It depends on entry angle and the speed of the craft. If she did what I suspect, augured in, doing close to the speed of sound, it means she would have shredded as she plunged several dozen yards into the drink. The debris field would have eventually slowed to a stop a long way underwater, where some may have floated free, but most would have balled up in the wreckage and sank in a heep of twisted metal. Considering the time and predictable dispersion rates, before any reasonable contact could have been made, much of the little remaining debris would have scattered, making spotting it extremely difficult.
It's very unlikely she entered at a low angle and speed, mostly because of the glide slope characteristics of the aircraft, which will be in the 20' a second range, clean and dead, assuming the pilot is trying to fly her, much worse if not. There's also the APU problem on a dead stick, so pressurization would have been an issue. Obviously it will depend on the aircraft's condition of door seals etc, but there will be a significant DeltaP reduction once the engines stop.
If the aircraft was trying to ditch, she would have used a steeper decent and peeled off speed, by punching the gear and flaps at 2,500', using the excess speed to level and slow, for a controlled ditch. If this was the case, she would have broken up on the surface and a much higher level of debris prospects would have been available. Since nothing has been found, not even a seat back, it's very probable she augured in at 650 MPH, breaking up 100' or more below the surface, where little would float back up.
I have to disagree very respectfully. If the plane had lost power for any reason especially loss of fuel, the RAT (ram air turbine) would have popped out, and maintained all flight controls, autopilot, etc, for the duration of flight. The autopilot can, and does, fly the plane much better than almost any pilot. Actually, on the 777, a 'fly by wire' airplane, the autopilot DOES fly the plane all the time, the pilot is like a pilot on a ship? advice only. True cabin pressurization would have been lost, but it escapes through seals and the odd small door (which are never sealed, being small enough to be left to leak continuously).
Best case, the aircraft maintained ‘flight’ well, under full autopilot, mushing down in a semi stalled condition at about 160kts, and 15’ alpha.
Note; I've heard commentators saying someone would have had to turn the autopilot ON, not true, they would have had to turn it OFF, as its normal position, in flight, is ON. Remember, the 777 is fly/by/wire, has no connection between the pilot and controls, AND could not be controlled by a human even if they were connected physically.
In this case the tail would have hit first, then the body ‘belly flopped’ onto the surface. Whether the engines departed at this, (departure apparently depends on the exact wave face position when the plane hits it for this), i don't know, but i suspect not, no fuel slick. Having empty wing tanks, the plane would have floated intact, no debris at all for several hours. Eventually, water would have dribbled in through the various (pneumatic) baggage door seals (they lost their air pressure when the main engines stopped), and slowly filled the baggage compartment. As more water entered, the wings would eventually have been drawn below the surface, and at about 200psi, the rear spar webs would have failed, probably near the wing root, or wheel well. This is a design feature, and prevents bursting the wing fuel tanks by over-enthusiastic filling. Yes i know the tank pressure goes the opposite way, but the web fails in a controlled way both directions.
Now with the wing tanks and the body filling, still slowly, with water, there is a good chance the 777, still quite recognizable as an airplane, would ‘glide’ at about 8kts, and at about 20:1 glide angle. This means, in an ideal world, the plane will glide underwater about 20km for every 1,000m of depth it sinks. This is a long way.
Eventually, the body will fill with water, or the body will crush to the volume of the water that did get in. The same with the wings, but the wings have more opportunity for water to get in, especially through the rear spar webs, and the rib/stringer/skin combination is quite strong in the pure vertical, or Z direction. The wing may stay quite recognizable, and with reasonable aerodynamic shape, all the way down. Incidentally, the tailcone, empenage etc will flood immediately, whilst ailerons, rudders, elevators, and flaps would be crushed immediately (due to construction).
Under these conditions, NOTHING would escape, no hydraulic oil, no engine oil, and except for the fuel residue from the empty tanks, nothing to float. Nothing from the cabin, no luggage, no safety gear, no seat cushions, nothing.
Worst case, as described by you, would be loss of power followed by stall. With no RAT, no power, no electronics, the 777 is unstable, no human can control it anyway. It would start to fall like a leaf, then gradually point down until it reached (not exceeded) the speed of sound. Now all the flaps, the gear doors, and probably ailerons would be shed, and as it reached its buffet limit, at about the speed of sound, it would have lost the empenage, then the wings, torn bodily from the body leaving a hole about along the PAX floor line, and down to the ‘keel’ between the wheel wells. As this was coming off, the body would have tried to stop (slow down anyway) in mid air, its light and bulky, whilst heavy items, like landing gear, engines, the wings, and the complete contents of the cabin would keep going down. Much of this debris, ailerons, flaps, elevators, gear doors, would float, for weeks, if not months. Any safety equipment, including seat cushions, would also float, for years in this case.
Lets assume for a moment the plane actually “augured in’, a technical term not usually used in the aircraft industry. Had it descended in a series of stall/swoops, then its impact speed would have been 160kt and nearly flat, see above, or 350kt, and nose down. In this case, it could not enter the water at all, but it would be like hitting a concrete runway vertically. The plane would have concertinerd up until it reached the wing front spar, then spit circumferential. Little or no internal pressure influence at all. Regardless, the contents of the body, not to mention residue fuel and hydraulic oil would be spread all over, and much of this does float.
I think the total lack of debris is significant in this crash.
Mind you, a MD-80? went straight in to a Florida swamp, and was it never found? the swamp swallowed everything that time, leaving only a few disturbed plants.
