FDR/CVR recovery problems/solutions
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FDR/CVR recovery problems/solutions
Hello,
maybe the real-time data transmission is the future, but as a simple solution for the existing FDR/CVR-system I have a question which most likely has already been asked:
Could there be a little release system (comparable to the airbag in a car) attached to the FDR/CVR-units that releases a buoyancy device at a defined pressure (= depth of water) so that there will never be a FDR/CVR at the sea-floor, but on the ocean sea-surface only for easy recovery ?
I am a meteorologist and on research ship expeditions (R/V Polarstern) it is a standard technology to deploy oceanographic moorings which register data for several months. They have buoyancy devices attached which are remotely separated from the mooring base (typically a railroad wheel) so that the complete mooring with all registration units will come up to the sea-surface to be recovered.
Is this too simple an idea ?
Regards, Bernd.
maybe the real-time data transmission is the future, but as a simple solution for the existing FDR/CVR-system I have a question which most likely has already been asked:
Could there be a little release system (comparable to the airbag in a car) attached to the FDR/CVR-units that releases a buoyancy device at a defined pressure (= depth of water) so that there will never be a FDR/CVR at the sea-floor, but on the ocean sea-surface only for easy recovery ?
I am a meteorologist and on research ship expeditions (R/V Polarstern) it is a standard technology to deploy oceanographic moorings which register data for several months. They have buoyancy devices attached which are remotely separated from the mooring base (typically a railroad wheel) so that the complete mooring with all registration units will come up to the sea-surface to be recovered.
Is this too simple an idea ?
Regards, Bernd.
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Hi Bernd
A CVR/DFDR is located in the rear unpressurized fuselage, mounted on a shelf. It would make no sense to let it afloat. And BTW how many crashes like this happend in the past.
A CVR/DFDR is located in the rear unpressurized fuselage, mounted on a shelf. It would make no sense to let it afloat. And BTW how many crashes like this happend in the past.
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Bernd,
Buoyancy devices make little sense because air crashes are so unpredicatable.
Think of somethng like the Hudson crash... imagine a larger impact, more waves, and the tail would have broken off, then sunk. Any buoyancy devices would have dragged the CVR and FDR into the tip of the tail and they would have been dragged down with it.
Most crashes involve high-g impacts and fire, which is what CVRs and FDRs are protected against in the first place. Some do occur over water, which is why there are are ULBs.
CJ
Buoyancy devices make little sense because air crashes are so unpredicatable.
Think of somethng like the Hudson crash... imagine a larger impact, more waves, and the tail would have broken off, then sunk. Any buoyancy devices would have dragged the CVR and FDR into the tip of the tail and they would have been dragged down with it.
Most crashes involve high-g impacts and fire, which is what CVRs and FDRs are protected against in the first place. Some do occur over water, which is why there are are ULBs.
CJ
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A CVR/DFDR is located in the rear unpressurized fuselage, mounted on a shelf. ....
Not any more,
It's usually in the rear of the cabin, pressurised, tucked away above the ceiling or in a compartment near the sidewall.
Not any more,
It's usually in the rear of the cabin, pressurised, tucked away above the ceiling or in a compartment near the sidewall.
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DJ
we speak here about the A330 case or not. Actually I'm on duty to monitor them. Full access to AMM/TSM and Airman and all the other nice gizmo programs to monitor. When I post something I refer to a manufacture source:
Statement AMM
The DFDR is installed in the unpressurized area of the rear fuselage and the LA in the center fuselage. LA=Linear Accelerometer
For the CVR I have to correct myself:
To make sure that the CVR has maximum survivability and recoverability:
-
It is installed in the aft section of the aircraft, and
-
It is attached to a rack with two locking tabs.
This one is installed in rear bulk
we speak here about the A330 case or not. Actually I'm on duty to monitor them. Full access to AMM/TSM and Airman and all the other nice gizmo programs to monitor. When I post something I refer to a manufacture source:
Statement AMM
The DFDR is installed in the unpressurized area of the rear fuselage and the LA in the center fuselage. LA=Linear Accelerometer
For the CVR I have to correct myself:
To make sure that the CVR has maximum survivability and recoverability:
-
It is installed in the aft section of the aircraft, and
-
It is attached to a rack with two locking tabs.
This one is installed in rear bulk
Last edited by h3dxb; 6th Jun 2009 at 23:04.
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DJ and h3dxb,
I would have thought my remark still holds...
