value
Posts: 39
Likes: 0
Received 0 Likes on 0 Posts
The Turbulence Damping Function is part of the Flight Control System and not the Auto Flight System. It is normally on and not dependant on an AP being engaged.

There is no autopilot turbulence mode and the Turbulence Damping Function is somewhat different from the TURB autopilot mode of previous non-FBW Airbus. That would disengage pitch mode which would revert to pitch hold while the lateral mode would be retained and THS trim speed reduced.
Hamburt Spinkleman 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.