BREAKING NEWS: airliner missing within Egyptian FIR
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CVR Forensics
Some recent posts have expressed skepticism about the interpretation of the final "noise" recorded by the CVR.
As an avid student of accident investigation, I have seen some instances over the years (no citations at the moment, I don't recall the specific accidents) in which fairly detailed inferences were made from CVR data.
Most obviously, the pressure level of a noise or shock can be estimated from the CVR recording. This in itself may be very useful in distinguishing a chemical explosion from an impact, metal fracture, or explosive decompression. Given the circumstances of the doomed flight, it's possible that the CVR recording captured several of these in NEAR synchrony -- tiny differences in timing will themselves serve as forensic clues.
Further, modern airliners are fitted with multiple Cockpit Area Microphones (CAMs). Comparing recordings from the various microphones can help to localize the direction from which the sound came, and to distinguish a loud sound from a shock wave*.
Conclusion: the investigators may have learned much more from the CVR, than the presence of a Loud Bang.
______________________________
* I've no idea how far the shock wave from a reasonable-size IED can travel in an A321 fuselage, so I can't say whether it's possible that an explosion far aft would produce a shock wave at the cockpit.
As an avid student of accident investigation, I have seen some instances over the years (no citations at the moment, I don't recall the specific accidents) in which fairly detailed inferences were made from CVR data.
Most obviously, the pressure level of a noise or shock can be estimated from the CVR recording. This in itself may be very useful in distinguishing a chemical explosion from an impact, metal fracture, or explosive decompression. Given the circumstances of the doomed flight, it's possible that the CVR recording captured several of these in NEAR synchrony -- tiny differences in timing will themselves serve as forensic clues.
Further, modern airliners are fitted with multiple Cockpit Area Microphones (CAMs). Comparing recordings from the various microphones can help to localize the direction from which the sound came, and to distinguish a loud sound from a shock wave*.
Conclusion: the investigators may have learned much more from the CVR, than the presence of a Loud Bang.
______________________________
* I've no idea how far the shock wave from a reasonable-size IED can travel in an A321 fuselage, so I can't say whether it's possible that an explosion far aft would produce a shock wave at the cockpit.
@lowca
What I meant was that for a small price, extra, unattended, heavy, or extra luggage can be loaded in the hold by the handlers. it is probably done everyday.
As you can see from another poster in France, the rule doesn't even exist there.
The flight crew would have have zero knowledge of any extra or unattended bags.
Having spent a lot of time in that part of the world flying commercially, unfortunately, I have seen things like this occur.
As you can see from another poster in France, the rule doesn't even exist there.
The flight crew would have have zero knowledge of any extra or unattended bags.
Having spent a lot of time in that part of the world flying commercially, unfortunately, I have seen things like this occur.
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Re explosion v decompression
Alain67 1527 post said IMO a spectral analyis would show the difference.
Right on- consider a major difference
An explosion makes as major increase in a positive pressure ( simplified as blowing into a ballon to inflate it )- and then followed by a decrease in pressure. As pressure decreases, sound intensity decreases- probably with little echo- Sound **speed** is a function of temperature not pressure. rapid decompression lowers temperature.
A decompression makes a major decrease in pressure.
Now both can sound the same to the ear- but any spectral analysis from several mikes should be able to immediately determine which happens first
Right on- consider a major difference
An explosion makes as major increase in a positive pressure ( simplified as blowing into a ballon to inflate it )- and then followed by a decrease in pressure. As pressure decreases, sound intensity decreases- probably with little echo- Sound **speed** is a function of temperature not pressure. rapid decompression lowers temperature.
A decompression makes a major decrease in pressure.
Now both can sound the same to the ear- but any spectral analysis from several mikes should be able to immediately determine which happens first
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@hamster3null: timing the explosion may not be that hard.
A mobile phone, or some other computing device with wireless communication, could easily talk to another device on the ground and update/modify an agreed upon deadline until contact is lost between the device on the ground and the on-board device. The last agreed upon time would be available to the second for whoever planted the device and their friends.
Letting the devices update the deadline automatically has the advantage of not involving the planter (no suspicious activity close to the plane) and you can do it frequently right up to the point of losing connection.
As for losing connection, this would depend on whether you use cellphone connections or wireless. Wireless might be cut when the doors are closed or, for instance, a catering truck with the ground device leaves the plane. Whether this is good enough depends on how smooth things normally go at the airport (never been there, so I wouldn't know).
