A federal report says a helicopter that crashed into the East River off New York City during a sightseeing tour last year was carrying too much weight.

The National Transportation Safety Board hasn't yet concluded what caused the crash.

Thursday's NTSB report says the Bell 206 chopper was carrying an estimated 3,228 pounds when it crashed shortly after takeoff in September 2011. The aircraft's capacity was 3,200 pounds.

The accident killed three people. The pilot and one passenger survived.

The NTSB report says pilot Paul Dudley told investigators he asked passengers' weights and calculated they wouldn't be too heavy. But the surviving passenger said Dudley didn't do so.

Dudley told the NTSB the chopper's nose swung unexpectedly to the left during takeoff and the aircraft then went out of control. His lawyer notes that the report says such experiences have been documented as a potential problem for pilots.