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AF447

Old 18th Dec 2009, 05:14
  #4561 (permalink)  
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Rotation isn't required for a flat spin.

Now, that's something I've never considered. Perhaps you can cite some references for my study ?
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Old 18th Dec 2009, 06:45
  #4562 (permalink)  
 
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John: You missed your vocation, you should have been a diplomat.
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Old 18th Dec 2009, 10:47
  #4563 (permalink)  
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You missed your vocation

.. I always try to be circumspect .. on far too many occasions over the years, after shooting off my mouth .. I have had to eat umble pie when I find that I was wrong ... as they say "often it is better to keep one's peace and forever be thought a fool ... than to open one's mouth and remove all doubt ... "

Graybeard's commentaries generally run to wisdom .. so I prefer to seek his guidance .. I may well learn something useful along the way.
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Old 18th Dec 2009, 11:51
  #4564 (permalink)  
 
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Short summary of the new BEA interim report

Hi there,
Here is a short summary of the report:
-From the visual inspection of the varied debris (toilet doors, partitions, galleys, cabin crew rest module, spoiler, aileron, vertical stabiliser):
The aircraft was probably intact on impact.
The aircraft struck the surface of the water with a positive attitude, a low bank and a high rate of descent.
There was no depressurisation
The report does not put forward any descent rate, deceleration figure (except the 36 g /120 000 N for the VS) or other figures resulting for exemple from an accurate metallographic analysis of well chosen debris.

-The medical and pathological Information drawn from the autopsy reports does not add so much, and does not enable to know whether the Captain was in the flight deck at the time of the crash.

-The ACARS analysis is refined, 21 of the 24 can be related to a failure of the anemometric loop, at least one more ACARS message (a class 2 fault message about the ADR2) should have been transmitted between the last ACARS (02:14:26Z) and 02:15:14Z.

-The meteorological analysis is slightly refined (surface to mid altitude convection cells using the Tropical Rainfall Measuring Mission / Cloudsat data): it suggests the presence of strong condensation towards AF447’s flight level (10 000 m) probably associated with convection towers.

-The BEA studied thirteen events on Airbus A330 / A340, losses of or temporary anomalies in indicated speeds occurring for which it had both crew reports, parameter recordings the PFR: Air France (4 cases); TAM (2 cases); Qatar Airways (4 cases); Northwest (1 case); Air Caraïbes Atlantique (2 cases).
It can be noted from this analysis that:
In seven cases, the autopilot was reconnected during the event. In two of them, the re-connection occurred when the two speeds were consistent with each other but were erroneous;
The autothrust disconnected in ten cases, leading to the activation of the Thrust Lock function. In five of them, this function remained connected for over one minute;
In 2 cases, the autothrust did not disconnect and the flight directors did not disappear. The recording of the engine RPM parameters shows fluctuations in thrust with N1 values of between 48% & 100% ;
Nine cases of triggering of the stall warning were observed.
With regard to crew reactions, the following points are notable:
Five cases of a voluntary descent were observed, of which one was of 3,500 feet. These descents followed a stall warning;
Four crews did not identify an unreliable airspeed situation.
The duration of the engagement of the Thrust Lock function indicates that there was no rapid autothrust disconnection actions then manual adjustment on the thrust to the recommended thrust;

To explain the exiting of the flight enveloppe, the BEA thinks to the risk of an attitude/thrust mismatch, when the A/THR disconnection occurs with a low N1 value. Woudn't the greatest danger be when the A/THR goes off with a high N1 index (or full thrust), this being maintained "several dozens seconds" or "over a minute", the plane being put in descent following a stall warning ?
Jeff
PS) Nowhere in the report, it is said that the false alarms may have played a major role in the accident but in a paragraph about "Operator training for the Unreliable IAS / ADR check emergency / backup procedure", it is concluded that the key points for a correct management of the situation are: detection of the problems, interpretation of the alarms and coordination in processing.

