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

AF 447 Search to resume

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

AF 447 Search to resume

Old 9th May 2010, 08:11
  #921 (permalink)  
PJ2
 
Join Date: Mar 2003
Location: BC
Age: 72
Posts: 2,452
Takata;
Consequently, variations of measured pressure are assumed to be the cause of cabin regulation issue. My opinion is that those variations are not the result of actual (real) pression difference. All systems that are going off, including this one, are feeded by unreliable informations comming from frozen probes.
For my understanding of your views and given this statement, are you claiming that the static ports were also iced?

HN39, just read from the FCOM, the cabin altitude is limited to 7350' for flights over 2hrs; under 2 hrs it goes to 8000'.

PJ2
PJ2 is offline  
Old 9th May 2010, 09:14
  #922 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 81
Posts: 1,689
Cabin V/S Advisory

takata,

thank you for your elaborate reply. Let me first clear up a possible misunderstanding. I'm not ignoring the ICE issue. At the origin of the ACARS messages is an airspeed 'discrepancy'. The only and almost universally accepted explanation for that is blockage of the pitot tubes by icing.

However, cabin pressure is not affected in any way by pitot pressures. The cabin pressuration systems uses aircraft altitude, which is derived from the pressure measured at the static ports. These are flush with the skin, and do not collect ice in the way that the pitots do. Nothing in the ACARS messages indicates a problem with the static pressure. The pressure measured at the static port is normally corrected for 'position error'. BEA's 2nd interim report explains that this correction is not correctly applied when airspeed is corrupted. However, the resulting error in the indicated altitude is so small (300 ft) that it does not in itself cause a problem with any system.

Originally Posted by takata;#918
Right, but what it means is that pressure varied, no more.
Here I respectfully disagree. The message means that at this point the airplane was below 7350 ft, descending rapidly, and at least one engine was operating.

If total engine failure occurred, it must have occurred between 2:14:26 and 2:15:14, below 7350 ft, at temperatures above freezing.

HN39

EDIT:: 8000 ft changed to 7350 ft. My thanks to PJ2 for info in #920. I don't have access to the FCOM.

EDIT 2:: Further to my post #909, some selected quotes from the applicable regulations:
§ 25.841 Pressurized cabins.

(a) Pressurized cabins and compartments to be occupied must be equipped to provide a cabin pressure altitude of not more than 8,000 feet at the maximum operating altitude of the airplane under normal operating conditions.

(...)

(b) Pressurized cabins must have at least the following valves, controls, and indicators for controlling cabin pressure:

(1) (...)

(2) Two reverse pressure differential relief valves (or their equivalents) to automatically prevent a negative pressure differential that would damage the structure. One valve is enough, however, if it is of a design that reasonably precludes its malfunctioning.

(3) A means by which the pressure differential can be rapidly equalized.
EDIT 3:: "less than 50 ft" corrected to 300 ft

Last edited by HazelNuts39; 9th May 2010 at 11:59. Reason: as indicated
HazelNuts39 is offline  
Old 9th May 2010, 09:33
  #923 (permalink)  
 
Join Date: May 2010
Location: PLanet Earth
Posts: 821
I've been following this Thread and its predecessor closely from first post on.
@mm43:
When I look at the likely crash location you determined last September and comparing it to the location they are now searching in detail it is absolutely striking how good that matches !!!

It seems your research bettered all the experts of BEA and those directly involved in the Search. Amazing !
Maybe they should have listened more to PPRuNe and especially to you!

What remains a bit of a mystery to me is how they could have come that far from the last known position and hit the surface with very little forward speed. And all that after a hard 180° turn.
Normally such a hard turn would cause speed bleed.

