Joy Garnett, who witnessed the accident, told Eyewitness News that the Bell 206 helicopter went down almost immediately after takeoff around 3:30 p.m.
Garnett said the helicopter was about 20 feet in the air, just yards away from the heliport at 34th Street, when it started to spin around and then crashed hard into the water.
"I thought, 'Is that some daredevil move?"' she said. "But it was obviously out of control. The body spun around at least two or three times, and then it went down."
The pilot and three others were pulled from the water shortly after it went down by rescue crews.
Scuba divers from NYPD and Fire Department located the helicopter under water and recovered the body of the fifth person, a woman. She was pronounced dead at the scene.
For an excruciatingly long 90 minutes, the fate of Sonia Marra Nicholson, in the murky East River, remained an unknown.
Then, there was confirmation that on her 40th birthday she was the lone fatality.
Among the survivors are her partner, 43-year-old Helen Tamaski, her mother, Harriet Nicholson, and her stepfather, 72-year-old Paul Nicholson.
Her parents are British but they live in Portugal.
Sonia Nicholson lived in Helen Tamaski's native Australia.
Paul Nicholson was sitting up front with the pilot, who was treated at the scene.
The pilot was identified as Paul Dudley, the airport manager at Linden Airport. According to officials, the helicopter, a blue and white Bell 206, is operated by Dudley and based at Linden Airport.
Dudley made an emergency landing near Coney Island in November 2006 while piloting a single-engine Cessna 172 plane. He was coming from Westhampton, N.Y. and going to Linden, N.J., when he reported engine trouble and landed safely.
The chopper, a Bell 206 Jet Ranger, is one of the world's most popular helicopter models and was first flown in January 1966. They are light and highly maneuverable, making them popular with television stations and air taxi companies. A new one costs between $700,000 and $1.2 million.
It was pulled out of the river and loaded onto a boat just after 7 p.m. on Tuesday. It will now be examined by the NTSB.
On Aug. 8, 2009 a small plane collided with a helicopter over the Hudson River, on the other side of Manhattan, killing nine people, including five Italian tourists. A government safety panel found that an air traffic controller who was on a personal phone call had contributed to the accident.
The Federal Aviation Administration changed its rules for aircraft flying over New York City's rivers after that collision. Pilots must call out their positions on the radio and obey a 161 mph speed limit. Before the changes, such radio calls were optional.
Earlier that year, an Airbus 320 airliner landed in the Hudson after hitting birds and losing both engines shortly after taking off from LaGuardia Airport. The flight, U.S. Airways Flight 1549, became known as the Miracle on the Hudson plane.
The river has been closed to commercial boating traffic, the U.S. Coast Guard said.
The weather was clear but a little windy Tuesday, with winds of 10 mph gusting to 20 mph and visibility of 10 miles, according to the weather station at LaGuardia airport. There were a few clouds at 3,500 feet above sea level, well above the typical flying altitude for helicopters.