Last edited by Hyperveloce; 18th Dec 2009 at 11:57. Reason: text reformatting
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Old 18th Dec 2009, 21:19
  #4565 (permalink)  
 
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BEA Report - Crash Position??

The Annex to the report outlines the difficulties that the various organisations participating in the phase 1 and 2 searches had in backtracking the drift (set & leeway) for the Vertical Stabilizer. As I have indicated in previous posts, the onset of the North Atlantic Equatorial Counter Current in the suspected crash area has had a major bearing on the position from where the surface debris may have originated.

Notwithstanding, the following organisations calculated debris positions:-
Météo France, Brazilian Meteorological Service, US Navy, and US Coast Guard.

No methodology has been revealed (except that computer modeling was used), but there is obviously major differences in the vectors used. From the BEA report I have reproduced a chart showing the calculated positions, and have overlaid it with data I previously posted to this forum http://www.pprune.org/5216571-post4476.html

Data in red or yellow has been added by me.



Mine and the Météo France positions are further to the west than the others and outside the prime area of interest. There is 89NM between the most eastern and western positions, but only 7NM in the north / south distribution. An initial investigation was made in the area of the Météo France position to remove any doubts, and the current concentration is centered on 3°10'N 30°25W.

Time will of course reveal how valid any of the positions are.

mm43

Last edited by mm43; 19th Dec 2009 at 19:28.
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Old 18th Dec 2009, 21:58
  #4566 (permalink)  
 
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Rotation isn't required for a flat spin.
Isn't a flat spin without the spinning called a "deep stall"? (Elevator as well as wing are stalled?)
Whereas a normal spin has the spinning in addition to the stalled wing of the stall?
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Old 19th Dec 2009, 02:44
  #4567 (permalink)  
 
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john tullamarine

Cannot accept that an aircraft can spin without spin. Let's call it a deep stall instead.

Know of several deep stall losses in the UK during which many attempts were made to recover. Ossie Hawkins couldn't recover a Vulcan even after releasing the braking parachute. He survived the ejection.

John Baker did recover a HP Victor using the braking chute which was torn off in the process. He had entered a deep stall and some spinning after losing airspeed reference.
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Old 19th Dec 2009, 09:27
  #4568 (permalink)  
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Cannot accept that an aircraft can spin without spin

That has been my conventional understanding .. that a spin is an autorotating stalled mode of flight.

However, I am always open to new ideas ..

Planning to be driving through Canberra mid next week .. are you about for a coffee ?
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Old 20th Dec 2009, 03:07
  #4569 (permalink)  
 
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A translated portion of the Annex

1.3 Reverse drift calculations

The knowledge of currents and winds in the area of the accident can provide a theoretical estimate of the previous positions of each body and debris identified by calculating a trajectory in reverse. An estimate of a possible impact zone at the time of the accident on 1 June 2009 at about 2 h 15 UTC, can be had by taking this route. This calculation is called retro-drift or reverse drift.

A team of experts from Météo-France, SHOM, IFREMER, Mercator Ocean and CROSS Gris-Nez worked on the calculations of drift. The U.S. Navy, Brazilian Navy and U.S. Coast Guard (USCG) also provided the results of their calculations.

The different points of retro-drift were calculated from the positions of Debris and bodies found on 6 and 7 June, and especially from the position of the vertical stabilizer found on 7 June 2009.

Calculations by the USCG for an estimated position of the vertical stabilizer on 1 June at 2 h 15 placed it at 30 NM south-east of its position on 7 June. Furthermore, an estimated position for the bodies on 1 June was also calculated, assuming that they drifted to the surface from the scene of the accident.

Calculations by the Brazilian Meteorological Service and the U.S. NAVY results approximate the USCG position. These simulations used the same NCOM model (1), and the results are in the Alpha area that was explored by TPLs (US Navy's Towed Pinger Locators).

Calculated retro-drift of the vertical stabilizer made by Météo - France has in turn provided an estimated impact position on 1 June at 2 h 15 approximately 50NM to the south-west of its position on 7 June. This zone extends about 25NM depending on an assumed vertical immersion of the tail of between 80 and 100%. These results differ from those provided by other simulations of backward drift.