If you calculate the time/distance between last known position and actual search location this would require ~ 500kts average speed point to point even without considering turn (speed loss and longer actual flight path) and deep stall (forward airspeed <<100 kts).
Maybe there is indeed some merit to the flameout scenario...
henra is offline  
Old 9th May 2010, 11:11
  #924 (permalink)  
 
Join Date: Jun 2009
Location: Paris
Posts: 691
Hi HazelNuts39,
Originally Posted by HazelNuts39
thank you for your elaborate reply. Let me first clear up a possible misunderstanding. I'm not ignoring the ICE issue. At the origin of the ACARS messages is an airspeed 'discrepancy'. The only and almost universally accepted explanation for that is blockage of the pitot tubes by icing.
However, cabin pressure is not affected in any way by pitot pressures. The cabin pressuration systems uses aircraft altitude, which is derived from the pressure measured at the static ports. These are flush with the skin, and do not collect ice in the way that the pitots do. Nothing in the ACARS messages indicates a problem with the static pressure. The pressure measured at the static port is normally corrected for 'position error'. BEA's 2nd interim report explains that this correction is not correctly applied when airspeed is corrupted. However, the resulting error in the indicated altitude is so small (less than 50 ft) that it does not in itself cause a problem with any system.
Well, I know that static ports are not supposed to fail... but, directly from AIRBUS specifications, in case of UNRELIABLE AIRSPEED (caused by Pitots failure) SPEED as well as ALTITUDE are both to be considered unreliable. Check it yourself!
Furthermore, I studied last summer the various UNRELIABLE AIRSPEED events reports, and in several cases lasting for more than few seconds ALTITUDE was also directly affected (if I remember correctly, during Air Caraibes event, variations were in the range of 300 ft). Which point to the fact that whatever pressure could be "correctly" measured by static ports, Pitots failure would affect the data processing.
This may be due to ADIRUs, as I think that total pressure is used to correct static pressure at some point during the process. But the question is what data will then be used to supply the CABIN pressure controler when all ADIRUs are rejected or turned off-line ?

Originally Posted by HazelNuts39
Right, but what it means is that pressure varied, no more.
Here I respectfully disagree. The message means that at this point the airplane was below 8000 ft, descending rapidly, and at least one engine was operating.
If total engine failure occurred, it must have occurred between 2:14:26 and 2:15:14, below 8000 ft, at temperatures above freezing.
May I respectfully ask: how are you jumping to this somewhat dodgy conclusion?
S~
Olivier
takata is offline  
Old 9th May 2010, 12:07
  #925 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 81
Posts: 1,689
Cabin V/S Advisory

Originally Posted by takata;#923
during Air Caraibes event, variations were in the range of 300 ft).
Hi takata;
you are quite correct. "less than 50 ft" should read 300 ft. BEA's analysis shows the same value.

HN39

EDIT:: In the Air Caraibes case, or any other reported UAS event, there is no mention of a cabin v/s advisory.

Last edited by HazelNuts39; 9th May 2010 at 12:25. Reason: as indicated
HazelNuts39 is offline  
Old 9th May 2010, 13:38
  #926 (permalink)  
 