After a water impact, CVR and FDR would still be just as likely to be tangled in the wreckage as not, no?
Re the A330, the question is obviously moot, since neither would float anyway. We can only hope they broke loose, so there is a chance of hearing the ULB.
CJ
I would have thought my remark still holds...
After a water impact, CVR and FDR would still be just as likely to be tangled in the wreckage as not, no?
Re the A330, the question is obviously moot, since neither would float anyway. We can only hope they broke loose, so there is a chance of hearing the ULB.
CJ
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ChristiaanJ
Re the A330, the question is obviously moot, since neither would float anyway. We can only hope they broke loose, so there is a chance of hearing the ULB.
As you agree the question is moot.
The two solutions are acms transmissions prior to power loss/elec. systems failure or increased ULB transmission capabilities. Seems I expect no FDR recovery in this incident.
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muduckace: "I expect no FDR recovery in this incident."
The U.S. and Egyptian governments spent $17 million to find and recover the Egypt Air B763 recorders [and a fair amount of debris] deep in the North Atlantic. Other successful deep ocean north Atlantic recovery of recorders include that of crashed Air India 747 . . . , not to forget the Titanic; the Thresher and Scorpion subs; the Russian sub in mid Pacific; and two nukes from a crashed B52 in the Mediterranean Sea.
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The ULB's at their current max transmission range are out of range of known detection devices, the aircraft is in pieces. Corpses have floated to surface (their best intel). Just how long did it take us to find the titanic?(A much larger mass of much more interest)
I would bet you a beer on this one.
I would bet you a beer on this one.
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On the likelyhood of DFDR and CVR salvage
This is a repost of my contribution of 3 June to the closed AF447 thread; in the meantime, CNN has mentioned today that the US has offered the Brazialians and the French two TPL's to be operated from French vessels. It won't be easy and the clock is ticking.
"On the likelihood of DFDR and CVR salvage
The Indonesian Adam Air B734 that crashed in the Makassar Strait off Sulawesi on 1 January 2007 had its DFDR and CVR located after 3 weeks at depths of 2000m and 1900m respectively. According to the accident report underwater locator beacon (ULB) signals from the flight recorders were picked up on 21 January 2007 by a US oceanographic vessel Mary Sears and their positions logged.
Just to give an idea of some of the constraints concerning this type of operations, according to the accident report: "Mhe Mary Sears was required to pass within 500 meters of a beacon before it could detect a return. The US Navy Supervisor of Salvage shipped a towed pinger locator (TPL) from Washington, DC, to Makassar. This device is a sonic detector with umbilical cable capable of detecting the underwater locator beacons from the PK-KKW flight data recorder and cockpit voice recorder (if they are still operating), down to a depth of 20,000 feet." The speed with which the TPL was towed through the water was 2-4 kts in the case of the Adam Air B734.
Due to several circumstances (including an initial lack of specialised equipment and disputes about the costs of the salvage operations), the actual salvage started only on 24 August 2007, with the DFDR and CVR being retrieved from the ocean floor by Phoenix International on 27 and 28 August respectively. Functional data were retrieved from both recorders.
Also to give an idea of the specificities of this type of operation, the following text from the accident report: "The underwater survey and recovery used a small ROV, Remora 6000, which was capable of descending to a water depth of 3000 meters. The ROV had three visual cameras and two fixed lights fitted on the front of the vehicle, which were used for visual scanning. The visual range of the camera was about 10 meters. The ROV was also equipped with underwater sonar with good resolution horizontally up to 100 meters. The width of the sonar beam is about 50 meters at a distance 100 meters from an object. The position of the ROV relative to the ship was measured using an underwater positioning system and the ship used differential global positioning system equipment. The coordinates provided by the ship and the ROV were used to mark the location of the aircraft wreckage and these were mapped into a computer. The ROV had a pair of robot arms that were capable of lifting a 25 kg object of a maximum dimension of about 30 cm by 40 cm. The ROV was in the water for about 109 hours and completed five dives."
Although the AF A332 wreckage is arguably at greater depth (between half and double as deep) then that of the Adam Air B734, the above may give an idea of the challenges and constraints of the salvage operations with regard to the AF 332 DFDR and CVR. It would not be impossible though, since the salvage company at the time, Phoenix Intl, states on its website that 6000m is now the max depth of its remotely operated vehicle (ROV), provided of course that the ULB signals are picked up and pinpointed within 30 days."
