AF 447 Search to resume
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I certainly share your obvious frustration over the fact that in 2009 / 2010 we are in a position where a major aircraft accident occurs and we may not be able to gather the information as to "what really happened".
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Mr Optimistic
I believe it was analysis of the Crew Rest Module and various catering modules and perhaps o/h lockers that the BEA referred to when determining the likely(est) speed & trajectory of sea surface impact.
Plenty will correct if I am wrong, but as alwasy, its all back there in this or the original thread, for the reading thereof
rgds
I believe it was analysis of the Crew Rest Module and various catering modules and perhaps o/h lockers that the BEA referred to when determining the likely(est) speed & trajectory of sea surface impact.
Plenty will correct if I am wrong, but as alwasy, its all back there in this or the original thread, for the reading thereof
rgds
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Mr Optimistic
.... remind me of which recovered articles allowed the 'line of flight' BEA conclusion (ie is it in any doubt with respect to the whole airframe ?
From these observations it can be deduced that:
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 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 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.
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.
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.
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.
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36 g
Originally Posted by Mr Optimistic
There was a fair amount of discussion centred around arm '36g'. Can't say I followed it or why a piece should be rated according to a maximum inertial load as opposed to x N/mm^2. (...) Can anyone tell me the rated strength of a fastened seat belt and how that relates to the strength of the seat fixing, ...
Design loads for seats and belts are specified in FAR sections 25.561, 25.562 and 25.785(f)(3) which can be found here: PART 25—AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES
regards,
HN39
Thanks to all
Yep, I knew it was discussed a while back but the thread is a bit too long ! Thanks HN, I'll go away and read it. Must say I had imagined that a maximum design load would be based on a calculation of maximum aerodynamic loading without reference to the weight of the piece. I'll go look ! (edit: just have done, this will take some time !)
From what I understood from the 36g discussion, there was no mention of bending of the arm, is that not surprising even if the first motion/forces were all in the longtitudinal plane ?
From what I understood from the 36g discussion, there was no mention of bending of the arm, is that not surprising even if the first motion/forces were all in the longtitudinal plane ?
Last edited by Mr Optimistic; 12th Sep 2010 at 12:01. Reason: addition
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Mr.Optimistic
Why should Arm 36g bend if there was no failure of the rudder hinge arms?
The rudder hinge arms showed some cracking but had not failed. The hinge arm cracking can be explained by the ?partial failure? of Arm 36g causing some bending in a direction that they were not designed to resist.
From what I understood from the 36g discussion, there was no mention of bending of the arm, is that not surprising even if the first motion/forces were all in the longtitudinal plane ?
The rudder hinge arms showed some cracking but had not failed. The hinge arm cracking can be explained by the ?partial failure? of Arm 36g causing some bending in a direction that they were not designed to resist.
JD
Maybe some people did. We will never know. But if a person restrained in a seat fitted a jacket and didn't inflate it, then their body would still have sunk with their seat.
I am not saying that everyone would have put a jacket on. But I am a bit surprised that none of 51 people recovered had a jacket on. Not if they had been secured in a seat. Assuming they were still conscious, at some point some of the people on board would likely have realised that this was more than just turbulence and that they were going to crash. In the middle of the night over the middle of the ocean. And none of them thought to put a jacket on?
So either they were not able to (unconscious, or G-loads that prevented them from reaching their jackets). Or maybe the 51 recovered were not in a seat at all.
There had been suggestions early on in the original discussion that the plane may have ditched (possibly following a turn away from the weather), but the lack of a Mayday, the damage suggesting a high vertical speed, and the absence of life jackets I think together rule this out.
This then leaves 2 general scenarios with respect to how quickly everything unfolded.
1. Pax were all belted in, either because of increasing turbulence, or because of an aircraft problem. For whatever reason the situation subsequently deteriorated and the aircraft crashed.
2. Sudden and catastrophic loss of control. Pax not all seated as they were only in light turbulence prior to this. These pax were not able to get to a seat (nor a life jacket on), and these were the bodies recovered. Those pax that were belted in sank with their seats.