I guess cellphone coverage for a planted device might last until you get up to a certain altitude at least? That would let the perps update the deadline based on exact takeoff time. SMS messages would give you plenty of bandwidth for final agreements (deadline update + ack), so you don't really need wireless.
If you assume that the mobile phone can connect to on-board wifi or cellphone networks, you will have more options for factors that can update the deadline (and still keep "ground" updated):
a) pressure as measured by the phone (my old Samsung phone does this, for instance)
b) location available through on-board wifi webpages (for instance). You probably don't need working GPS as the plane might give it to you freely
c) "ground crew" can update the deadline
Programming the devices isn't that hard. You don't have be a very advanced programmer to combine multiple techniques to get whatever works best that day.
1) If you only need it to go off some time after reaching a given altitude/pressure, it's almost trivial (depending on how safe you want to be that it doesn't go off early, but you might add other safeguards than programming).
2) If you need it to go off at a known point in time that's updated to the point of losing connection, it's really not that much harder and you can just set the deadline to a point where you're fairly certain it's well up in the air.
3) If you want to let it go off when passing a certain point (to some degree of accuracy), it's not really that much harder than (2). It's just down to how accurate you need to be, assumptions on flight paths and how long you can keep updating the timer. On-board communication at altitude can add accuracy, but would be more vulnerable and might be slightly more complicated to get working reliably.
Not that I want to argue that the video is real. I just don't think timing is an argument for debunking it.
A mobile phone, or some other computing device with wireless communication, could easily talk to another device on the ground and update/modify an agreed upon deadline until contact is lost between the device on the ground and the on-board device. The last agreed upon time would be available to the second for whoever planted the device and their friends.
Letting the devices update the deadline automatically has the advantage of not involving the planter (no suspicious activity close to the plane) and you can do it frequently right up to the point of losing connection.
As for losing connection, this would depend on whether you use cellphone connections or wireless. Wireless might be cut when the doors are closed or, for instance, a catering truck with the ground device leaves the plane. Whether this is good enough depends on how smooth things normally go at the airport (never been there, so I wouldn't know).
I guess cellphone coverage for a planted device might last until you get up to a certain altitude at least? That would let the perps update the deadline based on exact takeoff time. SMS messages would give you plenty of bandwidth for final agreements (deadline update + ack), so you don't really need wireless.
If you assume that the mobile phone can connect to on-board wifi or cellphone networks, you will have more options for factors that can update the deadline (and still keep "ground" updated):
a) pressure as measured by the phone (my old Samsung phone does this, for instance)
b) location available through on-board wifi webpages (for instance). You probably don't need working GPS as the plane might give it to you freely
c) "ground crew" can update the deadline
Programming the devices isn't that hard. You don't have be a very advanced programmer to combine multiple techniques to get whatever works best that day.
1) If you only need it to go off some time after reaching a given altitude/pressure, it's almost trivial (depending on how safe you want to be that it doesn't go off early, but you might add other safeguards than programming).
2) If you need it to go off at a known point in time that's updated to the point of losing connection, it's really not that much harder and you can just set the deadline to a point where you're fairly certain it's well up in the air.
3) If you want to let it go off when passing a certain point (to some degree of accuracy), it's not really that much harder than (2). It's just down to how accurate you need to be, assumptions on flight paths and how long you can keep updating the timer. On-board communication at altitude can add accuracy, but would be more vulnerable and might be slightly more complicated to get working reliably.
Not that I want to argue that the video is real. I just don't think timing is an argument for debunking it.
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Translation of parts of the French article
Crash dans le Sinaï : l'attentat confirmé par les boîtes noires - Le Point
Crash dans le Sinaï : l'attentat confirmé par les boîtes noires - Le Point
Quote:
Selon la source citée par l'Agence France-Presse, les photos des débris montrent que certains sont criblés d'impacts allant de l'intérieur vers l'extérieur de l'appareil, « ce qui accrédite plutôt la thèse d'un engin pyrotechnique ».
Crash dans le Sinaï : l'attentat confirmé par les boîtes noires - Le Point
Quote:
Selon la source citée par l'Agence France-Presse, les photos des débris montrent que certains sont criblés d'impacts allant de l'intérieur vers l'extérieur de l'appareil, « ce qui accrédite plutôt la thèse d'un engin pyrotechnique ».
criblés - 'riddled' - not evidenced in the photos here thus far, but genuinely crucial pieces may have already been removed, or not for public consumption.