"On the likelihood of DFDR and CVR salvage
The Indonesian Adam Air B734 that crashed in the Makassar Strait off Sulawesi on 1 January 2007 had its DFDR and CVR located after 3 weeks at depths of 2000m and 1900m respectively. According to the accident report underwater locator beacon (ULB) signals from the flight recorders were picked up on 21 January 2007 by a US oceanographic vessel Mary Sears and their positions logged.
Just to give an idea of some of the constraints concerning this type of operations, according to the accident report: "Mhe Mary Sears was required to pass within 500 meters of a beacon before it could detect a return. The US Navy Supervisor of Salvage shipped a towed pinger locator (TPL) from Washington, DC, to Makassar. This device is a sonic detector with umbilical cable capable of detecting the underwater locator beacons from the PK-KKW flight data recorder and cockpit voice recorder (if they are still operating), down to a depth of 20,000 feet." The speed with which the TPL was towed through the water was 2-4 kts in the case of the Adam Air B734.
Due to several circumstances (including an initial lack of specialised equipment and disputes about the costs of the salvage operations), the actual salvage started only on 24 August 2007, with the DFDR and CVR being retrieved from the ocean floor by Phoenix International on 27 and 28 August respectively. Functional data were retrieved from both recorders.
Also to give an idea of the specificities of this type of operation, the following text from the accident report: "The underwater survey and recovery used a small ROV, Remora 6000, which was capable of descending to a water depth of 3000 meters. The ROV had three visual cameras and two fixed lights fitted on the front of the vehicle, which were used for visual scanning. The visual range of the camera was about 10 meters. The ROV was also equipped with underwater sonar with good resolution horizontally up to 100 meters. The width of the sonar beam is about 50 meters at a distance 100 meters from an object. The position of the ROV relative to the ship was measured using an underwater positioning system and the ship used differential global positioning system equipment. The coordinates provided by the ship and the ROV were used to mark the location of the aircraft wreckage and these were mapped into a computer. The ROV had a pair of robot arms that were capable of lifting a 25 kg object of a maximum dimension of about 30 cm by 40 cm. The ROV was in the water for about 109 hours and completed five dives."
Although the AF A332 wreckage is arguably at greater depth (between half and double as deep) then that of the Adam Air B734, the above may give an idea of the challenges and constraints of the salvage operations with regard to the AF 332 DFDR and CVR. It would not be impossible though, since the salvage company at the time, Phoenix Intl, states on its website that 6000m is now the max depth of its remotely operated vehicle (ROV), provided of course that the ULB signals are picked up and pinpointed within 30 days."
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Fdr Data
My Avionics crew and myself had a interesting discussion on this topic and the best solution we could come up with was a exterior mounted FDR (a slave unite to the FDR the size could be very small, Keep in mind a thumb drive is smaller than the ELT or ULB). It would have a pressure switch to release from the airframe at say 100-200 feet water depth and float to the surface with ULB and ELT transmissions.
Cost is the major factor but would be a solution to the issue we ponder.
Cost is the major factor but would be a solution to the issue we ponder.
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Ejectable Recorder --
Oops, the thread starter was right in my oppinion. I think civil ejectable recorders should be mandated. Solid state memory,a combo ULB/ELT, not really a recorder just a simple memory device.
As far as the ULB reliability goes I believe there has been an AD since then, could be wronge but I have a faint memory of something to the fact.
As far as the ULB reliability goes I believe there has been an AD since then, could be wronge but I have a faint memory of something to the fact.
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All...
Though they don't have FDR or CVR, the Lockheed P3C Orion military airplane carries a self-deployable locator beacon that will separate from the airplane when either one of several mercury bulb crash detectors breaks, or the pilot selects it's release.
It's located in the vertical stabilizer, right side, and is spring loaded into place, and the deployment simply releases the catch and the beacon releases with force (away from the airplane), and is aerofoil shaped to allow it to 'flutter' down to the surface whilst transmitting on both 121.5 and 243.0, which it will continue for several days.
Sounds like a great idea...these were fitted to P3Cs from about the early 1980s.
Cheers...FD...
Though they don't have FDR or CVR, the Lockheed P3C Orion military airplane carries a self-deployable locator beacon that will separate from the airplane when either one of several mercury bulb crash detectors breaks, or the pilot selects it's release.
