Air Canada (TCA)  DC8 Flight 831, dove vertically into a swamp in Quebec in 1963. Despite driving steel piles and excavating to about 40' depth, nothing of great significance was found.

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It would be interesting to see the Cargo Manifest for Malaysian FL 370.

One wonders if there were any very high value shipments- such as gold bullion, diamonds or pharmaceuticals.

Any of which perhaps, mysteriously, did NOT actually get loaded onto FL 370 and equally mysteriously disappeared from the air cargo facility.

A subsequent, unexplained aircraft disappearance would conveniently hide such an event.

january

I asked the same question,what was on the cargo manifest!

There would be very little debris if the pilot attempted a controlled ditching.

If this flight was "CONTROLLED", why was it in the "middle" of the Indian ocean? Lots of flight paths would have taken it to land somewhere. A turn easterly earlier would have allowed an Australia destination before empty tanks

If a suicide situation, why wait till fuel runs out with the risk of a soft landing and not killing oneself.

IF FL 370 is really where the present searchers think it is, the odds are that all aboard were then dead or unconscious before impact.

I'm inclined to think the plane is somewhere else, despite apparent pings. Orca (Killer Whale) researchers have studied/recorded remarkable conversations amongst these creatures.

january

You go Jeff ... (really enjoy his insight from a real pilot ... especially his CNN comments)

 

 

Cheers, Rob.

More underwater pings heard in hunt for plane: http://hosted.ap.org/dynamic/stories/A/AS_MALAYSIA_PLANE?SITE=AP&SECTION=HOME&TEMPLATE=DEFAULT&CTIME=2014-04-08-23-49-23

 

Prayers for all the families and huge thanks to the searchers, doing their best.

Here's a puzzle.

In an article on Bloomberg News, the manufacturer says the aircraft pingers have a range of about 2 miles ( or approx 10-11,000 ft.)

Yet the water depths in the search area are said to be approx. 14,000 ft.

Does that imply that the pinger locater is towed on a tether exceeding considerably, 3000 feet in length?

january

Does that imply that the pinger locater is towed on a tether exceeding considerably, 3000 feet in length?

 

They have a range of up to 20,000 feet depth and they are towed behind a surface vessel to 1000 feet above the ocean floor:

http://en.wikipedia.org/wiki/Towed_pinger_locator

That means a tow line of perhaps 20,000+ ft to get the hydrophone down to near bottom  where this search is occurring !! (The tow line forming a very long catenary arc behind the ship.)

No wonder the search seems so slow- the tow vessel having to turn on a very wide arc or else reel in the tow before turning.

Probably the latter to avoid the hydrophone sinking to the ocean floor during turn.

No wonder the process is slow. 

january                           

 

 

That means a tow line of perhaps 20,000+ ft to get the hydrophone down to near bottom where this search is occurring !! (The tow line forming a very long catenary arc behind the ship.)

 

I used to be in this business (search and recovery, acoustic engineer, sonar, etc.). The pinger locator that has been shown on TV provided by SUP SALV is a light weight unit that creates "dive force" by the way it is configured once attached to the tow cable. The result is that forward movement causes the tow body to dive.

 

We use a roughly 3 : 1 cable length to depth ratio to calculate the approximate total cable length required for a given depth. For example, if you had a 100 meter depth, you would need 300 meters of cable. A 10,000 foot depth would require a 30,000 foot cable (again, as an approximation - there are other factors that can drive length requirements). In this case, at 15,000 feet, that results in a 45,000 foot cable. The winch required to deploy and haul in that much cable would be huge.

 

However, that tow shape does not have the "horse power" to get the tow body anywhere near that depth and with that length (and weight) of cable. And, more importantly, if that tow package is a typical pinger locator, it would be crushed before it came anywhere near close to that depth. Most locators I have used or been exposed to do not have anywhere near that depth capacity.

 

The good news however is that pinger detection distance is not an exact science and in fact is dependent upon so many variables that no one can say for sure at what distance that pinger will be detected at in any given moment. In  fact, a ping can be heard one moment and disappear the next (just as it has seemed to happen in this case). Slant range, thermoclines, pinger locator sensitivity, all come into play. The most important of these is the thermoclines. Favorable will result in the pinger being detected miles away. Negative will result in you not being able to detect it down the block, so to speak.

Thanks Tom- most interesting. My experience in this type of endeavor is limited to towing a lure for salmon from a 33' sailboat, at depths of perhaps 50' to 100'  - in the waters near Vancouver Island. 

Even that, gives me an appreciation of the difficulties of current efforts, in the Indian Ocean.