Also, some debris 'may' be riddled on the inside, but have landed with the exterior up, so the damage isn't immediately visible without turning over.
I find the use of 'l'intérieur' interesting - when I first read that, I assumed it was meant to be passenger cabin, rather than somewhere like the the baggage hold. 'Inside' is a lot more vague.
From earlier in the article:
Le Cockpit Voice Recorder (CVR), l'une des boîtes noires, ne demande pas d'interprétation compliquée lors de la lecture, si ce n'est la traduction de propos en langue étrangère. Ce n'est qu'un magnétophone qui enregistre les conversations et les bruits du cockpit. Il révèle qu'une explosion est survenue. Ses effets dévastateurs ont coupé l'alimentation électrique de l'avion permettant, entre autres, les enregistrements des données dans les boîtes noires.
'no complex interpretation'??? - I think anyone with knowledge of previous incidents would beg to differ!
Caractère « brutal, soudain »
Le deuxième enregistreur, le Flight Data Recorder (FDR), capte des milliers de paramètres sur le vol concernant la vitesse, l'altitude, le régime des moteurs, le mode de pilotage, la position des gouvernes, etc. Pour cela, l'avion est truffé de capteurs. Une analyse fine au 1/100e de seconde des arrêts de ces capteurs permettrait de préciser la position dans l'avion de l'engin explosif. Selon une source proche du dossier citée par l'Agence France-Presse, le FDR confirme le caractère « brutal, soudain » de l'événement qui a précipité la chute de l'appareil. « Tout est normal, absolument normal pendant le vol, et brutalement plus rien. Cela va dans le sens de la soudaineté, du caractère immédiat de l'événement. »
Le deuxième enregistreur, le Flight Data Recorder (FDR), capte des milliers de paramètres sur le vol concernant la vitesse, l'altitude, le régime des moteurs, le mode de pilotage, la position des gouvernes, etc. Pour cela, l'avion est truffé de capteurs. Une analyse fine au 1/100e de seconde des arrêts de ces capteurs permettrait de préciser la position dans l'avion de l'engin explosif. Selon une source proche du dossier citée par l'Agence France-Presse, le FDR confirme le caractère « brutal, soudain » de l'événement qui a précipité la chute de l'appareil. « Tout est normal, absolument normal pendant le vol, et brutalement plus rien. Cela va dans le sens de la soudaineté, du caractère immédiat de l'événement. »
A "brutal, sudden" nature
The second recorder, the Flight Data Recorder (FDR), captures thousands of parameters on the flight regarding speed, altitude, engine speed, steering mode, the position of control surfaces, etc. For this, the aircraft is loaded with sensors. A detailed analysis of 1/100th of a second of the [last] of these [readings] would clarify the position on the plane of the explosive device. According to a source close to the case quoted by Agence France-Presse, the FDR confirms the "brutal, sudden" nature of the event that precipitated the fall of the [aircraft]. "Everything is normal, absolutely normal during the flight, and suddenly nothing. This [is] in line with the suddenness, the immediacy of the event."
Interesting that they think the sensors will reveal the device location. Would prefer to see the original AFP info - this article has certainly lent their own interpretation already to the few facts.
Brackets denote my interpretation of the original French.
(thanks to Mr Snuggles for the original link.)
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CONSO
You are perfectly correct, so long as the CVR continues to record for a few seconds after the initial pressure wave from either an explosion or explosive decompression. If the explosion or decompression event severs the data lines to the CVR at the instant it happens, only an initial high spike will be recorded and the remainder of the data is lost. So the vital reverberation information that would distinguish between an explosion or explosive decompression is not available for analysis.
It may be possible to estimate the strength of the initial leading edge of the pressure wave from the rise time before the signal to the CVR was lost. Slight time delays between the different microphone pickups can be used to localise the source. The further away the noise originated, the less accurate this will be. So an event at the rear of the aircraft can be positively identified as originating from that area, but whether it was behind the wing, in a rear baggage hold, or in the tail section will be very difficult to establish with any degree of accuracy.
You are perfectly correct, so long as the CVR continues to record for a few seconds after the initial pressure wave from either an explosion or explosive decompression. If the explosion or decompression event severs the data lines to the CVR at the instant it happens, only an initial high spike will be recorded and the remainder of the data is lost. So the vital reverberation information that would distinguish between an explosion or explosive decompression is not available for analysis.
