I have to admit I love this one.
Apparently this is all in response to a couple incidents where the flotation would have had no value.
It is hardly a secret that the flight crew can close cabin and cockpit vents, allowing the plane to float more than long enough for an orderly evacuation to the life rafts. (I just googled it, so any ingenious inventor should have known). Of course, a controlled ditch into the ocean is vanishingly rare otherwise Capn' Sully wouldn't be an international hero. The normal airplane/water contact is either at high speed and the airplane shatters on impact OR the plane is destroyed mid air and the wreckage falls into the sea. Hard to see how flotation devices are helping here. Of course, flotation air bags occupy room even when decompressed and the tough material isn't exactly light; carrying enough of this stuff around to keep the plane afloat in when it isn't watertight for whatever reason is going to invoke a fuel penalty based on weight and another penalty because it will have to be carried external to the pressure cabin...increasing drag.
Then there is the question of how to store all this. Obviously we can't just carry bags on the outside of a plane like luggage on a minivans roof rack....most likely it would have to be under solid panels applied to the ships exterior. Now we have an interesting problem. A ditching 747 might make a landing just above stall doing say, 120 kts...about 135-140 mph for land lubbers. We need panels that can deploy rapidly and totally BUT they can't be ripped off going 140 mph on the water or the bags might suffer damage and the off center drag from the panel might cause the plane to yaw and flip. At the same time, the panel must be tough so that the impact won't derange the mechanism in some way that prevents deployment.
Yeah, I ain't even an engineer but a little analytical thinking shows just how wary you have to be of "ingenious inventors".