Calculations by Météo France were based in particular on the current model developed by Mercator (2). As the results from Météo France were in a relatively remote part of the Alpha area, this area to the west was explored by the SNA (Nuclear Attack Submarine "Emerald") with the main objective to remove any doubts.
(1) NCOM model (Navy Coastal Ocean Model) is based on a 1/8° resolution grid (ie approximately 15 km). It is fed by the Air NOGAPS model (resolution 50 km) and receives daily U.S. Navy Data observations and data forecasts at hourly intervals. This data is regularly assimilated and compared internally, along with data returned by drift buoys.
(2) The Mercator model comprises two sub models, PSY2 and PSY3. - Mercator PSY2 is an Atlantic and Mediterranean High resolution model on a 1/12° (or 9 km) grid and with fifty vertical levels. The surface wind model is the ECMWF (European Center for Medium - Range Weather Forecasts) at 25 km resolution. It produces current fields daily. - Mercator PSY3 gives an over all Oceans average resolution of 1/4°, i.e. approximately a 25 km grid.
I'll try and translate other parts of the Annex when I get time.



I created the graphic above last August to give a general idea of how the currents were behaving at the time of the crash. The reverse drift positions for the vertical stabilizer provided in the BEA Interim Report No.2 have been added in magenta.

mm43

Last edited by mm43; 21st Dec 2009 at 17:12. Reason: expanded some acronyms, i.e. SNA and TPL
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Old 21st Dec 2009, 05:02
  #4570 (permalink)  
 
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Just curious - if the tail failed, why no messages of hydraulic low system pressure (any system) or control faults?

ECAM Actions.
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Old 21st Dec 2009, 08:25
  #4571 (permalink)  
 
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Perhaps it failed after the aircraft attempted to become a submarine regardless of the crew's intentions?

Seriously, the failure mode for the tail is not possible to create in the air unless God reached down and swatted it on the nose. It can fail in that mode upon hitting the water with some forward motion and a pretty stiff downward motion. By then the plane is breaking up very rapidly and no more messages of any kind are leaving the debris field.

{o.o}
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Old 22nd Dec 2009, 00:39
  #4572 (permalink)  
 
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What a perplexing case to unravel. Would anyone care to postulate any assumptions on the missing 'MAINTENANCE STATUS ADR2' message that not been transmitted, on a plane that:

1. Was assumed (by the BEA report) to have full hull integrity, until it hit the water.
2. Remained in a 'pitch-up (attitude), with a slight bank and at a high vertical speed'


With possible non-transmission of this message, put down to (copied from the report):

'loss of one or more system(s) essential for the generation and routing of
messages in the aircraft:



ATSU / SDU / antenna: none of the maintenance messages sent is
related in any way whatsoever with the functioning of these systems. A
malfunction of this type should have occurred after the transmission of
the last message and without forewarning.


loss of electrical power supply: this would imply the simultaneous loss of
the two main sources of electrical power generation.


loss of satellite communication:


loss of data during transmission: the satellite’s quality follow-up does
not show any malfunction in the time slot concerned.


loss of contact between the aircraft and the satellite:


unusual attitudes: given the relative position of the satellite with respect
to the aircraft and the aircraft’s tracking capability, the antenna would
have to be masked by the aircraft’s fuselage or wings. Examination of
the debris showed that the aircraft hit the water with a bank angle close
to zero and a positive pitch angle. The aircraft would therefore have
been able, in the last seconds at least, to transmit an ACARS message.
end of the flight between 2 h 14 min 26 and 2 h 15 min 14.'

BEA also noted that the flaps were retracted on track 3 upon impact. This states in my mind that the flaps were retracted at some stage by the crew, or forced there by aerodynamic loads - with the former being highly likely. If that was the case, the crew had time to retract the flaps, in plane that at some point before the blue stuff, was relatively flat, with ACARS working until a certain point. I cannot believe a plane that was maybe (please dont kill me, it is a basic assumption from the scant evidence given) in a stall scenario, did not have time to electronically send a message? (unless a complete power loss was present)...

