4000+ meters.

So twice this depth would be very challenging for an aluminum tube....

"The pressure increases about one atmosphere for every 10 meters of water depth. At a depth of 5,000 meters the pressure will be approximately 500 atmospheres or 500 times greater than the pressure at sea level. That's a lot of pressure."

"Our" Prime Minister "Tony BlAAbbott" needs to pay better attention during his briefings :rolleyes:

From CNN.

The possible signal heard Thursday by airplane is unlikely to be related to Flight 370, the head of the Australian search effort said.
That signal would have been the fifth signal heard, after four were heard by a pinger locator towed by a search ship.

Separately, Australian Prime Minister Tony Abbott told reporters in China "we are very confident the signals are from the black box."

It was unclear if Abbott was referring to the four earlier signals, to the possible fifth signal or to all of the signals.

Lots of things become unclear when Tony speaks...

Sea plane or any tube (sub) going to that depth would just squash up like a tin can? When a ship sinks, does the ocean at that depth just crush what's left into oblivion?

Not necessarily crushed into oblivion, but yes, 'crush depth' or something siimilar how submariners refer to it. When I was in the Navy and flying S-3's (anti-sub), I remember our simulator had a recording of a sub being crushed after we would succesfully torpedo it in training. Several Tom Clancy novels have submarine sinkings in them where the shooters hear the sub being crushed on their acoustic gear.

Objects like broken wreckage would sink to the bottom relatively unaltered. It is not like it is being run over by a giant steam roller. Anywhere that water can seep into an airspace it will fill the inside and push out at the same pressure as the water pushing in. Things like spent oxygen bottles will be squashed flat if they were well sealed but a section of broken fuselage would remain intact. If the entire cabin of the aircraft remained air tight, it would probably float and not sink anyway. However, if it were somehow (very unlikely) dragged down under and remain completely sealed it would reach a depth where it would collapse catastrophically.

When I was working in deep sea seismic research, we would sink ocean-bottom seismometer units to the ocean floor where they would remain for a week or so recording data before detaching from their anchor and bobbing to the surface to be retrieved. The delicate electronics was enclosed in a crush resistant aluminum sphere. For fun we attached a Styrofoam coffee cup to one of the OBS before it was deployed. When it was retrieved, the cup was a miniature replica. The gas in each of the foam cells was compressed until it dissolved through the foam and into the water leaving behind only a tiny plastic blob for each of the cells, still attached to each other in their original shape. Only thing, the shape was reduced in size.

good point, anything that's compressible (like a submarine or a sytrofoam cup - that's pretty cool)will collapse...wreckage wouldn't. The Titanic still looks relatively intact, but broken, sitting way down there.

Great post, it's all about pressure differential. If the airplane filled with water and sank, there would be no pressure differential between the water outside and the water inside, so no crush. But if it somehow landed with the pressure vessel (cockpit/cabin) intact, then sank, eventually the water pressure would exceed the strength of the fuselage and crumple it, filling it with water and equalizing the pressure.

That assumes that the fuselage is airtight, which is incorrect. A number of the fuselage seals on a pressurized airplane are inflatable and bleed air driven, without the engines running they would leak down. Further, pressurized fuselages have an acceptable leak rate, none of them are 100% sealed. Even if you were able to gently land an airplane on the water (Hudson River), it would eventually fill with water and sink.

But...in any case, there is plenty of stuff that would float and given the amount of time, it is still interesting that not a single piece of floating debris has been identified. That is almost unexplainable at this point.

While I'm not sure how fast the ocean currents are down there, I have read that some reach 75 miles a day. So the plane went down roughly 30 days ago. 30 X 75 = 2250 miles. It's the start of the winter season down there and I'm sure that some storms have happened. Very light materials could get blown a lot further distance than that. So if the area of the debris was as long as it could be wide 2250 X 2250 miles that is a huge area to spot a 2' X 2' seat cushion floating in. There is also floating patches of debris in each ocean that traps more junk every day. The one in the Pacific ocean is reported to be the size of Texas.

When I saw the Titanic exhibit they had a styrofoam cup that they introduced to the same pressure as the depth the Titanic sank at. It was just like you described, a miniature version of the full size up, like the size of a thimble.