Either way, bear in mind that there were almost certainly more pax that (for whatever reason) did not sink with the aircraft than there were bodies found. Spotting a body at sea is not easy at all. It is almost certain that some bodies were simply not found despite best efforts. So either a lot of people were not restrained, or if everyone was restrained than a lot of bodies worked themselves free of the seat before the seat sank.
228 people - 216 pax, 3 flight crew, 9 cabin crew. They found 51 bodies, and were able to ID 50 of these. Of these 50 - 1 pilot (Captain - possibly having rest period), 4 flight attendants, 45 pax. You probably wouldn't expect to recover either of the pilots on the flightdeck if they were restrained. So they found 4/9 cabin crew, 1 pilot (perhaps not on the flightdeck) and 45/216 pax. That's a bid odd - certainly not impossible, but a little surprising. I would have to go back to high school maths to work out the odds, but the cabin crew are certainly over-represented among the recovered. Perhaps the sort of ratio you would normally expect to find unrestrained mid-flight - cabin crew working, some pax up and about, some pax seated but unrestrained, and some pax restrained.
By itself, you could easily accept this as a statistical quirk. One or two fewer CC, and the ratio would be the same as the pax. But, the cabin crew harnesses are not a lap belt only. They fit over the shoulders and join the lap belt at a common buckle.
http://www.bea.aero/docspa/2009/f-cp...90601e2.en.pdf page 16
And I think it pretty unlikely that a body would work itself free from one of the crew seats. Certainly not 4/9.
Also, 3 crew seats were found - empty, belts not secured, and not that broken up (suggesting not supporting a person at impact).
And so IMO you really have to conclude that the cabin crew at least were not secured at impact.
So I think this all points to sudden and total loss of control not preceded by anything more than light turbulence. It doesn't really point to either structural failure of the aircraft, or some form of stall due to pitot problems / faulty airspeed readings. All it suggests (fairly compellingly I believe) is that whatever happened was sudden and very severe.
A couple of additional thoughts:
1. Despite all the advances in technology, we had a better idea where to find the Titanic than we do AF447 almost 100 years later. I know the much greater speed of aircraft makes the "circle" much larger, and I know that it flew (one way or another) from 35000 before it hit the water. But maybe we need better real time tracking of aircraft position - especially overwater, and in this age of heightened terrorism threat.
2. I know this has been mentioned previously, but the recorders have proven that they are not designed to be recovered from deep water. There are lots of possible solutions to this deficiency - everything from more powerful if less frequent pingers, to some system where they break free from the wreckage. AF447 alone surely dictates that this be addressed.
Please answer a simple question - how do the people get their life vests out when they are strapped into their seats in heavy turbulence? Even if they were in the seat back pouches why would they unless the plane was known to be about to ditch?
I am not saying that everyone would have put a jacket on. But I am a bit surprised that none of 51 people recovered had a jacket on. Not if they had been secured in a seat. Assuming they were still conscious, at some point some of the people on board would likely have realised that this was more than just turbulence and that they were going to crash. In the middle of the night over the middle of the ocean. And none of them thought to put a jacket on?
So either they were not able to (unconscious, or G-loads that prevented them from reaching their jackets). Or maybe the 51 recovered were not in a seat at all.
There had been suggestions early on in the original discussion that the plane may have ditched (possibly following a turn away from the weather), but the lack of a Mayday, the damage suggesting a high vertical speed, and the absence of life jackets I think together rule this out.
This then leaves 2 general scenarios with respect to how quickly everything unfolded.
1. Pax were all belted in, either because of increasing turbulence, or because of an aircraft problem. For whatever reason the situation subsequently deteriorated and the aircraft crashed.
2. Sudden and catastrophic loss of control. Pax not all seated as they were only in light turbulence prior to this. These pax were not able to get to a seat (nor a life jacket on), and these were the bodies recovered. Those pax that were belted in sank with their seats.
Either way, bear in mind that there were almost certainly more pax that (for whatever reason) did not sink with the aircraft than there were bodies found. Spotting a body at sea is not easy at all. It is almost certain that some bodies were simply not found despite best efforts. So either a lot of people were not restrained, or if everyone was restrained than a lot of bodies worked themselves free of the seat before the seat sank.
