to Beausoleil -
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The airplanes I flew in my career - 707-727-747-DC8 - were all supposedly to float somewhat nose-up.
Your opinion about rear exits being unusable after ditching is correct.
Be aware that a few types are devoid of any "overwing exits".
And... 25 years ago, a certain "world favorite airline" suppressed their L3/R3 doors on 747s.
This to put an extra 12 or so seats... Superior thinking, with safety concerns.
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One rule applicable to any airplanes -
You only open a door after assessment of outside conditions (water/fire).
That is the reason why doors have a window...
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Happy contrails