ELT, old or new, will not work underwater. Maybe a few feet...Maybe. Radio doesn't travel through water.

If it were floating on the water, it would work.

OK. What is SONAR then? The HC-130's Cook Tracker picked up re-entering space craft in the ionosphere, S-band signal sine waves and the ELT that was under the Sea of Ohkotsk. The radio frequency of an ELT is 121.5 and 243.0. The pinger is ultra low frequency and you may not hear it on your radio, but a P-3 or my HC-130N did. It was built to find objects under the water, of the highest national priority.

Someone posted this on another site: NOAA data for 4 days ago shows a major disturbance of three of the buoys west of Smith Island (in the Andaman Sea - also known as the Nicobar). Displacement of the first buoy shows approximately 1500 feet (down). Weather doesn't seem to have been severe enough to cause this type of disturbance.

According to Wikipedia, 571 feet. We saw the trawler bringing the submersibles for the Soviets, and they weren't the only ones down there.

SONAR is soundwaves...

The "pinger" is an acoustic device as well, not RF.

Even VLF only goes down to 20 meters below the surface. Submarines use that for communications when they would come up near the surface. Only ELF frequencies can penetrate down to submarine operating depths. VHF and UHF have far less penetration that is limited to just below the surface.

I don't think an ELT is useful for SAR if sunk underwater very deeply. 25 feet+ I doubt it. RE: radio waves

I would think a US military/intel agency has the ability to detect a large, odd, object in the ocean tho and am certain we will hear some news in a few days yeah/neah on located wreckage. SAR performed by Vietnam, no, US agencies, yes

If I am not mistaken,the ELT and the FDR both communicate through VHF and UHF frequency, and a VLF pinger, and we picked up the pinger in the vicinity of on Northern Hokkaido enroute to the AO. You are correct about the sound waves of SONAR. That is why we had a Radio Operator on the HC-130 and knuckle dragging pilots to fly the airplane. He got the DF steer off the tracker, and I thought it was only possible with VHF, UHF, S-Band and HF. The pinger indicated location through receiver intensity. Somehow we were accurate enough for 2 SU-15's and three Mig 23's to launch on us. This was also the only mission I ever flew where the PJ's did not want to jump.

Sorry, I edited my post as I was discovering more information:

ELTs are radio only, no sonar. Modern ones use EHF, older ones VHF. As was mentioned only ELF radio can penetrate any depth of water and that requires an antenna array larger than almost any other structure on earth. The US navy used to use that to communicate with subs. Maybe you had that?

FDR and/or CVR have a sonar pinger activated by exposure to water. That sound would be detectable only by military sonar receivers or specialized civilian gear. It would not be detectable by a radio receiver, I don't think FDR/CVR even have radio beacons...assumption being if the wreckage is on land the ELT would provide the beacon.

Not sure how you located KAL unless the ELT was floating or very, very shallow. Aircraft can easily use sonobouys to detect/locate underwater sound sources, but it requires special onboard receiving gear normally found on navy aircraft.

No, not useful.

No they don't. If you can solve that problem the patent will be worth hundreds of millions and will put every submarine in the world out of business. Two-billion-dollar subs are only useful because they CAN'T be found easily.

To find anything on the bottom will require military or specialized civilian vessels with sonar gear to search the ocean floor one meter at a time. Not practical until you narrow down the search area.

I can think of one potential means by which the crash location could have been detected but I would have thought they would have announced that by now if that was the case.