It may be possible to estimate the strength of the initial leading edge of the pressure wave from the rise time before the signal to the CVR was lost. Slight time delays between the different microphone pickups can be used to localise the source. The further away the noise originated, the less accurate this will be. So an event at the rear of the aircraft can be positively identified as originating from that area, but whether it was behind the wing, in a rear baggage hold, or in the tail section will be very difficult to establish with any degree of accuracy.
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translation notes
papershuffler has the gist of it
"riddled by impacts passing from the interior of the plane to the exterior"
"The CVR, one of the black boxes, does not call for any complex interpretation other than the translation of comments in foreign languages. It is just a tape recorder that records conversations and sounds in the cockpit. It reveals that an explosion occurred. Its devastating effects cut off the electrical power of the aircraft which allows, inter alia, the recording of data in the black boxes".
[I'm a translator with minimal relevant technical knowledge beyond what I pick up reading here, but even I can tell bad journalese when I see it]
NB that the French "brutal" is weaker than the English homonym - means little more than "abrupt" here
"Analysis down to the nearest 1/100th of a second of the times these sensors failed would make it possible to identify the precise location of the explosive device in the aircraft."
[is that plausible? Presumably less likely if the event severed the connection to the FDR itself?]
criblés d'impacts allant de l'intérieur vers l'extérieur de l'appareil
Le Cockpit Voice Recorder (CVR), l'une des boîtes noires, ne demande pas d'interprétation compliquée lors de la lecture, si ce n'est la traduction de propos en langue étrangère.
[I'm a translator with minimal relevant technical knowledge beyond what I pick up reading here, but even I can tell bad journalese when I see it]
NB that the French "brutal" is weaker than the English homonym - means little more than "abrupt" here
Une analyse fine au 1/100e de seconde des arrêts de ces capteurs permettrait de préciser la position dans l'avion de l'engin explosif.
[is that plausible? Presumably less likely if the event severed the connection to the FDR itself?]
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Papershuffler
'no complex interpretation'??? - I think anyone with knowledge of previous incidents would beg to differ!
'no complex interpretation'??? - I think anyone with knowledge of previous incidents would beg to differ!
Regarding FDR and sensors depending where the explosion was and whether it or the end result in the rear severed the cabling there maybe some useful sensor info if they are lucky.
Basically they need duplicate cvr/fdr in the front or go to what what being propose during MH17 and have continuous data streaming of both, to an independent storage source which over writes BOTH at the same frequency as FDR (to avoid losing what may be useful cvr on long flights)
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re cvr data
You are perfectly correct, so long as the CVR continues to record for a few seconds after the initial pressure wave from either an explosion or explosive decompression.
As to the initial pressure wave- positive or negative- unless the explosion happened to immediately sever both power and multiple mike data lines at the same time, some trace should be available.
Ditto for a structural failure unzipping of aft section- which **might** give a few milliseconds more of data before both data and power lines are pulled apart.
yet the press and supposedly officials are saying definitely an explosive device ???
So why are there NO pics of jackscrew and horiz stab ' wingbox ' ??
CVR
For interest
There are pressure waves and structural borne waves, both longitudnal and lateral along the planes axis. The structure borne waves arrive the quickest and the decoding of these relative to any pressure waves is key to the location of the hammer blow etc.
Unfortunately or fortunately there is a data bank of previous CVRs to compare against, both for bombs and structural only failures.
I'm in the wait and see mode for what cards will be released in the news on this.
There are pressure waves and structural borne waves, both longitudnal and lateral along the planes axis. The structure borne waves arrive the quickest and the decoding of these relative to any pressure waves is key to the location of the hammer blow etc.
Unfortunately or fortunately there is a data bank of previous CVRs to compare against, both for bombs and structural only failures.
I'm in the wait and see mode for what cards will be released in the news on this.
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@Sultan,
I respectfully suggest that the account you offered of flight recorder performance in the helicopter accident reflects an imperfect recollection or interpretation of the events. I have two reasons for this:
1) Usually when buying a car, we don't ask, "does it have a motor, or is at least designed to be fitted with one?" ... because everyone understands that cars need motors! When specifying or designing a flight recorder, it ain't necessary to spell out "this thing should record data right up to final impact," because everyone knows that's the FUNDAMENTAL PURPOSE of a flight recorder. N'est ce pas?