228 people - 216 pax, 3 flight crew, 9 cabin crew. They found 51 bodies, and were able to ID 50 of these. Of these 50 - 1 pilot (Captain - possibly having rest period), 4 flight attendants, 45 pax. You probably wouldn't expect to recover either of the pilots on the flightdeck if they were restrained. So they found 4/9 cabin crew, 1 pilot (perhaps not on the flightdeck) and 45/216 pax. That's a bid odd - certainly not impossible, but a little surprising. I would have to go back to high school maths to work out the odds, but the cabin crew are certainly over-represented among the recovered. Perhaps the sort of ratio you would normally expect to find unrestrained mid-flight - cabin crew working, some pax up and about, some pax seated but unrestrained, and some pax restrained.
By itself, you could easily accept this as a statistical quirk. One or two fewer CC, and the ratio would be the same as the pax. But, the cabin crew harnesses are not a lap belt only. They fit over the shoulders and join the lap belt at a common buckle.
http://www.bea.aero/docspa/2009/f-cp...90601e2.en.pdf page 16
And I think it pretty unlikely that a body would work itself free from one of the crew seats. Certainly not 4/9.
Also, 3 crew seats were found - empty, belts not secured, and not that broken up (suggesting not supporting a person at impact).
And so IMO you really have to conclude that the cabin crew at least were not secured at impact.
So I think this all points to sudden and total loss of control not preceded by anything more than light turbulence. It doesn't really point to either structural failure of the aircraft, or some form of stall due to pitot problems / faulty airspeed readings. All it suggests (fairly compellingly I believe) is that whatever happened was sudden and very severe.
A couple of additional thoughts:
1. Despite all the advances in technology, we had a better idea where to find the Titanic than we do AF447 almost 100 years later. I know the much greater speed of aircraft makes the "circle" much larger, and I know that it flew (one way or another) from 35000 before it hit the water. But maybe we need better real time tracking of aircraft position - especially overwater, and in this age of heightened terrorism threat.
2. I know this has been mentioned previously, but the recorders have proven that they are not designed to be recovered from deep water. There are lots of possible solutions to this deficiency - everything from more powerful if less frequent pingers, to some system where they break free from the wreckage. AF447 alone surely dictates that this be addressed.
Galley
From what I recall the recovered galley still had a number of drawers in place. Can anything be deduced from this regarding the dynamics of the motion (on the off chance that this might point away from hi loads before impact).
There was a post way back showing best guess seat positions for teh recovered individuals. Again from memory, I think these were widely distributed in the aircraft. Perhaps this also indicates that the discriminator was seated/not seated rather than position. However, since the pathology was only obtained from these, and that was consistent (apparently) with being seated, all seems mysterious.
There was a post way back showing best guess seat positions for teh recovered individuals. Again from memory, I think these were widely distributed in the aircraft. Perhaps this also indicates that the discriminator was seated/not seated rather than position. However, since the pathology was only obtained from these, and that was consistent (apparently) with being seated, all seems mysterious.
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Deja vu?
from another thread by Seagul1 on 14 May 2009.
Could this be applicable to AF447?
Airbus 330
Both Eng bleeds inop after take off in short succession couple off resets carried out with no success. ECAM did not sense the second Eng Bleed inop. No ECAM associated with losing pressurisation. No ECAM except the fault light on the overhead panel on second eng bleed. Used the APU bleed to land...
Both Eng bleeds inop after take off in short succession couple off resets carried out with no success. ECAM did not sense the second Eng Bleed inop. No ECAM associated with losing pressurisation. No ECAM except the fault light on the overhead panel on second eng bleed. Used the APU bleed to land...
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Seat Belts and Life Vests
This is an issue that concerned me many times as a passenger when preparing for a flight - whilst listening and watching the safety demonstration.
As a normal passenger I wouldn't even know what I am looking for under the seat - sorry - did I say looking?!? I only can feel and touch for "something" underneath the seat while sitting down strapped in! Sorry folks - but no one has ever shown me, or any other passenger on any flight I have been on, what I am "looking" for under the seat!?
Furthermore, the demonstration clearly shows how to put on the life vest and secure it - "strap around your waste - pull to tighten" - however - try to put the life vest on, if you even can find it under the seat (whilst sitting down and securly strapped in) whilst sitting in the seat and strapped in!?!? As far as I am concerned - no way.