Join Date: Jun 2009
Location: in a plasma cocoon
Age: 50
Posts: 244
Hi there.
@02:10Z, the crew is submerged by alarms & ECAM messages, possibly false alarms (those are not transmitted in the ACARS) like in the other past cases of Pitot failures (stall alarms most of the time, overspeed alarms occasionally), airspeeds are unreliable, no more A/P or A/T, alternate mode 2 (loss of many flight protections), no visual clues (night with bad visibility), possibly turbulent atmosphere... and lengthy/tricky procedures to implement... The anemometric failure is detected @02:10 but the failure of the 3 anemometric chains may have begun some tens of seconds before, beginning with the exclusion of a 1st ADIRU against the two others (which may have diverged in a similar/agreement fashion) ending with the disagreement between the two ADIRU remaining.
Some others have pointed out the plausibility of a crew rotation just before (@02:00Z), CPT going to rest.
At this point (@02:10-02:11), taking in account the large route variation of the AF447, wouldn't the worrying possibilities be: a bad reaction of automation (A/P) to the erroneous airspeeds before their unreliability can be detected (for example A/P & A/THR OFF with TOGA LK which would remain locked: overspeed risk) and/or drifts induced by A/P OFF (a growing bank angle, since the automation did not control it any longer), and/or the risk of overloaded attentions of the crew, stretched between procedures implementation and manual flight: as I see it, a first risk would be to badly react to a false stall alarm (frequent) meaning taking it for real and following the procedures accordingly (risk of overspeed), another risk would be not to pay attention to the growing bank angle, and let it drift in excess (say over 60°-70°) before trying to regain control. The high altitude overspeed/mach buffet has been somewhat debated on PPRuNe, the other is similar to the Adams Air case (but less extreme: for AF 447 the roll would be controlled and the control of altitude close to be regained). Maybe there are other early (@02:10-02:11Z) risks in the chain of events ?
We now know that the crash area could be such that it imply a large route deviation (more than 135°), and a rapid descent (35000 ft over 40-50NM in less than 4mn45sec: -9° of average slope or ~7500 fpm in average). Beyond the high altitude stall/mach buffet, there are also the fully developped flat spin hypothesis, and the engine flame out. Apart the high altitude mach buffet or stall, could the terminal trajectory be explainable by a large initial roll/bank perturbation in cruise at high altitude like the Adam Air ? (possible causes: bank drift that remains unoticed due to task overload & spatial disorientation, only a wing stalls in overspeed, turbulences,...). The time needed to control the large initial bank perturbation would induce a large route deviation and loss of altitude. Maybe also that attempting to control the altitude before having controlled the excess of bank angle would be a bad reaction and would worsen the situation (Adams Air case I think). The terminal conditions described by the BEA reports (A/C en ligne de vol so 0° roll/bank, nose up/tail impact first, vertical compression) suggest that, in the vertical plane, there may have been a rapid loss of altitude initially (much larger than the average 7500 fpm, combined with the large roll pertubation, to control first) followed by a ressource (route stabilized toward E-34) in an attempt to control the altitude, close to its lowest point (vertical speed much lower than the average 7500 fpm), with an incidence (nose up) at the impact/pancacking with the surface. I think that the trajectory would pretty much look (horizontally) like the MM43's illustration (a blunt/short radius turn (with a rapid loss of altitude) and a rectilinear end (which would be the ressource attempt).
Jeff
Adams Air case: Aircraft Accident Report AdamAir PK-KKW (see page 28, the bank angle exceeded 90°, the variations of altitude -35000 ft & route: +250° in ~1min)
Hyperveloce is offline  
Old 9th May 2010, 16:07
  #927 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 81
Posts: 1,689
Scenario

RE: mm43 #911

mm43;
I concur with your trajectory and events, except no.5: -
If the cabin v/s condition followed engine flameout, the corresponding ACARS message would not have been sent. In my opinion flameout is a dispensable element in this chain of events.

regards,
HN39
HazelNuts39 is offline  
Old 9th May 2010, 16:33
  #928 (permalink)  
 
Join Date: Jan 2008
Location: Herts, UK
Posts: 743
Yes, flameout optional and not yet a given requirement, but possible?
But an excellent overall synopsis agreeing that a deteriorating lateral stability situation could have played a major part, particularly in an early and rapid course change... one also wonders whether we should postulate that the shorn-off spoilers as consequence of airborne rather than impact related stresses...

I do hope contributors will avoid trying to connect (tie-together) the actual BEA sea-surface impact conclusions with the prior (LOC) trajectory.. there is really no need to assume that partial or full control was not regained prior to impact (i.e. that flight problems at cruise can be realted to impact attitude/speed). There are many other ways the descent and the actual crash into the sea could have been connected together, without one continuous event, surely?

Also still reminding myself that this was a terrifying few minutes for so many on board and a very bad night for civil aviation generally... many lessons must be learned, and as usual, no doubt it will be found that so many should have been learnt before and lessons implemented properly so many years ago - I am sure that 'basics' are involved here that people died for long ago!