2) I have reviewed Aviation Investigation Report A09A0016 issued by Canada's Transportation Safety Board, concerning the fatal ditching on 12 March 2009 of a Cougar Helicopters' Sikorsky S-92A.
This report says, "The MPFR* stopped recording about 44 seconds before impact and then began recording again about 1.7 seconds before the impact." The report attributes the data loss to an interruption of power to the recorder. Further, it finds that the likely cause of power interruption was activation of a g-switch intended to stop flight recorders when a crash occurs (?!?!).
If this is indeed the accident to which you refer, and the report is correct, then about 42 seconds of data were lost. Much more importantly, the quoted statement implies (strongly, to my mind) that the recorder captured and stored data up to the time of power interruption, and that recording promptly resumed when power was restored.
The report makes no reference to recorder buffering, latency or delay as a cause of the flight data loss. The report's sole finding with respect to the flight recorder, is that the use of g-switches to stop flight recorders is likely to result in data loss in future aviation incidents.
____________________________________________
If I've gotten any facts wrong, or misinterpreted anything, I welcome correction.
*Multi-Purpose Flight Recorder, a combination CVR/FDR
I respectfully suggest that the account you offered of flight recorder performance in the helicopter accident reflects an imperfect recollection or interpretation of the events. I have two reasons for this:
1) Usually when buying a car, we don't ask, "does it have a motor, or is at least designed to be fitted with one?" ... because everyone understands that cars need motors! When specifying or designing a flight recorder, it ain't necessary to spell out "this thing should record data right up to final impact," because everyone knows that's the FUNDAMENTAL PURPOSE of a flight recorder. N'est ce pas?
2) I have reviewed Aviation Investigation Report A09A0016 issued by Canada's Transportation Safety Board, concerning the fatal ditching on 12 March 2009 of a Cougar Helicopters' Sikorsky S-92A.
This report says, "The MPFR* stopped recording about 44 seconds before impact and then began recording again about 1.7 seconds before the impact." The report attributes the data loss to an interruption of power to the recorder. Further, it finds that the likely cause of power interruption was activation of a g-switch intended to stop flight recorders when a crash occurs (?!?!).
If this is indeed the accident to which you refer, and the report is correct, then about 42 seconds of data were lost. Much more importantly, the quoted statement implies (strongly, to my mind) that the recorder captured and stored data up to the time of power interruption, and that recording promptly resumed when power was restored.
The report makes no reference to recorder buffering, latency or delay as a cause of the flight data loss. The report's sole finding with respect to the flight recorder, is that the use of g-switches to stop flight recorders is likely to result in data loss in future aviation incidents.
____________________________________________
If I've gotten any facts wrong, or misinterpreted anything, I welcome correction.
*Multi-Purpose Flight Recorder, a combination CVR/FDR
Last edited by Etud_lAvia; 7th Nov 2015 at 04:21. Reason: Correct my atrocious French
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Speed of sound through the aircraft.
Wouldn't an high explosive event in the tail likely sever the electrical connections to the CVR before the sound could travel through the air to the microphones in the cockpit?
The speed of sound in Aluminum is about 15 times faster than the speed of sound in air. An explosive event would be rich in high frequency components and would travel through the structure and in effect, shake the structure holding the microphones and generate a signal in that manner. There would be a number of potential methods of analyzing the signals from the various cockpit microphones to confirm an explosive event.
If the event acoustic signal in the cockpit is an air carried signal, then the likelihood of a structural failure cause for the sound would be very high.
The speed of sound in Aluminum is about 15 times faster than the speed of sound in air. An explosive event would be rich in high frequency components and would travel through the structure and in effect, shake the structure holding the microphones and generate a signal in that manner. There would be a number of potential methods of analyzing the signals from the various cockpit microphones to confirm an explosive event.
If the event acoustic signal in the cockpit is an air carried signal, then the likelihood of a structural failure cause for the sound would be very high.
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It would travel through whatever medium at only a fraction of the speed of light, and then get back to the recorders in the tail at a theoretical limit of light speed. In actuality the return trip would be much slower. Summing up the two, the cables could have been severed before the round trip was over.
But, as has already been mentioned here, the actual severing of the cables may have sent a final signal to the recorders.
But, as has already been mentioned here, the actual severing of the cables may have sent a final signal to the recorders.