Now my version of events on board of that fatal flight AF447:
From a passenger's perspective - the first thing that usually happens in the advent of turbulence ist the "Seatbelt Sign" turned on - usually followed by a cabin crew announcement of the same.
I would therefore suggest that, more or less, everyone on board was sitting down, securely strapped in INCLUDING all of the crew with their four-point safety harness (not just a seat belts).
I further suggest that the flight deck, at some point, realised their extreme problems and allerted the cabin "to prepare for ditching" - possibly even by the captain himself trying to calm the situation and therfore making his way into the passenger compartment- hence he is not sitting down strapped in at this point in time.
All passengers on board are now scrambling for life vests under their seats and to put them on as instructed. To do so they HAVE to undo their seat belts, get up, put on the life vests, sit down again and strap back in. There would have been some panic on board, some people may need help - so some of the cabin crew get up to assist - now they are no longer strapped in either. Some peassengers may not be able to sit down at all, due to the rapid downwards drop of the plane!
If at this point the impact does occure I would not be surprised that about 50 passengers are not strapped into their seatbelts including some of the crew which did attempt to help - nor am I not surpised that no life vests are found used - there would simply not have been enough time - a few minutes to move 228 passengers from their seats and back in?!?!
As an aside: Next flight I am on I will endeavour to lay on the floor and look for that "life vest" ...
As a normal passenger I wouldn't even know what I am looking for under the seat - sorry - did I say looking?!? I only can feel and touch for "something" underneath the seat while sitting down strapped in! Sorry folks - but no one has ever shown me, or any other passenger on any flight I have been on, what I am "looking" for under the seat!?
Furthermore, the demonstration clearly shows how to put on the life vest and secure it - "strap around your waste - pull to tighten" - however - try to put the life vest on, if you even can find it under the seat (whilst sitting down and securly strapped in) whilst sitting in the seat and strapped in!?!? As far as I am concerned - no way.
Now my version of events on board of that fatal flight AF447:
From a passenger's perspective - the first thing that usually happens in the advent of turbulence ist the "Seatbelt Sign" turned on - usually followed by a cabin crew announcement of the same.
I would therefore suggest that, more or less, everyone on board was sitting down, securely strapped in INCLUDING all of the crew with their four-point safety harness (not just a seat belts).
I further suggest that the flight deck, at some point, realised their extreme problems and allerted the cabin "to prepare for ditching" - possibly even by the captain himself trying to calm the situation and therfore making his way into the passenger compartment- hence he is not sitting down strapped in at this point in time.
All passengers on board are now scrambling for life vests under their seats and to put them on as instructed. To do so they HAVE to undo their seat belts, get up, put on the life vests, sit down again and strap back in. There would have been some panic on board, some people may need help - so some of the cabin crew get up to assist - now they are no longer strapped in either. Some peassengers may not be able to sit down at all, due to the rapid downwards drop of the plane!
If at this point the impact does occure I would not be surprised that about 50 passengers are not strapped into their seatbelts including some of the crew which did attempt to help - nor am I not surpised that no life vests are found used - there would simply not have been enough time - a few minutes to move 228 passengers from their seats and back in?!?!
As an aside: Next flight I am on I will endeavour to lay on the floor and look for that "life vest" ...
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life jackets
Read the NTSB report into the Hudson ditching with regard to life jackets.
They note the dificulty in extracting life jackets from their retainers and the understandable reaction of the passangers not to continue trying but to get out.
Now imagine doing this on your own initiative probably in the dark whilst in a turbulant descent. Further the instruction on use states: do not inflate until outside the aircraft.
With regard to bodies seperating from seats whilst strapped in there are plenty of crashes on land where this has ocured - why so unlikly on water?
Jumpers from tall buildings often bounce
Wtech the captain would not have left the cockpit under these circumstances and if he was in the rest area he would have been trying to get back to the cockpit if possible.
With regard to the high number of cabin crew - observe what they do after a service. Usually congregate in their galleys and chat. This group could have been in one area that allowed their bodies to escape the fusalage.
