The National Transportation Safety Board report doesn't conclude what caused the crash; a determination was expected in about two months.
But the report said the Bell 206 chopper had a capacity of 3,200 pounds. The estimated weight at takeoff including all five passengers and fuel was 3,228 pounds, the report said. Federal investigators also weighed the helicopter after it was pulled from the river and estimated it could have been as heavy as 3,461 pounds, but that figure included soggy cushions and other water trapped in the aircraft after it was raised.
Pilot Paul Dudley reported that he asked people for their weights and calculated that they would not be too heavy, according to the NTSB report, but the surviving passenger said the pilot did not ask and didn't calculate the total weight.
A call to Dudley, the manager of the Linden, N.J. airport, was not immediately returned Thursday.
The helicopter sputtered and crashed shortly after takeoff from a riverbank heliport on Oct. 5, 2011. It sank 35 feet below the surface of the slow-moving water off 34th Street in midtown Manhattan, a few blocks south of the United Nations headquarters.
The sightseeing tour was part of a birthday celebration. The passengers were friends of the pilot's family: Paul and Harriet Nicholson, a British couple who live in Portugal; the wife's daughter, Sonia Marra, also British, and the daughter's partner, Helen Tamaki, a citizen of New Zealand. The daughter and her partner were living in Sydney.
Marra died at the scene, her body was pulled from the wreckage. Harriet Nicholson and Tamaki died later.
Paul Nicholson survived.
Dudley, 56, told the NTSB that the nose of the helicopter swung unexpectedly to the left as he was taking off. When he tried to turn right, the aircraft suddenly went out of control and hit the river. The type of problem he described to investigators, known as an unanticipated "yaw," has been documented by the Federal Aviation Administration as being a potential problem for pilots, the report said.
The surviving passenger told federal investigators that the chopper's nose was pointed down at takeoff and he was leaning forward in his seat against the restraint. "The helicopter then began moving 'erratically,' the pilot made an exclamation similar to 'oops' and the passenger then 'knew something wasn't quite right,'" according to the report.
The helicopter had been inspected two days before the crash and had no problems. An examination after it was pulled from the water showed no major engine malfunctions. A drug and alcohol test for Dudley came back negative.
Dudley was an experienced pilot with more than 2,287 hours of flight experience. On April 21, 2011, he failed part of his commercial pilot certificate test. He was re-examined on takeoff, landing and go-arounds three days later and passed, according to the report.