I've been intentionally staying out of this one, but something to consider:
I have little knowledge of the A320 series (given I work for brand B), but it is normal to provide significant separation between wire bundles to minimize the risk of a single failure taking out multiple systems. So it is reasonable to assume the wire routing to the CVR and DFDR were separated by several feet.
Pure speculation here, but it's quite possible that (assuming a bomb blast), the initial blast severed the wiring to the DFDR - hence no useable data. But some of the wiring to the CVR survived the initial blast. The bomb blast compromised the the fuselage and small debris exited the airframe (such as the unfortunate infant) while the pilots attempted to maintain control of a critically damaged aircraft while donning their oxygen masks (far too busy to contact ATC). Despite their best efforts, within a minute or so the aircraft completely broke up.
Again, purely speculation on my part, but it does fit the known data rather well.
I have little knowledge of the A320 series (given I work for brand B), but it is normal to provide significant separation between wire bundles to minimize the risk of a single failure taking out multiple systems. So it is reasonable to assume the wire routing to the CVR and DFDR were separated by several feet.
Pure speculation here, but it's quite possible that (assuming a bomb blast), the initial blast severed the wiring to the DFDR - hence no useable data. But some of the wiring to the CVR survived the initial blast. The bomb blast compromised the the fuselage and small debris exited the airframe (such as the unfortunate infant) while the pilots attempted to maintain control of a critically damaged aircraft while donning their oxygen masks (far too busy to contact ATC). Despite their best efforts, within a minute or so the aircraft completely broke up.
Again, purely speculation on my part, but it does fit the known data rather well.
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Regarding the rumour of 2 minute buffering of DFDRs - something
got lost in translation here and cannot be true. Furthermore, the
following specifications are listed for FDRs in EUROCAE ED-112
document, entitled "Minimum performance specifications" (PDF p.167):
Altitude/Speed/Heading: 1 Hz
Acceleration: 8 or 4 Hz
Control surfaces: 16 Hz
Pitch: 4 Hz
Roll: 2 Hz
Yaw: can't find it!
A copy of the full document is located here:
http://tinyurl.com/pen8ol6
@Etud - speaking of translations, here's a quick one:
It's not "Ne c'est pas?" but "N'est ce pas?"
Now back to regular programming...
got lost in translation here and cannot be true. Furthermore, the
following specifications are listed for FDRs in EUROCAE ED-112
document, entitled "Minimum performance specifications" (PDF p.167):
Altitude/Speed/Heading: 1 Hz
Acceleration: 8 or 4 Hz
Control surfaces: 16 Hz
Pitch: 4 Hz
Roll: 2 Hz
Yaw: can't find it!
A copy of the full document is located here:
http://tinyurl.com/pen8ol6
@Etud - speaking of translations, here's a quick one:
It's not "Ne c'est pas?" but "N'est ce pas?"
Now back to regular programming...
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thcrozier, you meant speed of sound, of course 
Both denoted by c
______________________________________
So, how might the CVR record the sound of a tail explosion via microphones in the nose?
To begin, I suggest that the investigators will probably be able to distinguish a microphone signal from a signal resulting from mechanical disturbance of the recorder and its wiring. (In electronic engineering, the generic term for this second category of signal is "microphonics".) To begin, the microphones probably have a well-characterized response to sound impulses which is quite slow in electronic terms. A microphonic signal resulting from a violent impact is likely to have a much steeper rise time.
Ordinary sound would take about 0.1 seconds to travel the length of the A321 pressure vessel.
From a high explosive, the pressure front would travel some part of the distance as a shock wave (supersonically) ... potentially at more than 10 times the speed of sound. Depending on how far the shock wave can propagate, the travel time might be substantially reduced.
To the extent that sound is conducted through the structure of the fuselage, it could reach the cockpit in 0.01 seconds, or even less.
So, if the CVR can survive as long as a tenth of second, or even less than that, it could be able to capture the sound of an explosion taking place quite near to it.
______________________________________
How long, then, might the CVR survive?
A high explosive shock wave can travel so quickly (possibly 20 times the speed of sound), that for the purposes of this disaster it is reasonable to estimate the travel time (from the point of explosion to the solid objects between that point and the CVR) as zero.
But in the path between a galley-area explosion and the CVR, there are several layers of material, including the structure of the galley itself, linings, insulation, and the pressure bulkhead.
The shock wave can get around these objects to the extent that gas-leakage paths exist, or are opened by the shock wave itself. However, the wave reaching the CVR probably didn't stop its functioning. It is a very hardened unit, and the intensity of the pressure wave was necessarily dissipated to some degree by the time it reached the CVR.