They note the dificulty in extracting life jackets from their retainers and the understandable reaction of the passangers not to continue trying but to get out.
Now imagine doing this on your own initiative probably in the dark whilst in a turbulant descent. Further the instruction on use states: do not inflate until outside the aircraft.
With regard to bodies seperating from seats whilst strapped in there are plenty of crashes on land where this has ocured - why so unlikly on water?
Jumpers from tall buildings often bounce
Wtech the captain would not have left the cockpit under these circumstances and if he was in the rest area he would have been trying to get back to the cockpit if possible.
With regard to the high number of cabin crew - observe what they do after a service. Usually congregate in their galleys and chat. This group could have been in one area that allowed their bodies to escape the fusalage.
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Seat Belts and Life Jackets
Certainly possible scenarios I believe...
What about 'nobody of the passengers/cabin crew was aware that there was trouble until shortly before the impact with the ocean'.
Do we know whether everything was ok in the cockpit? What happens if aircraft automatically changes to alternate law and pilots do not overtake command (because they are not able to do so for whatever reason)?
Can these things be ruled out with the information we have?
WB
What about 'nobody of the passengers/cabin crew was aware that there was trouble until shortly before the impact with the ocean'.
Do we know whether everything was ok in the cockpit? What happens if aircraft automatically changes to alternate law and pilots do not overtake command (because they are not able to do so for whatever reason)?
Can these things be ruled out with the information we have?
WB
Well here goes nothing. aa Been wondering for a long time if I should post here or not, but let's try it. As a warning - I have nil aviation background, I do deal with complex (computer) systems and their interactions.
Reading through the various documents available I'm still left very much puzzled as to the sequence of events. What is really puzzling is that from everything I've read I still feel AF447 was at least somewhat controllable (very low bank angle, relatively speaking normal pitch) until the very end, yet somehow they've ended up 30.000+ ft lower than at the start of the event sequence.
So a short analysis and a bit of speculation (please feel free to comment on the issues I have most probably gotten completely wrong).
0210Z - AF447 has been passing through an active cell, but has reached a zone of severe icing, and the pitot probes are starting to ice over (at varying speeds due to sightly different air flows). That far is clear. For this reason at 0211Z ADR2 is classified as faulty (fed by starboard side pitot probes), and the F/O presumably switched to ADR3 (the stby ADR), at 0212Z the remaining ADIRUs disagree and the NAV ADR DISAGREE message is sent via ACARS. AF447 is now without reliable air speed infication. Presumably we all agree thus far.
What they are left with is the GPS GS speed in the GPS monitor page. It is logical to presume that this (ADR2 failure) was the cause of the regression from normal law to alternate law (the 0210Z ATA: 279100 message), and the message at 0211Z explains the regression to ALTN law.
What is missing at this point is the regression to direct law - from everything I've read triple ADR failure causes a regression from alternate to direct law. I would have expected to see this message no later than 0213Z (but presumably even before NAV ADR DISAGREE).
Highly speculative part follows: Due to the fact that I cannot comprehend that an airplane with working engines and still fairly normally controllable (okay, with lost protections, but at least still somewhat controllable) flies into the ocean I speculate that the engines might not have been working at this time any longer.
Let me explain - I speculate that AF447 might have been caught in a massive updraft around 0214Z that pushed them considerably higher while at the same time causing compressor stalls in both engines (I presume the updraft would also cause massive airflow disruption into the engine).
At 0214Z the last ACARS message received was "CABIN VERTICAL SPEED". Can someone advise if this would necessarily mean a rapid descent or if it were possible that the static ports were also icing over (and due to simple physics when the "hole" is smaller the same amount of air moves faster through it and causes a reading of higher pressure (and as a consequence a lower altitude).
If the engines stopped working around 0214Z (from what I remember another ACARS message was supposed to be received no later than 0215Z), and I stress I might have gotten this totally incorrect, the RAT would have been deployed and the AC1, AC2, DC1 and DC2 busess would be left unpowered and only the DC ESS and AC ESS busses would be powered. Now if I read correctly then ACARS is powered by AC1, and once normal electrical power is lost, ACARS remains unpowered (which would explain the cessation of ACARS communications after 0214Z).