Last edited by HarryMann; 9th May 2010 at 18:42.
HarryMann is offline  
Old 9th May 2010, 16:35
  #929 (permalink)  
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 77
Posts: 1,330
originally posted by HazelNuts39.....
If the cabin v/s condition followed engine flameout, the corresponding ACARS message would not have been sent. In my opinion flameout is a dispensable element in this chain of events.
Somewhere in one of the AF447 threads, I tried to explain away the SATCOM loss of signal, and came to the conclusion that there had been a 2 x flameout. However, I am open to other opinion, and the resumption of the SATCOM link could also be explained by the APU having been started, or a start achieved on #1. The BEA's comment regarding the tail rotating to port on impact could be related to the wings level, small positive attitude and TOGA on #1 with the RTLU locked at 7.9 degrees.

If the APU had been started, would the Cabin Pressure controller have been active? I haven't seen any data on this, and have assumed that should there be no electrical supply from the prime sources that the controller would operate below 8000/7350 feet to equalize the cabin pressure.

mm43
mm43 is offline  
Old 9th May 2010, 17:01
  #930 (permalink)  
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 77
Posts: 1,330
The vessel appears to be operating in a fairly confined area, and my suspicion is that the ROV is being used at the following location:-

8 May 2010 23:18z Hdg 157.5 Spd 00.5 2°42'04"N 31°13'39"W

Refer to Post #904 for the supporting graphic.

mm43
mm43 is offline  
Old 9th May 2010, 17:43
  #931 (permalink)  
 
Join Date: Jun 2009
Location: I am where I am and that's all where I am.
Posts: 660
mm43, in your graphic showing the 50 degree bank how does the time for that event compare with the loss of signal period for the ACARS data? (Sorry, I don't have the BEA report at my fingertips. I do note a sudden 50 degree bank would move the ACARS antenna off the satellite during the event. It likely would not be able to reestablish it for the turn shown until the plane leveled out again.)

{^_^}
JD-EE is offline  
Old 9th May 2010, 17:48
  #932 (permalink)  
 
Join Date: Jun 2009
Location: Chesapeake Bay
Age: 76
Posts: 57
Google Earth .KMZ Overlay

With the hope that a summary of known positions placed into 3D space in Google Earth might be of help, I have built a .KMZ file containing the known track of the aircraft drawn at altitude FL350 (10668 meters) and the location of the search vessel SEABED WORKER on May 8, 2010 placed at sea level. Concentric rings at 10 nautical mile increments radiate from the Last Known Position of AF447 at 0210. The area of interest (Seabed Worker) is 42.11 NM, heading 246.20 deg., from the Last Known Position. For reference, I included the excellent, if not stunning, chart by mm43 created April 2, 2010 and posted to PPRuNe (#650), scaled and overlaid onto the ocean surface:



Download the Google Earth .KMZ file here. [720KB]

Load the .KMZ file into Google Earth (Version 5). Use the Places Panel to check or uncheck the visibility of various layers:



I will update this .KMZ file with new information after the BEA press conference tomorrow.

Good luck to all!

GB

Last edited by GreatBear; 11th May 2010 at 06:18. Reason: Updated Links
GreatBear is offline  
Old 9th May 2010, 18:01
  #933 (permalink)  
 
Join Date: Jan 2010
Location: EU
Age: 50
Posts: 251
Thanks to all and specially 'mm43' for this very interesting thread. Here goes with a very small contribution.
Day before yesterday there was an interesting article in the Spanish press, namely the 'El Pais' newspaper. Just like many other newspapers they have also used the word 'located' in their headline, which raised my hopes that the 'black boxes' had been found but the article nonetheless offers other news that has not appeared in previous posts, so here goes with a translation:

Air France Rio-Paris airplane black boxes located
The black boxes of the Airbus flying from Rio de Janeiro with destination Paris belonging to the company Air France have been located nearly a year after the accident, when it crashed into the Atlantic on 1 June with 228 persons on board. They are to be found, according to the French Ministry of Defence, somewhere at a depth of 3,000 metres in an area of about 100 square kilometres at about 1,000 kilometres from the Brasilian coast. It will not be easy to find them. "It will be like looking for a shoe box in an area as big as Paris and with a mountainous area similar to the alps." said the French Navy Spokesman, Hurgues du Plessis. The find had been given up as lost, since the black boxes only had batteries that lasted two months to emit a signal in order to be located. The delimitation of the area has come about thanks to the investigators who have newly examined the recordings of a submarine that weeks after the accident combed the area blindly (blindly=randomly?)and at the time no signals were detected. Thanks to software developed by the industrial group THALES, it has been possible to isolate the toc-toc-toc signals from the boxes. But that sound no longer exists that would serve as a guide and finding the boxes will be a miracle.
The causes of the accident are still unknown. The official French organisation in charge of the investigation maintains that the aircraft crashed into the sea and that it did not disintigrate in the air, and that Pitot tubes, curiously also manufactured by the THALES group, that measured it's speed were giving contradictory inputs. This was one of the causes for the accident. But on its own would not explain the reasons for the accident.

First, it is difficult to imagine that a highly sofisticated and modern nuclear submarine would miss 'hearing' the signals from the black boxes but much more so to accept, that while they were recording sound, they did not record their position relative to the sound recording. Perhaps they did and for military reasons this information has been restricted. If then there is a record of the submarine's position that can be related to the sound recording, then finding the boxes becomes a real possibility in a fairly short space of time and perhaps the reason why the "Seabed Worker" is maintaining a position in a limited area, according to "mm43".
The other interesting bit of news is that the pitot tube manufacturers THALES are actively assisting in the search and developed the software to 'clean' the submarine's sound recordings and be able to identify the signals from the black boxes. Obviously THALES have an interest in finding the black boxes which might assist in establishing to what extent the pitot tubes were to blame for the accident and if there were other factors that contributed to the crash.
DjerbaDevil is offline  
Old 9th May 2010, 18:02
  #934 (permalink)  
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 77
Posts: 1,330
JD-EE; 2:13:08 was ground station receipt time = 2:13:10 on handshake, and 2:13:45 is ground station receipt of next message = 2:13:41 on initiation. Known LOS equals 31 seconds. They were in low latitudes (3N) and a 50 degree bank when using the 6dB omni shouldn't have caused a drop-out. I believe the SAT was about 15 degrees east of them.

mm43
mm43 is offline  
Old 9th May 2010, 18:57
  #935 (permalink)  
 
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 78
Posts: 1,459
Hi MM43. One way to achieve a tight ground referenced turn radius is to accomplish the majority of the turn in the vertical. This may be indicative of a LOC incident early on.
Gimbal angle limits on a satellite antenna could well explain a drop out, but the satellite data drop out seems to be much later than the initial deviation, so perhaps a second unusual attitude at that time??? I'm still trying to make some sense of the information at hand without too much luck.

Last edited by Machinbird; 10th May 2010 at 02:21.
Machinbird is offline  
Old 9th May 2010, 19:01
  #936 (permalink)  
 
Join Date: Dec 2005
Location: Finland
Posts: 242
Tracer buoys?

The charts by mm43 and greatbear made me think about the role of the currents transporting debris from the impact point.

What if the first search planes on scene would as a standard practice drop, say, twenty tracer buoys (with GPS and a location transmitter) over the search area in order to map out the surface currents as accurately as possible? Then when debris is subsequently found, this "current map" would enable much more accurate pinpointing of the actual impact point.

What do you think, would this be a) useful, b) feasible for future similar crashes ? According to Wikipedia, a Brazilian SAR aircraft spotted debris about 35 hours after the crash. It is not clear if there were other search aircraft in the area before, but even so I'd assume that the more accurate picture is collected about the surface currents, the bigger likelihood of locating the wreckage.

PS: Sorry if this has been mentioned before... I had no time to scan the large number of previous messages.
snowfalcon2 is offline  
Old 9th May 2010, 19:42
  #937 (permalink)  
 
Join Date: Jul 2009
Location: France - mostly
Age: 81
Posts: 1,689
High speed impact???