Most likely, what stopped the CVR was direct mechanical impact by parts of the airplane on the CVR itself, or its cabling.
Considering one possible sequence:
Although all these hypothetical events happen very fast, none of them are instantaneous. They all take time, and to some extent they are sequential (that is, one event does not begin until a preceding event has progressed to some extent).
I think it is plausible, and even probable, that whichever object hammered the CVR or its cabling could have taken a tenth of second to get there.
The blast wave can travel 20000 feet per second, but the solid object that killed the CVR may have been travelling more like 100 feet per second. Whatever speed it was going, it had to be accelerated to that velocity: it didn't reach it instantaneously.
Both denoted by c______________________________________
So, how might the CVR record the sound of a tail explosion via microphones in the nose?
To begin, I suggest that the investigators will probably be able to distinguish a microphone signal from a signal resulting from mechanical disturbance of the recorder and its wiring. (In electronic engineering, the generic term for this second category of signal is "microphonics".) To begin, the microphones probably have a well-characterized response to sound impulses which is quite slow in electronic terms. A microphonic signal resulting from a violent impact is likely to have a much steeper rise time.
Ordinary sound would take about 0.1 seconds to travel the length of the A321 pressure vessel.
From a high explosive, the pressure front would travel some part of the distance as a shock wave (supersonically) ... potentially at more than 10 times the speed of sound. Depending on how far the shock wave can propagate, the travel time might be substantially reduced.
To the extent that sound is conducted through the structure of the fuselage, it could reach the cockpit in 0.01 seconds, or even less.
So, if the CVR can survive as long as a tenth of second, or even less than that, it could be able to capture the sound of an explosion taking place quite near to it.
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How long, then, might the CVR survive?
A high explosive shock wave can travel so quickly (possibly 20 times the speed of sound), that for the purposes of this disaster it is reasonable to estimate the travel time (from the point of explosion to the solid objects between that point and the CVR) as zero.
But in the path between a galley-area explosion and the CVR, there are several layers of material, including the structure of the galley itself, linings, insulation, and the pressure bulkhead.
The shock wave can get around these objects to the extent that gas-leakage paths exist, or are opened by the shock wave itself. However, the wave reaching the CVR probably didn't stop its functioning. It is a very hardened unit, and the intensity of the pressure wave was necessarily dissipated to some degree by the time it reached the CVR.
Most likely, what stopped the CVR was direct mechanical impact by parts of the airplane on the CVR itself, or its cabling.
Considering one possible sequence:
- the blast wave (by a perhaps circuitous path) reaches the pressure bulkhead
- concurrently, overpressure both deforms & breaks the galley structure, and propels the pieces rearward like a piston
- in response to overpressure, and perhaps also the impact of objects that have become projectiles, the bulkhead deforms, first elastically and then plastically
- deformation of the pressure bulkhead exceeds its structural capacity, opening a rupture
- from this point, continued failure of the bulkhead is progressive ... the blast overpressure may already be dissipating, but cabin pressure is exerting about half a ton per square foot on the now compromised bulkhead
- static pressure and the dynamic forces from egress of cabin air peel open the initial crack(s)
- bulkhead material, or other pieces from the aircraft that have become projectiles, strike the CVR and/or its wiring
Although all these hypothetical events happen very fast, none of them are instantaneous. They all take time, and to some extent they are sequential (that is, one event does not begin until a preceding event has progressed to some extent).
I think it is plausible, and even probable, that whichever object hammered the CVR or its cabling could have taken a tenth of second to get there.
The blast wave can travel 20000 feet per second, but the solid object that killed the CVR may have been travelling more like 100 feet per second. Whatever speed it was going, it had to be accelerated to that velocity: it didn't reach it instantaneously.
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Is this the modus operandi for such a group
The ISIS who released the video also announced that they would let the world know shortly how they did this. Post the video they have remianed silent. This seems contrary to what the purpose of such a bombing would serve in their convoluted minds. Having not heard a peep out of them seems to indicate they were but hot air with their claims. if this was their eureka moment to claim fame with their leadership i am sure we would have heard more about it. Not discounting a human aspect to this but it also could be the act of one de ranged individual who boarded the aircraft with nothing more than a personal agenda.
Last edited by Wannabe Flyer; 7th Nov 2015 at 04:27. Reason: Grammer