Zactly - that's the whole premise of theoretical super-deep dive suits where the diver could "breathe" an oxygen-carrying liquid (perfluorocarbon-based). The theory is that the liquid (incompressible) inside a suit (which the diver could also breathe) would help to equalize the pressure inside and outside, giving much better resistance to crushing. I've no idea where the research is on that - just that it's something that was being looked at about 15-20 years ago with implications for super-deep diving and high-G load suits. Crazy stuff.

The technology for this would work but you still have to problem of decompressing after a very deep dive. I'd imagine weeks in a chamber after such a dive.

I couldn't agree more. That's why I think the plane is not there at all. Meanwhile the search goes on. Hopefully at some point we'll all know what happened.

FDR tells you what happened.
CVR tells you why it happened.

But yeah, (as already stated by another poster) 2 hours of windnoise and automated alarms will be of limited use.

Started wondering about this and quickly came the conclusion that it's a non-starter. Problems that must have been considered were lungs and vocal chords REALLY don't like foreign fluids, how are air-filled cavities (sinuses...) going to be filled with fluids, how are all these fluids not going to become a giant medium for infection, how will anyone see without some gas filled space in front of the eyes....

While even the experts are puzzled by the lack of debris, there are a few reasons that can help explain the missing materials.

First, if the plane went into the water as most think, any debris field will be much more restricted in size than if the plane came apart in the air. Second, there was a force five typhoon within two days of the assumed crash, in the exact area where the pings are located. Any floating debris would have been widely scattered by that one event alone. Third, the area where the pings were located was not even searched until over three weeks had passed. Any debris floating after the crash would have had plenty of time to float far from the site and, possibly sink if it was susceptible to water absorption. Fourth, it's possible any debris was very small to begin with and floating with little exposure above the surface making it very difficult to see even if right on top of it. Fifth, the great unknown, it's possible that the plane went down relatively intact with very little debris left behind. Add that to the elements listed above, and the likelihood of finding it right away is very small. Finally, keep in mind this disappearance is unprecedented in its lack of information as to location. The crash it is most often compared with is AF477, and in that case, the general location of the crash was known, and a debris field was located.

I'm certainly no expert, but given the circumstances of this particular incident, I don't find it especially mysterious that no debris has been found yet, and I'm convinced some debris will eventually be identified, probably from some random discovery by an unofficial search entity.

If the aircraft ran out of fuel at say 25,000ft without pilot input would it have any glide slope or would it nose dive? I remember being amazed at the tiny impact zone on the WTC from an aircraft hitting at 500mph.

I have participated in in a number of search and rescue operations, all with a fairly narrow circular area of probability. Even then spotting a human in a raft in any sea state above 1 is difficult...small debris, the detritus of a plane wreck after three or four days?

I also did the test of the Downed Aviator Locator System (DALS) in the late '80's. The system basically used the PRC-90 radio we all carry in our survival vests as a beacon and allowed an aircraft equipped with DALS to "hone" in on the signal and fly on top. DALS was developed because of the fact that airborne search assets routinely flew right over survivors in the water and failed to spot them.

I flew hundreds of simulated rescues using DALS equipment.

We started with just having the guy sit in a large boat and emit...worked great.

We then put guys in survival rafts in the Chesapeake, MUCH harder to spot, even knowing where to look.

We then put the guy in the water with just his floatation gear...on certain heading, sun angles, etc., even knowing where to look, it was difficult, very difficult to spot the person.

That and very little in a jet liner that is visual floats for long...combined with an open ocean search without a define CEP and there is no mystery in the lack of debris, at least to me. Something will come ashore.

In a simple airplane, if power is lost, and there is no pilot input and the aircraft's autopilot has all three axes engaged, it will glide downwards at the same speed at which it is trimmed during powered flight. So if it was cruising under power, at say, 150 knots, then it will glide at the same speed. If the airplane is trimmed for a certain speed, and you add or reduce power, the airplane will climb or descend at the trimmed speed; it won't go faster or slower, unless the trim is reset.

But I don't know whether there are overrides in a Boeing 777's automated flight controls.