I see I need to read up on underwater sound, since yuo mention "line of sight".... Are any of the parameters for the medium, wavelength, transmission, diffraction, etc. at all comparable with light or radio waves in air?
Wouldn't the distance measurement be only very approximate? It's not a transponder system, so the only clue is the "ping" strength.

CJ

No, not at all.

If you're after a crude analogy then sound propagation through air is better one.

Just another idea...
 

Do passive locator systems such as RECCO (for finding skiers caught in avalanches) function underwater? If such a system could be developped, and assuming the cost / size was reasonable, such "tags" could be incorporated into many of the aircraft parts. This would no-doubt increase the chances of locating an aircraft / debris field in circumstances such as this.

The maritime equivalent would be the combined EPIRB+voyage data recorder. The engineering would need to be substantially different as the worst they will need to survive is something like a 35m drop test into water.

In terms of energy budgets, any device that is not related to distress alerting ie the FDR/CVR would be better as a transponder only. There is no point in transmitting 'blind', wait until you know someone is actively looking before using any energy reserve.

RF transponder tags like RECCO are 'powered' by the received RF energy and are only effective over very short distances (metres) at the frequencies used, this would be cm in water.

The listening device has at least 2 detectors positioned very close together, but far enough apart that there is a time difference in receiving the reply signal. Using very clever signal processing, the distance and angle can be calculated, to within a few centimetres over a couple of kilometres.
IIRC sound travels about 3 times as fast in water as in air. I don't know all the theory and it would no doubt occupy a large amount of space to explain it all here.

the speed of sound in water (and in air too, to a lesser degree) is intensely variable with factors such as salinity,depth, adjacent layers and such.

it is possible that you could be a few hundred feet away and miss sounds channeled away below. Some advantage could certainly be gained by varying the frequency (pitch) of the ping depending on depth,etc but would be very expensive with very little attributable value.

Best scenario I think would simply be saturating the earth and oceans along the flight path with relay stations (think cell towers) which could capture regular broadcasts (not satellite) of ACARS like information.

The cost of maintaining this network would be offset by having them serve some dual purpose (i.e. we already have ultra sound weather buoys to capture water temperature, weather data etc.)

Multiple FDR?
 

In general, an aircraft carries a single FDR, built and armoured to withstand very high deceleartions and intense fires. It is also located within the airframe in a position where it is likely to remain in the main debris field following any impact.

With modern technology would it not be possible to install several light-weight FDRs, not so heavily armoured or fire-resistant, in structural elements such as the fin or wingtips that are likely to break off in a catastrophic impact, and end up in the outer fringes of the debris field, or even float in the case of a break-up on impact with water.

It should be possible to construct such a recorder with a form factor similar to a mobile phone and with similar power requirements. It could even be fitted with an RFID tag to aid in location.

I'm not suggesting that these mini-FDRs (and CVRs) should replace the current concept, but a lightweight recorder at the top of the fin could have told us much more than we might ever know now about the final minutes of AF447.

Be a lot simpler if the aircraft itself routinely transmitted a signal with location co-ordinates, that would generate an alarm if signals were not recieved at 'home'

Last signal = last known location = where to start looking.

You would also be able to work out speed and heading from the previous transmissions so you could search in the right area.

This might provide a better guide to finding the recorders than following floating wreckage and best guesses.

Some recent posters, please read this.... and think about it.

CJ

Hi,

From far far readings months ago (at the beginning of the AF447 drama) it was noticed this plane was equipped with some kind of EPIRB but they do not function AKAIK by what was posted in this forum times ago.
Methink it's a legal requirement for have this kind of EPIRB aboard airliners.

The maritime example of EPIRB+VDR was just for comparison. In terms of SAR the required device would be best equipped with a radar transponder (SART). As CJ pointed out, having the exact GPS distress location at sea will give you an exact idea of which SAR unit to scramble but not necessarily exactly where to look. Without either continuously updated GPS coordinate transmission or a SART the search is less likely to give a positive result.

In the maritime field such equipment exists but there would need to be extensive engineering research to ensure survivability and operation in such a case as we have here.

What about alternative detection methods; if a number of strong magnets were dispersed around the airframe (but away from the cockpit to avoid interference with instrumentation), then it is possible that MAD detectors might pick them up (with no power source required).

Just wanted to clear up some points in this thread however am very limited what I can say for now.

There is no problem with the avaliablity of the equipment to undertake this workscope. There are a number of suitable vessels currently idle with 4000m rated WROV's spreads on board and ready to go. There are only a handful of suitable deep tow side scan sonar systems around but such a system is indeed avaliable right now. Basically there are no 'equipment issues' causing these delays, I could have a vessel fully mobbed and ready to go in 10-14 days.

The technology above stands a very good chance of finding the boxes, I have seen the resolutioin that this sonar system produces and trust me it can find very small items down to 6000m. Temperature layers are also not a problem, the sonar fish is flown 100m or so above the surface of the seabed and covers a very wide swath, the main problem being the terrain it will need to be flown over.

@UA
Juste wondering if you could comment about the order of magnitude of the cost involved in operating such vessel ? Also what would be the typical mission for this type of equipment ? Telecom cables ? (very) deep offshore rigs ? scientific ?

@UA
I don't know either, whether you can comment on some of the issues?

Do we even know where the debris field is?

What's the resolution of the sonar? How easy or difficult is it to distinguish a piece of 'man-made' debris from the rock next to it?

It's unlikely the FDR and CVR were thrown clear from the rest of the wreckage... more likely they're still stuck in some of the aircraft structure. So much the same question... you're not looking for rectangular boxes, but for the most likely parts of the wreckage. Can the kind of sonar you mention find those?

You obviously would not send a ROV down until you had at least some kind of target, no?

CJ

No, and they sometimes don't function under several feet of snow, depending on the attitude of the slope, wetness of the snow, so forth.

Any beacon signal is a last-ditch effort - broken beacon, unfavorable conditions.

Seriously -

Having a transponder detach from a frame is only good in a military situation where you can assume several other craft will be in the same general area and can actively locate the transponder.

Trying to transmit all the parameters recorded by the recorder(s) is a nice idea, but unrealistic at this point mainly due to cost. Unrealistic also considering bandwidth - not that a "perfect" connection would not be able to transmit all the data, but assume that an imperfect connection would not be able to transmit enough of it faithfully.

What could be done is this - very short bursts of data which include indicated position and perhaps GPS position, transmitted every 2 - 5 minutes.

Just having that data would reduce the search area tremendously. If you used 2 minutes as the design "center" value, then you'd be able to tell within a few dozen miles exactly where a flight stopped relaying data, and from that you could narrow the search area greatly, perhaps to less than 100 miles.

The "guess" zone for 447 was huge initially, and was eventually refined to another "guess" based on ocean currents, but the true location hasn't been pinpointed yet.

If one could have started the search assuming 100 mile accuracy, the boxes might be in the lab by now.

Point being, it's not so much what you transmit, it's where and when you transmit.

ACARS hasn't been too much help. The pingers on the outside of the boxes haven't been too much help.

What would have really helped would have been a simple lat+long from the aircraft, updated for as long as possible, even transmitted through ACARS.

406Mhz ELT's are usually installed on any large transport these days. No idea if thats what the AF had fitted but certainly what BA uses.
The have a foam float around the unit but for it to be effective it first needs to break free from the fuselage and reach the surface.

How about a frangible, or even soluble part of the fuselage that releases a photoluminescent dye ?? Even if currents move it would give you a very good idea, and very quickly where the wreckage was.

Would also cost a pittance.

Or even yellow plastic ducks?

You can see my dye by satellite :)