It's located in the vertical stabilizer, right side, and is spring loaded into place, and the deployment simply releases the catch and the beacon releases with force (away from the airplane), and is aerofoil shaped to allow it to 'flutter' down to the surface whilst transmitting on both 121.5 and 243.0, which it will continue for several days.
Sounds like a great idea...these were fitted to P3Cs from about the early 1980s.
Cheers...FD...
Here you find some details about the deployable recorder installed on the F/A-18:
http://safetycenter.navy.mil/aviatio...loads/FA18.pdf
The expected deployment envelope is enclosed as Appendix B.
Some additional information:
For civil deployable recorders, the following details can be found in EUROCAE ED-112:
The attached ELT must operate for at least 150h.
Of course, an aircraft equipped with a deployable recorder should have an ULB fitted somewhere on the airframe, so that the wreckage can be located if under water.
BR,
aerolearner
http://safetycenter.navy.mil/aviatio...loads/FA18.pdf
The expected deployment envelope is enclosed as Appendix B.
Some additional information:
Deployable Flight Incident Recorder Set (DFIRS)
The DFIRS system consists of the Deployable Flight Incident Recorder Unit (DFIRU), the data transfer interface unit, and the pyrotechnic release system. The SDR consists of the flight incident recorder memory, beacon, battery, and antenna, all contained in an deployable aerodynamic airfoil located on the top on the fuselage between the rudders. DFIRS stores up to 30 minutes of flight incident data and deploys this data along with a rescue beacon, via the airfoil, when activated. The SDR is deployed upon pilot ejection or ground/water impact. The data stored on the flight incident recorder (FIR) is gathered by the mission computer from existing systems on the aircraft. DFIRS records flight data, cautions, advisories, and spin data. The FIR memory wraps around to the beginning when the end of memory is reached. Only the last 30 minutes of each flight is retained. DFIRS data recording starts when both throttles are advanced past 90° power lever angle (PLA), when ground speed exceeds 50 knots, or when WoffW and airspeed is over 80 knots. DFIRS recording stops 1 minute after WOW, both throttles are less than 90° PLA, and the ground speed is less than 50 knots. All data during SPINs and MECH ON cautions are automatically recorded.
The DFIRS system consists of the Deployable Flight Incident Recorder Unit (DFIRU), the data transfer interface unit, and the pyrotechnic release system. The SDR consists of the flight incident recorder memory, beacon, battery, and antenna, all contained in an deployable aerodynamic airfoil located on the top on the fuselage between the rudders. DFIRS stores up to 30 minutes of flight incident data and deploys this data along with a rescue beacon, via the airfoil, when activated. The SDR is deployed upon pilot ejection or ground/water impact. The data stored on the flight incident recorder (FIR) is gathered by the mission computer from existing systems on the aircraft. DFIRS records flight data, cautions, advisories, and spin data. The FIR memory wraps around to the beginning when the end of memory is reached. Only the last 30 minutes of each flight is retained. DFIRS data recording starts when both throttles are advanced past 90° power lever angle (PLA), when ground speed exceeds 50 knots, or when WoffW and airspeed is over 80 knots. DFIRS recording stops 1 minute after WOW, both throttles are less than 90° PLA, and the ground speed is less than 50 knots. All data during SPINs and MECH ON cautions are automatically recorded.
3-1.7 DEPLOYMENT CRITERIA
a. The design characteristics of a deployable recorder shall result in the recorder landing clear of the aircraft wreckage.
b. The unit shall incorporate flight characteristics that enable it to rapidly establish a flight trajectory that clears the airframe.
c. The unit shall not be given sufficient initial momentum on deployment such that its release could endanger ground support personnel or the aircraft itself.
d. Sufficient sensors shall be installed and located to detect impact, and water immersion resulting from an accident.
e. There shall be no means for manual deployment.
3-1.7.1 Impact Initiation
a. Frangible or deformation sensors shall be installed in both the nose and the tail of the aircraft.
b. Sensors may be installed at other locations based on structural analysis and review of typical aircraft crash landing orientations.
NOTE: Impact sensors should be designed such that they will only trigger when the structure has been significantly deformed (representing a catastrophic accident). Negative acceleration sensors should not be used.
3-1.7.2 Hydrostatic Initiation
For both fixed and rotary wing aircraft, a hydrostatic sensor shall deploy the recorder at a depth of 3 m or more.
a. The design characteristics of a deployable recorder shall result in the recorder landing clear of the aircraft wreckage.
b. The unit shall incorporate flight characteristics that enable it to rapidly establish a flight trajectory that clears the airframe.
c. The unit shall not be given sufficient initial momentum on deployment such that its release could endanger ground support personnel or the aircraft itself.
d. Sufficient sensors shall be installed and located to detect impact, and water immersion resulting from an accident.
e. There shall be no means for manual deployment.