Also speculative is the assumption that they were unsuccessful in restarting the engines (reason uknown? potentially already in a deep stall at that point and simply running out of time) and might have attempted a ditching that did not succeed (but on a storm night with very low visibility and unreliable indications of at least speed, but probably also altitude and onto a water surface that was quite likely far from calm ... unfortunately they couldn't have done it). Again - this is highly speculative, I have nil aviation background, so be gentle in pointing out the mistakes in my thought process.
D.
Reading through the various documents available I'm still left very much puzzled as to the sequence of events. What is really puzzling is that from everything I've read I still feel AF447 was at least somewhat controllable (very low bank angle, relatively speaking normal pitch) until the very end, yet somehow they've ended up 30.000+ ft lower than at the start of the event sequence.
So a short analysis and a bit of speculation (please feel free to comment on the issues I have most probably gotten completely wrong).
0210Z - AF447 has been passing through an active cell, but has reached a zone of severe icing, and the pitot probes are starting to ice over (at varying speeds due to sightly different air flows). That far is clear. For this reason at 0211Z ADR2 is classified as faulty (fed by starboard side pitot probes), and the F/O presumably switched to ADR3 (the stby ADR), at 0212Z the remaining ADIRUs disagree and the NAV ADR DISAGREE message is sent via ACARS. AF447 is now without reliable air speed infication. Presumably we all agree thus far.
What they are left with is the GPS GS speed in the GPS monitor page. It is logical to presume that this (ADR2 failure) was the cause of the regression from normal law to alternate law (the 0210Z ATA: 279100 message), and the message at 0211Z explains the regression to ALTN law.
What is missing at this point is the regression to direct law - from everything I've read triple ADR failure causes a regression from alternate to direct law. I would have expected to see this message no later than 0213Z (but presumably even before NAV ADR DISAGREE).
Highly speculative part follows: Due to the fact that I cannot comprehend that an airplane with working engines and still fairly normally controllable (okay, with lost protections, but at least still somewhat controllable) flies into the ocean I speculate that the engines might not have been working at this time any longer.
Let me explain - I speculate that AF447 might have been caught in a massive updraft around 0214Z that pushed them considerably higher while at the same time causing compressor stalls in both engines (I presume the updraft would also cause massive airflow disruption into the engine).
At 0214Z the last ACARS message received was "CABIN VERTICAL SPEED". Can someone advise if this would necessarily mean a rapid descent or if it were possible that the static ports were also icing over (and due to simple physics when the "hole" is smaller the same amount of air moves faster through it and causes a reading of higher pressure (and as a consequence a lower altitude).
If the engines stopped working around 0214Z (from what I remember another ACARS message was supposed to be received no later than 0215Z), and I stress I might have gotten this totally incorrect, the RAT would have been deployed and the AC1, AC2, DC1 and DC2 busess would be left unpowered and only the DC ESS and AC ESS busses would be powered. Now if I read correctly then ACARS is powered by AC1, and once normal electrical power is lost, ACARS remains unpowered (which would explain the cessation of ACARS communications after 0214Z).
Also speculative is the assumption that they were unsuccessful in restarting the engines (reason uknown? potentially already in a deep stall at that point and simply running out of time) and might have attempted a ditching that did not succeed (but on a storm night with very low visibility and unreliable indications of at least speed, but probably also altitude and onto a water surface that was quite likely far from calm ... unfortunately they couldn't have done it). Again - this is highly speculative, I have nil aviation background, so be gentle in pointing out the mistakes in my thought process.
D.
Last edited by damirc; 18th Sep 2010 at 11:36. Reason: Legibility.
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At 0214Z the last ACARS message received was "CABIN VERTICAL SPEED". Can someone advise if this would necessarily mean a rapid descent or if it were possible that the static ports were also icing over (and due to simple physics when the "hole" is smaller the same amount of air moves faster through it and causes a reading of higher pressure (and as a consequence a lower altitude).
but can it be, that the startic port reach a zone of lower presure behind the hull during spin or stall??----> massage "cabin vertical speed"
grity
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.. slowly stooping to clutching at straws, maybe.
