Tamaki was victim Sonia Marra's partner. They lived in Australia together and were visiting in New York with her parents for Marra's 40th birthday.
No details about the types of injuries she suffered in the crash are being released.
Marra's mother remains in critical condition. Her step-father and the helicopter's pilot suffered only minor injuries.
Mechanics had just wrapped up their annual inspection of the Bell 206 helicopter on Oct. 2, the National Transportation Safety Board said in the preliminary report released on Wednesday.
During an annual inspection mechanics take much of an aircraft apart and put it together again. The work can take several weeks.
Pilot Paul Dudley told the NTSB he had just taken off from the East 34th Street Heliport and was 30 to 50 feet above the river when the nose of the helicopter swung unexpectedly to the left.
When he tried to turn right to return to the heliport, the aircraft went out of control, Dudley told investigators.
Three-fourths of one main rotor blade broke off when the helicopter hit the water, the report said.
Investigators had previously said they were unsure if the blade broke before or after the impact. They have not found the missing piece, according to the report.
The helicopter was built in 1976 and had flown 11,580 hours, the report said. It had a 400-horsepower Rolls-Royce engine.
(The Associated Press contributed to this report)