only possible cus he still had the rotors turning. otherwise the chopper would be at the bottom of the lake. also there was a lot of yellow tape on the chopper which indicates very important electronic items that can't get wet. that is the only way it was possilble.
These helicopters have a boat hull;therefore,they are designed to be buoyant - it is not just the rotors keeping him afloat. The yellow tape is to keep water out.