3-1.7.1 Impact Initiation
a. Frangible or deformation sensors shall be installed in both the nose and the tail of the aircraft.
b. Sensors may be installed at other locations based on structural analysis and review of typical aircraft crash landing orientations.
NOTE: Impact sensors should be designed such that they will only trigger when the structure has been significantly deformed (representing a catastrophic accident). Negative acceleration sensors should not be used.
3-1.7.2 Hydrostatic Initiation
For both fixed and rotary wing aircraft, a hydrostatic sensor shall deploy the recorder at a depth of 3 m or more.
Of course, an aircraft equipped with a deployable recorder should have an ULB fitted somewhere on the airframe, so that the wreckage can be located if under water.
BR,
aerolearner
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Another Angle
I don't think that ejecting the FDR/CVR is the answer to this problem. Though a datalink to the Airline or Manufacturer is probably not feasible because of the bandwith requirments, I would suggest the following:
If an aircraft crashes, there should be a way to trigger a download of the FDR/CDR contents over some kind of RF transmission. Each CVR/FDR should have a unique code to trigger the download. For Deep Water Crashes, the technology exists to transmit data over ultrasonic pulses. If the Ultrasonic Beacon can be heard, then too could the data be downloaded over ultrasonics. This method may be more difficult for non-digital recorders, but should be pretty simple for the digital ones. The transmissions could be scrambled to restrict access from Hackers.
Yes, the most desirable situation is for the NTSB to get their "hot-little-hands" on the orange boxes. But this would be the fail-safe... Though it may not always work, it extends the possibility of retrieving this important data one more level.
If an aircraft crashes, there should be a way to trigger a download of the FDR/CDR contents over some kind of RF transmission. Each CVR/FDR should have a unique code to trigger the download. For Deep Water Crashes, the technology exists to transmit data over ultrasonic pulses. If the Ultrasonic Beacon can be heard, then too could the data be downloaded over ultrasonics. This method may be more difficult for non-digital recorders, but should be pretty simple for the digital ones. The transmissions could be scrambled to restrict access from Hackers.
Yes, the most desirable situation is for the NTSB to get their "hot-little-hands" on the orange boxes. But this would be the fail-safe... Though it may not always work, it extends the possibility of retrieving this important data one more level.
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adoiyaircraft:
Nice idea, but it won't work. You need somone to receive the sonar data you've transmitted. It will be detectable at about the same range as the pinger, or (probably) a shorter range. So if we can't find the pinger, we certainly can't get the data stream. (I design systems of this type for a living, BTW).
Not sure what you mean by RF transmission - the ACARS is the RF tx we use right now. Or do you mean a panic-mode download of data after an incident has started? Often that won't work (because the aircraft is in bits by the time you have data to send).
'Hard cases make bad law' as they say - the AF447 is just about the worst possible case - very deep water, Southern hemisphere (fewer deepwater resources available), developing nation involved, poor position reporting...
I'd like the pingers to use a lower frequency (to give longer range - maybe 5kHz rather than 37.5kHz?), and save power by transmitting only 1/4 of the time (or at 1/4 the ping rate) - this would give 4 months to get resources on site to do detection/recovery. (...But I'm guessing that nobody cares what I think about that...)
The deepwater ROV/salvage capability exists to recover wreckage and recorders, if someone's willing to foot the bill. AF447 can almost certainly be found, too, even without the pingers, if someone's willing to pay. Lots of people do very deep water (ie full ocean depth, 6km) sidescan sonar searches for shipwrecks. The precision survey work done in deep water for the oil and gas industry would blow your mind. Finding an aircraft or fragments of one can be done using this approach - but it takes more $$ the smaller the pieces you're looking for.
Regarding ejectable devices - we'd have to be super-duper confident that in the worst case (ie the AF crash) the device would be ejected successfully. If not, you've spent a bunch of money equipping the fleet with something which has contributed nothing to safety. The ejectable device would be required (ie black boxes would not be recoverable) maybe once every 20 years?
I'd prefer to see money spent on getting realtime satellite imagery into the cockpit, so that no plane I'm ever on goes anywhere near any thunderstorms.