Static pressure sensing is not about movement of air through ports, its about transmission of pressure signals through them, involving minimal or zero flow
In fact pitot (dynamic head) reading also involves pressur sensing but no significant flow
At 0214Z the last ACARS message received was "CABIN VERTICAL SPEED". Can someone advise if this would necessarily mean a rapid descent or if it were possible that the static ports were also icing over (and due to simple physics when the "hole" is smaller the same amount of air moves faster through it and causes a reading of higher pressure (and as a consequence a lower altitude).
In fact pitot (dynamic head) reading also involves pressur sensing but no significant flow
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damirc , having read through mme zimmerman's report there is a a page showing af447 maintenance issues and curious enough from the start of may until the end of may the pilots of various flights reported 9 times of vibration on engine number 1 . Each time the response from service engineers was that ' it was within tolerances ' . Your comment about the pilots being unable to restart the engines may be closer to reality than others may think.
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static sensor
@HarryMann
i think, the only place with nearly no airflow around a hull is the middle of the nose, but there is a lot of dynamic high-pressure,
the place where the static sensor read the equivalent presure of the air around the plane, is a very smal area, between the high-presure in the front and the lower presure at the side of the hull
in case of a spinn, this area is more or less moving over the hull back (or forth) and the static sensore is IMO than not longer at the right place to read a correct static-air-presure.....
my question is, can this wrong "static" presure generate into the system the message: "cabin vertical speed" ? grity
i think, the only place with nearly no airflow around a hull is the middle of the nose, but there is a lot of dynamic high-pressure,
the place where the static sensor read the equivalent presure of the air around the plane, is a very smal area, between the high-presure in the front and the lower presure at the side of the hull
in case of a spinn, this area is more or less moving over the hull back (or forth) and the static sensore is IMO than not longer at the right place to read a correct static-air-presure.....
my question is, can this wrong "static" presure generate into the system the message: "cabin vertical speed" ? grity
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grity
The basic difference between a Static Source and a Pitot is ninety degrees. I just go from there.
I had a chance last week to clamber around an A300. Noticed first of all four Pitot tubes (two on each side, F/O & Alt.; Capt.&Alt). I'm pretty sure that AF447 (A330) has three?). These tubes were unusually (?) long, not sure the significance of that. Each probe appeared to be ~12 inches long.
bear
The basic difference between a Static Source and a Pitot is ninety degrees. I just go from there.
I had a chance last week to clamber around an A300. Noticed first of all four Pitot tubes (two on each side, F/O & Alt.; Capt.&Alt). I'm pretty sure that AF447 (A330) has three?). These tubes were unusually (?) long, not sure the significance of that. Each probe appeared to be ~12 inches long.
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Cabin V/S Advisory
Originally Posted by grity
my question is, can this wrong "static" presure generate into the system the message: "cabin vertical speed" ?
regards,
HN39
Well after a lot of reading I've finally found out a few more interesting things.
"CABIN VERTICAL SPEED" is triggered if the cabin air pressure changes with an excess rate of over 1800 fpm (either +/-) over 5 seconds - so a 150 ft cabin alt pressure change over 5 seconds will trigger this alert.
We can't be sure what the cabin alt pressure was set to, but due to the fact that this was a longer sector (documents state that under 2,5 hours it is typically set to 8000 ft, over 2,5 hours it's typically set to 7350 ft) it might have been 7350 ft.
One way to trigger that event is busting pressure difference limits (+8.85 psi, -0.26 psi iirc) due to a descent below an altitude where there pressure difference would have been in excess (in absolute terms) of -0.26 psi (I did some calculations and it would have been slightly below 5000 ft MSL) or severe air pressure drop in the environment. If the air pressure difference went above -0.26 psi they went from FL350 to 5000 ft in under 5 minutes, so their descent rate would have been in excess of 6000 fpm
. Another alternative would be a decompression, but the fact that none of the recovered passenger oxygen masks were deployed (found stowed) speaks rather against this.
Not completely sure how much pressure is lost with normal cruise outflow valve positions and the (completely normal) imperfect seals - but could it be possible that engines spooling down simply caused the rise of cabin alt pressure (so it went from 7350 ft to above 7500 ft within 5 seconds) - if that were true then that last message could also confirm the loss of engine power. Highly speculative (and very unlikely to say the least), but trying to think outside of the box.
