A small private plane collided with a sightseeing helicopter over the Hudson River on Saturday, scattering debris in the water and forcing thousands of people on the New Jersey waterfront to scamper for cover. Nine people on both aircraft were presumed dead, The Associated Press reported. A helicopter pilot refueling on the ground at the heliport for Liberty Tours, which operated the doomed sightseeing craft, saw the plane approaching the helicopter and tried to radio an alert to the pilots, police Commissioner Raymond Kelly said. The warning wasn't heard or didn't happen in time. «He radioed the accident helicopter and told him, 'One-lima-hotel, you have a fixed wing behind you,»' National Transportation Safety Board Chairman Deborah Hersman said Saturday. «There was no response.»