The engines hit the water just after the body of the plane. The engines are designed to come off when they hit something.
When hit by something going 160MPH water is very hard and will knock the engines off the plane.
The birds ruined the rotors inside the engines so they stopped producing output. The water in the river tore the engines off the plane... just as it was supposed to do.
Howdy!
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This goes back to 1905..
Significant Bird and other Wildlife Strikes
The following is a selected list of wildlife strikes to civil and military aircraft.
http://www.birdstrike.org/commlink/signif.htm
It is amazing that some need a tutorial....