Looking in BEA's reports for information on the forward speed at impact, the closest thing I was able to locate is based on detail examination of fuselage frame segments attached to the base of the vertical stabilizer, from page 28 of BEA's 2nd Interim Report:
The deformations of the frames were probably the consequence of the water
braking the aircraft’s forward movement.
This led me to question the widely held assumption of 'low' forward speed at impact.

Based on the cL-AoA data posted earlier (ignoring ground effect), the following entirely hypothetical but mutually consistent numbers might be of interest for the purpose of recent scenario discussions:
Airspeed 300 kt CAS (M=0.453); vertical speed 40 fps (2400 fpm); loadfactor 2.5 g.
FPA (airdata) -4.5 deg., AoA 10.5 deg., pitch attitude 6 degrees.

HN39

Last edited by HazelNuts39; 9th May 2010 at 19:55. Reason: groundeffect
HazelNuts39 is offline  
Old 9th May 2010, 19:46
  #938 (permalink)  
 
Join Date: Sep 2009
Location: London, UK
Age: 57
Posts: 5
Satcom info

The satcom on aircraft is an electonically steerable phased array antenna with nominal gain 12dB (type CMA2102). The info in BEA report re a satcom drop out is, I am reliably informed, a misunderstanding by BEA and there is no conclusive evidence of a dropout.
Gualala is offline  
Old 9th May 2010, 19:59
  #939 (permalink)  
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 77
Posts: 1,330
snowfalcon2;
What if the first search planes on scene would as a standard practice drop, say, twenty tracer buoys (with GPS and a location transmitter) over the search area in order to map out the surface currents as accurately as possible? Then when debris is subsequently found, this "current map" would enable much more accurate pinpointing of the actual impact point.
Undoubtedly there will be lessons learned from this incident. Your suggestion is not new to this forum, and will obviously be borne in mind for the future - one hopes.

Bear in mind that the accident happened in a rather unpredictable part of the Equatorial North Atlantic, and even though there is satellite surface current and wind data available, the reliability of the data has not been sufficiently tested. My experience suggests that the surface current vectors - comprising both direction and speed were erroneous, and reference to other drifter data is not much help either. At low latitudes a coriolis correction may not have been needed in the smoothed data supplied. In fact, subtracting around 20 degrees from the vector angle and in creasing the velocity by 50 percent will have improved my original backtrack position enormously. I had, when arriving at that position, increased the velocity by a factor of 50 percent, and it was just the vector angle(s) that let me down.

Hindsight is a wonderful thing!

machinbird;
One way to achieve a tight ground referenced turn radius is to accomplish the majority of the turn in the vertical. This may be indicative of a LOC incident early on.
From Andy Tracy's A340/A330 Control: Flight Laws

Alternate 2 Pitch control laws are identical to Alternate 1. Lateral control law in roll is a direct law with a direct stick to surface position relationship. The gains are automatically set according to slats/flaps CONF. Yaw control law provides a Dutch roll damping function and damper authority is limited to +/4 rudder at CONF 0 and +/-15 in all other CONF. Turn coordination is provided with flat/slat extended. Protections are as in Alternate 1 except that there is no bank angle protection in ALT 2 and in the case of failure of 2 ADRs, no VSW prot and in the case of failure of 3 ADRs, no high speed protection. V/Mmo is reduced to 330/.82.

No turn coordination, RTLU locked, other distractions and the outcome could have been anything!

mm43
mm43 is offline  
Old 9th May 2010, 20:22
  #940 (permalink)  
 
Join Date: Jun 2009
Location: NNW of Antipodes
Age: 77
Posts: 1,330
Gualala;

I note from the CMA-2102 specs that the beam switch speed is less than 50uSec and the nominal 12dBi gain should be good provided the aircraft does not get in the way. I wonder why the BEA decided that there was LOS in the times they mentioned. Perhaps one day they will correct that error.

mm43
mm43 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.