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Black Box Flight Data Recorder

06/05/2009 7:03 AM

Air flight recorder when immmersed in water uses Ultrasonic locaton Beacon by which one can easily determine the location of the plane

What makes the finding of the black box difficult , considering the present unfortunate event in south atlantic

Regards

Jose

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#1

Re: Black Box Recorder

06/05/2009 7:34 AM

Probably 7,000 meters of water depth and a huge surface area to search just to determine the approximate impact zone.

I don't recall the pinger's SPL, but it only has so much acoustic energy and can't always be heard when you would think it should and has limited range and duration. The acoustic output frequency is ultrasonic, way above hearing, which helps distinguish it from background noise.

First, the ocean water is not homogeneous. So, sound does not propagate uniformly across the ocean. Thermal layers of water that stratify the ocean, called thermoclines, act like acoustic mirrors and reflect sound away from the layer. Hearing the pinger may not be easy or even possible in some cases.

All of this assumes that the black box is even working or not burried under the aircraft wreckage or sea floor.

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#3
In reply to #1

Re: Black Box Recorder

06/05/2009 8:28 AM

A question arises in my mind, What if we fix a radio frequency transmitter High power enough, but transmit in the form of impulses ( say for 1 microsecond for every second). using impulses can improve battery life even at reasonably high power. fixed inside black box and activated as soon as plane crashes.

Just a thought

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#8
In reply to #3

Re: Black Box Recorder

06/05/2009 10:41 AM

It's a good question.

RF has a nasty time transversing through water. The higher the RF frequency the shorter the path through water it can travel.

The US Navy (and others) have used, and I believe it is still in service, very powerful land based RF transmitters running at extremely low frequency (VLF Comm). With this system they can send one-way messages to submarines that are submerged.

The problems with the system is that it requires a lot of RF power, very large antenna arrays, and the encoded data rate is laboriously slow.

As you may be aware, the lower the frequency of a wave the less data that can be carried on that wave.

Even at that, the depth that VLF RF can penetrate is less than 100 meters.

The VLF communication system really just tells the sub commander, "Hey, you got mail!" At which point the sub goes to a depth that they can jab an antenna above water and use a more reliable communication frequency.

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#9
In reply to #8

Re: Black Box Recorder

06/05/2009 10:44 AM

I was actually patting you on the back for knowing about thermoclines and the effect on sound propagation - but that is more than I knew about the ULF systems.

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#13
In reply to #9

Re: Black Box Recorder

06/05/2009 7:13 PM

Thank you very much.

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#23
In reply to #8

Re: Black Box Recorder

06/07/2009 9:06 AM

Hi thank you for nice answer.

Even at that, the depth that VLF RF can penetrate is less than 100 meters.

Thats the reason I was talking RF in impulses, lets say if we throw impulse of 1 microseconds for every seconds, this will enable designer to push 1000times power in transmitter,even with the same size of a battery and also the size of electronics can be reduced significantly as it will produce much lesser heat in each second.

I mean that 100 meters can increased to 100*1000=100km,of-course with the less amount of info.

the only question that need to be asked is how much info can we send in each microseconds?

Thanks

Regards

RS

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#7
In reply to #1

Re: Black Box Recorder

06/05/2009 9:44 AM

good job, AH

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#2

Re: Black Box Recorder

06/05/2009 7:37 AM

Access to it. Reportedly it is in very deep water, and there are only a few vehicles that con go that deep. Further, the vehicles have to be available, and have to be brought close to the site. Further, the site has been difficult to find; reportedly the debris that has been found up to 5th June is general trash ('"Throw it away"? There is no "away".' ) and not aeroplane contents.

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#4

Re: Black Box Recorder

06/05/2009 8:28 AM

The "Black Box" FDR/CVR locator beacon which is known as the "pinger" transmits an acoustic signal at 37.5 Khz and can be detected by a special receiver. The FDR/CVR can be retrieved as long as this "pinger" is still intact on the FDR/CVR. But there is always a chance that the "pinger" can separate from the FDR/CVR in case of high impact. The pingers can nominally be heard for about 2 miles. At an ocean depth of about 8,000 feet and 12,000 feet, it would be pure luck to drop a monitoring buoy with special receiver in a position where it heard a pinger, given the depth. At the surface, the radius of success is substantially smaller than 2 miles.
The distance the pinger can be heard will also be affected by any thermal layers in the ocean, and the terrain where the FDR/CVR came to rest, both reducing the range. Towed sensors working below the surface improve the coverage pattern. Here's the general specs for the FDR/CVR;