Nice idea, but it won't work. You need somone to receive the sonar data you've transmitted. It will be detectable at about the same range as the pinger, or (probably) a shorter range. So if we can't find the pinger, we certainly can't get the data stream. (I design systems of this type for a living, BTW).
Not sure what you mean by RF transmission - the ACARS is the RF tx we use right now. Or do you mean a panic-mode download of data after an incident has started? Often that won't work (because the aircraft is in bits by the time you have data to send).
'Hard cases make bad law' as they say - the AF447 is just about the worst possible case - very deep water, Southern hemisphere (fewer deepwater resources available), developing nation involved, poor position reporting...
I'd like the pingers to use a lower frequency (to give longer range - maybe 5kHz rather than 37.5kHz?), and save power by transmitting only 1/4 of the time (or at 1/4 the ping rate) - this would give 4 months to get resources on site to do detection/recovery. (...But I'm guessing that nobody cares what I think about that...)
The deepwater ROV/salvage capability exists to recover wreckage and recorders, if someone's willing to foot the bill. AF447 can almost certainly be found, too, even without the pingers, if someone's willing to pay. Lots of people do very deep water (ie full ocean depth, 6km) sidescan sonar searches for shipwrecks. The precision survey work done in deep water for the oil and gas industry would blow your mind. Finding an aircraft or fragments of one can be done using this approach - but it takes more $$ the smaller the pieces you're looking for.
Regarding ejectable devices - we'd have to be super-duper confident that in the worst case (ie the AF crash) the device would be ejected successfully. If not, you've spent a bunch of money equipping the fleet with something which has contributed nothing to safety. The ejectable device would be required (ie black boxes would not be recoverable) maybe once every 20 years?
I'd prefer to see money spent on getting realtime satellite imagery into the cockpit, so that no plane I'm ever on goes anywhere near any thunderstorms.
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Still Another angle
I am not talking about the CVR/FDR transmitting upon impact. What I am suggesting is that once the Officials reach the sight, they can transmit a "Trigger" signal that only the target CVR/FDR pair will respond to. If the Airplane is in deep water, there will be ships searching for the beacon. Once they locate the beacon, they transmit the command to the CVR/FDR to begin the ultrasonic data transmission, and collect the data from aboard ship. If an airplane crashes in the Andes, or some unreachable location, a search aircraft, flying overhead, could transmit the download command for the CVR/FDR to transmit the data over a radio frequency that then would be collected from the air. The trigger codes would be unique to individual FDR/CVR and would be maintained in the aircraft maintenence records or some other database.
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The problem isn't recovering the recorders when they're underwater, it's finding them (there's always some sort of ROV or submersible that can get to the wreckage). So all the battery power available should be used for the pinger (beacon), not for data transmission.
Also, the data rates for sonar data transmission are really, really low (and we're talking sonar, not ultrasound, which is much higher frequency, but won't travel more than a few feet). Like hundreds of baud, if you want to be confident that the message has been received at the surface. It would take tens of hours to download the CVR/FDR contents using acoustic means (think: huge amounts of battery power), and there's a good chance you'd lose some data; and some significant percentage of the time, the complex data transmission system wouldn't work at all (vide the difficulty in just finding the recorders from AF447). It's just not a cost-effective way of spending money on safety.
Same thing applies to RF transmission - you're making a whole bunch of assumptions about where the recorders are & that the data signals can make it to the overflying aircraft. There's no location that I can think of where it wouldn't be less problematic to just pick up the boxes. You're always going to put some sort of crash investigation team on the ground, anyway. Use battery power for RF locator beacons, not data transmission.
Also, the data rates for sonar data transmission are really, really low (and we're talking sonar, not ultrasound, which is much higher frequency, but won't travel more than a few feet). Like hundreds of baud, if you want to be confident that the message has been received at the surface. It would take tens of hours to download the CVR/FDR contents using acoustic means (think: huge amounts of battery power), and there's a good chance you'd lose some data; and some significant percentage of the time, the complex data transmission system wouldn't work at all (vide the difficulty in just finding the recorders from AF447). It's just not a cost-effective way of spending money on safety.
Same thing applies to RF transmission - you're making a whole bunch of assumptions about where the recorders are & that the data signals can make it to the overflying aircraft. There's no location that I can think of where it wouldn't be less problematic to just pick up the boxes. You're always going to put some sort of crash investigation team on the ground, anyway. Use battery power for RF locator beacons, not data transmission.