I will also have to second guess my own statements that it could have been a ditching gone bad ... 0 flaps speaks against this (reread the BEA documents).
After rereading the BEA documents one specific passage caught my eye. The NAV TCAS fault logged via ACARS at 0210Z could have been cause either by an electric fault or the standard altitude being rejected by the TCAS system for not passing the credibility test (ie: what was read from ADR1 or ADR2) - while not knowing the exact procedure of the credibility test I would imagine that AoA and previous altitude would be used to predict the new value and allow for some tolerance. If they did get caught up in a massive updraft I could imagine the predicted value being too different from the read altitude. The other alternative is incorrect altitude readings received from the ADRs - which would quite likely mean that besides their speed indication being unreliable (apart from the GPS deduced values in the GPS monitor) also their altitude indication was unreliable. With that in mind - they were effectively blind and relying on the standby attitude indicator, the EPR/N1 indication to try to maintain altitude and speed, and the GPS speed + GPS alt values (which would be rather "laggy").
So after exploring all of this I only see 2 options of the reason for the disaster:
1) loss of control due to disorientation (hitting the water near wing level is somewhat odd for this speculation, but possible if they entered a sequence of stalls that they did manage to recover from - until the last one)
2) loss of engine power and subsequent ditching (0 flaps speaks very much against this, also all of the debris starting point location (path regression) also favor the first option)
D.
"CABIN VERTICAL SPEED" is triggered if the cabin air pressure changes with an excess rate of over 1800 fpm (either +/-) over 5 seconds - so a 150 ft cabin alt pressure change over 5 seconds will trigger this alert.
We can't be sure what the cabin alt pressure was set to, but due to the fact that this was a longer sector (documents state that under 2,5 hours it is typically set to 8000 ft, over 2,5 hours it's typically set to 7350 ft) it might have been 7350 ft.
One way to trigger that event is busting pressure difference limits (+8.85 psi, -0.26 psi iirc) due to a descent below an altitude where there pressure difference would have been in excess (in absolute terms) of -0.26 psi (I did some calculations and it would have been slightly below 5000 ft MSL) or severe air pressure drop in the environment. If the air pressure difference went above -0.26 psi they went from FL350 to 5000 ft in under 5 minutes, so their descent rate would have been in excess of 6000 fpm
. Another alternative would be a decompression, but the fact that none of the recovered passenger oxygen masks were deployed (found stowed) speaks rather against this.Not completely sure how much pressure is lost with normal cruise outflow valve positions and the (completely normal) imperfect seals - but could it be possible that engines spooling down simply caused the rise of cabin alt pressure (so it went from 7350 ft to above 7500 ft within 5 seconds) - if that were true then that last message could also confirm the loss of engine power. Highly speculative (and very unlikely to say the least), but trying to think outside of the box.
I will also have to second guess my own statements that it could have been a ditching gone bad ... 0 flaps speaks against this (reread the BEA documents).
After rereading the BEA documents one specific passage caught my eye. The NAV TCAS fault logged via ACARS at 0210Z could have been cause either by an electric fault or the standard altitude being rejected by the TCAS system for not passing the credibility test (ie: what was read from ADR1 or ADR2) - while not knowing the exact procedure of the credibility test I would imagine that AoA and previous altitude would be used to predict the new value and allow for some tolerance. If they did get caught up in a massive updraft I could imagine the predicted value being too different from the read altitude. The other alternative is incorrect altitude readings received from the ADRs - which would quite likely mean that besides their speed indication being unreliable (apart from the GPS deduced values in the GPS monitor) also their altitude indication was unreliable. With that in mind - they were effectively blind and relying on the standby attitude indicator, the EPR/N1 indication to try to maintain altitude and speed, and the GPS speed + GPS alt values (which would be rather "laggy").
So after exploring all of this I only see 2 options of the reason for the disaster:
1) loss of control due to disorientation (hitting the water near wing level is somewhat odd for this speculation, but possible if they entered a sequence of stalls that they did manage to recover from - until the last one)
2) loss of engine power and subsequent ditching (0 flaps speaks very much against this, also all of the debris starting point location (path regression) also favor the first option)
D.