Flight Data Recorder
Time recorded = 25 hour continuous
Number of parameters = 18 - 1000+
Impact tolerance = 3400Gs / 6.5 ms
Fire resistance = 1100 degC / 30 min
Water pressure resistance submerged = 20,000 ft
Underwater locator beacon = 37.5 KHz; battery has shelf life of 6 years or more, with 30-day operation capability upon activation

Cockpit Voice Recorder
Time recorded = 30 min continuous, 2 hours for solid state digital units
Number of channels = 4
Impact tolerance = 3400Gs / 6.5 ms
Fire resistance = 1100 degC / 30 min
Water pressure resistance submerged = 20,000 ft
Underwater locator beacon = 37.5 KHz; battery has shelf life of 6 years or more, with 30-day operation capability upon activation

The ULB, also known as the "pinger" usually have the following specifications
Underwater Locator Beacon (ULB)
Operating Frequency:37.5 kHz ± 1 kHz
Operating Depth:Surface to 20,000 feet
Pulse Length:Not less than 9 milliseconds
Pulse Repetition Rate:Not less than 0.9 pulse per second
Useful Life:Six years
Operating Life:30 days (minimum)
Acoustic Output, Initial:1060 dynes/cm2 rms pressure at 1 meter (160.5 dB)Acoustic Output, After 30 days:700 dynes/cm2 rms pressure at 1 meter (157.0 dB)
Operating Temperature:28º F to 100º F
Actuation:Fresh or salt water, surface to 20,000 feet
Radiation Pattern:Rated output over 80 percent of sphere

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Anonymous Poster
#32
In reply to #4

Re: Black Box Recorder

08/01/2009 10:59 AM

This is a very informative post as to the specs of the beacon transmitters. I wish some one would post something on the receiving equipment available to receive the signals. What is the most sensitive receiver and which ones can operate at that depth? A lot of ocean going ships have depth recorders operating between 35.0 and 40.0 KHz and they would probably get a vertical line on their recorders as the 37.5 KHz pings are received but directly over the beacon they are well out of range of the beacon transmitter.

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#33
In reply to #4

Re: Black Box Recorder

04/05/2014 2:39 PM

Hi,

Reading this post with interest as many of the posts are very well informed. The pinger uses low levels of electrical power to provide enough acoustic energy to be detected in most ocean depths. The electrical power to produce this acoustic ping is less than 0.5W for 10 mS in every second i.e., the average power of transmission is 0.005W + the signal generation and control power which is likely to double the above in total. The design of the pinger does assume the location of the aircarft is known, in this case it will be very difficult to find the pinger in deep water and high sea states affecting the signal to noise ratio of the receiver equipment.

The best chance to find the pinger is the British T boat, it has dirrectional arrays covering 360 degrees so can scan a large area in a relatively short time and it can go deep and at a reasonable speed (flow noise will increase but not as much as a surface ship).

The towed arrays are a waste of time as the ship can only go at 4Knots or it will make so much noise the receiver will not pick up the pinger and the towed body will come closer to the surface due to hydordynamic drag (and get thrown around in the prop wash). The tow fish or ROV (sidescan sonar called Bluefin) will come into their own if and when the plane is located which may be never, they may be better off with mine hunting ships using multibeam Sonar like S20194 (UK).

The problem with so many assets including ships and planes etc they will make it more difficult for the submarine detection equipment as the background noise level will increase also towing objects with a submarine in the area is not a good idea.

A good point was made in an earlier post if the plane did not break up e.g., the plane landed on the water and then sunk (as there is no wreckage) then the pingers are still in their racks this could prevent the ping penetrating the aircraft structure though the insultion operating at 38kHz.

The range of the pingers is less than 2km in free water at sea state 2 with a pulse envelope of 10mS the 1/T component can be detected up to 8km (100Hz) or more as it brings in the large low frequency arrays of the submarine.

The pinger is very crude device and should be updated, I worked on a project which included a lost towed body pinger which only pinged when pinged at with a coded signal. This solution lets the pinger save it's battery over the 6 year shelf life i.e., it operates like a car key fob where the indicater flashes when pinged. The other advantage of this method is the pinger could put out a much higher source level to make detection easier. The down side is you need a special transmiter on the surface ship but at least there is a good chance of detection. This project did not see the light of day as we lost the proposal as it was too expensive!