I might add that a fresh Coho salmon presented to the club commodore, allowed "Nuthatch" to be declared winner of the race!

january

The good news however is that pinger detection distance is not an exact science and in fact is dependent upon so many variables that no one can say for sure at what distance that pinger will be detected at in any given moment. In  fact, a ping can be heard one moment and disappear the next (just as it has seemed to happen in this case). Slant range, thermoclines, pinger locator sensitivity, all come into play. The most important of these is the thermoclines. Favorable will result in the pinger being detected miles away. Negative will result in you not being able to detect it down the block, so to speak.

 

OK but most reference I see show the thermocline extending to 1000m, so if you tow below that you shouldn't be affected, right?  Is getting the detector that deep feasible?  At any rate, the attenuation of 37.5 kHz sound is going to be an issue, even if that sound energy gets into the surface layer.

 

scott s.

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OK but most reference I see show the thermocline extending to 1000m, so if you tow below that you shouldn't be affected, right?  Is getting the detector that deep feasible?  At any rate, the attenuation of 37.5 kHz sound is going to be an issue, even if that sound energy gets into the surface layer..

 

There are multiple thermoclines in most parts of the world's oceans at any given moment. That's why submarines can play hide and seek from each and still be less than 1,000 meters from each other at certain times of year, locations and depth. It is also why you could be sitting off the coast of Puerto Rico and detect a whale trumpeting off the coast of Ice Land. That's called "channeling". In the vertical however, the thermocline(s) are less opaque than they are when the sound wave is more angled to their boundary. So, given all the variables, it is possible that a locator towed at 500 feet could detect a pinger at much greater depth that the frequency of the emitter might lead you to conclude.

 

Yes, 37.5 KHz does not have the range that a lower frequency would provide. But, the driver in selection of that frequency was pinger transmitter / ceramic size and power consumption / space availability. Distance is inversely proportional to frequency. The higher the frequency, the shorter the absolute range (taking thermoclines out of the equation). So, it is a trade off between range, power consumption, ceramic size and available space. Having said that, a 500 KHz side scan sonar can work out to a 1,000 meter round trip path or greater depending upon the receiver's sensitivity. Also keep in mind that the BLUE FIN 21 (an autonomous underwater vehicle - AUV) is on scene and that renders all discussions of range, depth and sensitivities mute.

 

 

Yes, 37.5 KHz does not have the range that a lower frequency would provide. But, the driver in selection of that frequency was pinger transmitter / ceramic size and power consumption / space availability.

 

Another major reason is that there is very little else in the ocean that produces noise at this frequency. Choosing something that sounds like a whale or krill could be very confusing.

One major thing that I don't understand is how they could listen to a stationary pinger for 2 hours, from a moving platform, and not be able to get more than enough crossing bearings to zero in on it.  Am I to deduce that their towed pinger locator does not provide directional information?

One major thing that I don't understand is how they could listen to a stationary pinger for 2 hours, from a moving platform, and not be able to get more than enough crossing bearings to zero in on it.  Am I to deduce that their towed pinger locator does not provide directional information?

 

No, the receiving array in the locater is omni-directional. A towed long linear array, or a flank array would be able to give relative bearing, but the towed locater is simply a device to get you in the "neighborhood", so to speak. In order to provide bearing, you need either a three transducer array, such as an Ultra Short Baseline system that provides time differences between the arrival of the acoustic energy at each 'ducer face, or you need a long array with multiple receivers to give you arrival time differences, from which you can calculate approximate bearing.

Another major reason is that there is very little else in the ocean that produces noise at this frequency. Choosing something that sounds like a whale or krill could be very confusing.

 

When the first Dukane pingers were introduced, I am not sure we were smart enough to know that. I think the primary, and only, drivers at the time were size, power consumption and the expectation that the pingers would only be ever necessary in rather shallow water, rather than 15,000 feet. I can count maybe three incidents in deep water... Both Air India disasters and Air France in the mid-Atlantic. KAL007 and TWA800 both occurred in relatively shallow water where the debris fields were located almost instantly (relatively speaking).

That means a tow line of perhaps 20,000+ ft to get the hydrophone down to near bottom  where this search is occurring !! (The tow line forming a very long catenary arc behind the ship.)

No wonder the search seems so slow- the tow vessel having to turn on a very wide arc or else reel in the tow before turning.

Probably the latter to avoid the hydrophone sinking to the ocean floor during turn.

No wonder the process is slow. 

january                           

If I recall correctly, one report said it actually took 3 1/2 hours to make the turn each time...