UM

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Old 22nd Dec 2009, 01:01
  #4573 (permalink)  
 
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@UM
end of the flight between 2 h 14 min 26 and 2 h 15 min 14

The 2:14:26 time was the aircraft / satellite handshake time of the last message transmitted and received in Paris. The 2:15:14 time was the latest time that the fault message believed to be in the system would have been sent and received.

There may have been other ACARS messages waiting for transmission, but we do not know. I suspect the actual impact time was seconds after the handshake time at 2:14:26.

mm43
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Old 22nd Dec 2009, 01:18
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Thank you and agreed. Assuming that the FCPC1 (PRIM 1) message was picked up at 2h 13min 45 (assuming a 1 min transmission for the fault message), then i reckon the impact time was in between 2h 14 min 26 - 2h 14 min 45.

UM
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Old 22nd Dec 2009, 12:43
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Question Questions on Stall Warning threshold calculation

The BEA 2nd Interim Report describes the calculation of the Stall Warning threshold as follows (in paragraph 1.6.11.4 on page 46, english version):
In alternate or direct law, the angle-of-attack protections are no longer
available but a stall warning is triggered when the greatest of the valid angle-of
-attack values exceeds a certain threshold. In clean configuration, this threshold
depends,in particular, on the Mach value in such a way that it decreases when the
Mach increases. It is the highest of the valid Mach values that is used to
determine the threshold. If none of the three Mach values is valid, a Mach value
close to zero is used. For example, it is of the order of 10° at Mach 0.3 and of 4°
at Mach 0.8.
This information leaves me with several questions -

Firstly, the Stall Warning should occur when the AOA exceeds 4 deg at Mach=0.8, but does not occur until AOA exceeds 10 deg when airspeed is invalid. In that case, is the Stall Warning still timely enough to permit the pilot to avoid stalling?

Secondly, in the Air Caraibes incident in october 2008 Stall Warning occurred at AOAs of 4.48 deg and 4.31 deg, while the calculated threshold was 4.2 deg. This would correspond to the actual Machnunber around 0.8, but how could 0.8 have been the 'valid' Machnumber for the system while both PFDs were displaying Mach=0.3, in ALTERNATE law, ADR DISAGREE, FD 1&2 lost, etc.?

Finally, the A330 FCOM procedure UNRELIABLE SPEED INDICATION / ADR CHECK PROC states:
Rely on the stall warning that could be triggered in alternate or direct
law. It is not affected by unreliable speeds, because it is based on angle of
attack.
Was the author of this procedure unaware of how the system works as described by BEA?

Regards,
HN39
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Old 23rd Dec 2009, 19:43
  #4576 (permalink)  
 
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@HN39
Was the author of this procedure unaware of how the system works as described by BEA?
The BEA version and the A330 FCOM procedure do seem to be in conflict.

Perhaps an email to BEA with a CC to Airbus may result in a clarification

mm43
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Old 24th Dec 2009, 12:34
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Stall warnings threshold

Hi there,
I have just emailed to the BEA to ask further informations about the stall warnings triggering conditions (and more precisely how the Air Caraïbe incidents could have generated stall warnings if we follow the principles described in the 2nd BEA report).
Low probability to get an answer but...
Merry Christmas to all of you

Jeff
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Old 24th Dec 2009, 20:20
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Angel A Happy Airbus

Thanks Hyper.

Hopefully other operators and jurisdictions will have noted the anomaly and queried the BEA and Airbus.

Merry Christmas

mm43
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Old 24th Dec 2009, 20:48
  #4579 (permalink)  
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Stall warnings with UAS.

This revisits the Qantas flight, and Stall warning confusion. Has a paper re: unreliable Stall warning been issued by AB? BEA?
 
Old 26th Dec 2009, 13:16
  #4580 (permalink)  
 
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this crash is really frustrating. god knows what happened to the plane
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