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#34
In reply to #33

Re: Black Box Recorder

04/08/2014 8:46 AM

Following my last post I find it unbelievable the Australians have located the pingers so quickly with the equipment the are using i.e., in deep water of 4500m with the pinger range of 2.5Km at sea state 5 or 4km at sea state 2 implies calm seas and being extremely lucky or they knew where the aircraft crashed probably using recorded military sat data. To pick up pings for 17 minutes at 2 Knots means (1.1m/s) they picked up the pings of 350m distance! in other words they are almost directly over the aircraft, if the crew knew what they are doing they should cross the middle of this line at 90 degrees from 2km so they can work out where the aircraft is with reasonable accuracy. Using this method, if they get pings over 1Km then the aircraft is 500 m from where they lose contact and on the same bearing. The news showed an FFT history output for each ping so they can gather amplitude data of each ping also helping to locate the aircarft.

The China ship detections I suspect is probably a touch of propaganda or not being able to use the equipment also they were on the surface with their array, it is unlikely the signal would reach the surface.

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#5

Re: Black Box Recorder

06/05/2009 8:30 AM

"which one can easily determine the location of the plane"

oh, really ?

great answer Aussie Bob

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#6

Re: Black Box Flight Data Recorder

06/05/2009 9:19 AM

High frequency transmissions are short lived in water. The low frequency ELF transmissions used to contact submarines needs an excessively long antenna that trails behind the sub at specific times for contact, and needs longer times to complete a transmission. Whether that type of transmission could be used as a locater or not (GPS connected to last known position), ?

I think perhaps transmission of black box data should begin at the moment of the catastrophic failure of any critical component. Burst transmitting both last known position and systems data. After all, 20,000 feet is a long way to fall, and time enough to keep updating until impact. Or am I missing something here?

I think the failure will be found in habitualy 'pencil whipped' inspection sheets.

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#10

Re: Black Box Flight Data Recorder

06/05/2009 2:54 PM

The Atlantic is very big and very deep.
Even if you locat it...if it's 2 miles down you will have a problem.

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#11
In reply to #10

Re: Black Box Flight Data Recorder

06/05/2009 3:18 PM

why not put the FDR embedded in a floatation device that resist high temperature & light enough to float?

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#12
In reply to #11

Re: Black Box Flight Data Recorder

06/05/2009 3:21 PM

Funny you should ask!

about 3/4s of the way through there is a similar discussion!

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#14
In reply to #11

Re: Black Box Flight Data Recorder

06/05/2009 11:06 PM

At the pressures encountered at -5,000 feet, or even -1,000 feet, whatever air is trapped in the system is squeezed into such a small volume that it represents a zero sum gain. Ya can't float a rock with a thimble. Relativity Rules. Air however, can be replaced with an empty hard tank. Volumetrics sez 'up'. Now: someone is going to challenge this. That's why we're here. Dump ballast, see sunlight, transmit.

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#15

Re: Black Box Flight Data Recorder

06/06/2009 12:36 AM

Big ocean, deep water, little boxes...

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#16

Re: Black Box Flight Data Recorder

06/06/2009 4:19 AM

I find it strange that an aircraft sophisticated enough to telemetry fault data through satellite comm's cannot transmit GPS data through the same link. If such a system was in place then at least they would know the location where the faults caused the aircraft to descend. For years we have used GPS to dynamically position ships, so why are we still relying on radar for aircraft position.

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#31
In reply to #16

Re: Black Box Flight Data Recorder

08/01/2009 10:33 AM

If it can not even get the pinger receive I doubt that anythinc will be received.

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#17

Re: Black Box Flight Data Recorder

06/06/2009 2:07 PM

I can only assume that depth in water presents many obstacles, and depending on how a plane goes down, whether it exploded in air, the force it or the pieces of it hits the water, the way it disperses in the air and parts are displaced in the water due to currents, etc. it can be very hard to locate. Any signal emitted from a black box is also subject to dissipation, through still water alone much less the powerful currents in an ocean far off land.

The point of impact means little depending on what part of the ocean, what size plane it was, and what portion(s) of a plane are still intact.

The costs of such a tasks are heavy, and it usually means at certain depths that human diving is not an option, and expensive equipment and submarines whether large or small most likely will be utilized.

Any beacon going off in those depths to me may giving off ghost images everywhere, bouncing off surfaces, schools of fish, still subject to currents, and I can only guess that the whole operation is time sensitive, who knows how long such a signal (assuming that it is working at all, we all have heard of the durability of black boxes) would still be able to transmit under such pressures, temperatures, etc.

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#18

Re: Black Box Flight Data Recorder

06/06/2009 8:42 PM

Black box sounds like an outdated technology to me.Why not transmit the same data continously in real time? The info could be erased if the plane lands without incident, so long term storage is not a problem.The plane sent 24 messages automatically, why not transmit all the data that was stored on the black box starting when the first alarm activated? Finding the black box would then be redundant unless the transmission failed.

Any reason, besides $$$$ this is not possible or practical?

HTRN

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#19

Re: Black Box Flight Data Recorder

06/06/2009 8:45 PM

Imagine yourself in the middle of the ocean, screaming at the top of your lungs.A mere speck in thousands of square miles of empty water.Would your location be easy to find?

A very small needle in a very large haystack.

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#26
In reply to #19

Re: Black Box Flight Data Recorder

06/07/2009 10:33 AM

Good question.

I often find myself working on the back deck of oceangoing vessels. My personal life jacket contains a SAR-SAT locating device. Using satellite positioning technology, this device can enable the SAR-SAT monitoring facility to automatically pinpoint my location in as little as twenty minutes. An online database that I keep up to date will direct the monitoring facility to contact my vessel's bridge and notify them of my current location. It also contains a submersible VHF radio that would allow me to hail the bridge myself. Expensive but I believe it was money well spent. I possessed one of these devices for years and have not (and hopefully) ever been in a situation where I needed to use it's SAR-SAT function.

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#20

Re: Black Box Flight Data Recorder

06/07/2009 7:03 AM

As was previously stated, the pinger has a limited range; probably around 1500 meters or so. In addition, there are three distinct temperature layers in the ocean ; diurnal, seasonal, and permanent thermoclines These temperature inversion layers tend to reflect ultrasound and can impede the return of the acoustic pulses to the surface. The greater the net change in temperature, the greater the reflection coefficient.

So, in order to find this pinger, a buoy would need to be dropped into the water. But, where should one look? The best way to search for the location of the wreckage would be to conduct a regional sidescan sonar survey. I would also include a total-field magnetometer in the survey .

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#21
In reply to #20

Re: Black Box Flight Data Recorder

06/07/2009 7:20 AM

Time to bring in the P-3s!

Except I don't know if sonobuoys reach into the same ultra-sonic freqs (easy enough to find out) and don't know if there iis enough steel (ferrous material) in an airliner to find with magnetic detection gear.

So maybe NOT!

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#22
In reply to #21

Re: Black Box Flight Data Recorder

06/07/2009 8:36 AM

There may not be enough ferrous materials but, I'd deploy one anyway. A survey of the debris field would be required in order to plan a retrieval with a ROV.

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#24
In reply to #21

Re: Black Box Flight Data Recorder

06/07/2009 10:06 AM

Hi Ed, For a lack of a better term, I used ultrasound simply to identify the frequency range that acoustic pingers normally operate in. Granted, there are pingers that operate below the ultrasound band of frequencies, but they require large amounts of power; not normally available in a battery-operated device.

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#25
In reply to #24

Re: Black Box Flight Data Recorder

06/07/2009 10:13 AM

gotcha

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#27

Re: Black Box Flight Data Recorder

06/08/2009 1:44 AM

I recall that some years (decades?) ago there was a crash at sea and the recorders were retrieved from a surprising depth, after a couple of weeks search. The circular error probable as well as the depth may have been considerably less than reported ranges for AF #447. Nevertheless, it would be interesting to recall the details. My search of the Internet has so far been fruitless. Anyone else? --Old guy

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#28
In reply to #27

Re: Black Box Flight Data Recorder

06/08/2009 3:48 AM

Are you perhaps thinking of the South African Airways flight 295. They found the voice recorder long after the pinger had stopped functioning, but never found the data recorder. Depth was around 5000 m.

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#29
In reply to #28

Re: Black Box Flight Data Recorder

06/08/2009 4:43 AM

Prof, good sleuthing, although as a South African, you have the advantage on me. This could be the flight, although my likely faulty memory had it that for the flight and search that I (thought I) remembered, a pinger was working. Anyway, sonar at 5,000 m. seems impressive to me. I remain optimistic that they will come up with something on #447, despite the daunting constraints.

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#30
In reply to #29

Re: Black Box Flight Data Recorder

06/08/2009 8:39 PM

Ta, no sleuthing required, the Helderberg is burnt deep into the old memory - had friends on board and there were (and still are) many conspiracy theories surrounding the crash. It was in a sad period in our history and the theories varied from weapons to fireworks in the hold (amongst others).

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