Two of the victims remain in critical condition.
The loss of tail rotor effectiveness or LTE, can occur in low-speed flight, such as take offs and if not handled correctly by the pilot can send the helicopter into an uncontrollable spin.
The National Transportation Safety Board has been putting out safety recommendations about it since 1984. Helicopters most susceptible to LTE are bell 206b's, the exact model helicopter that crashed in the east river.
"When you lose tail rotor or the effectiveness of the tail rotor, you have controllability problems, specifically the helicopter will literally start to turn like a top," said Brian Alexander, Helicopter Pilot and Attorney.
That spinning is exactly what happened seconds before the crash. The pilot also faced a tailwind . The FAA advisory lists tailwind as a "condition under which LET may occur.
The advisory to pilots also points out 'Tthere is greater susceptibility for LTE in right turns".
The NTSB said the pilot had been 45 degrees into a right turn when he knew he had a problem.
Besides the wind and the tail rotor, weight and how it was distributed may also have been a factor.
If the aircraft had a full tank of fuel, the helicopter would have been pushing its maximum weight capacity.
"Leaving you with a mere 900 pounds approximately for your passengers and other equipment. So here, even if we use the FAA average of approximately 175-180 pounds, you're right up against that limit. adds Alexander.
More on the victims
The victims included a family from overseas, in New York City celebrating a birthday with a helicopter tour. The pilot was their friend.
It was the birthday girl who was killed in the crash. Her mother and her partner are listed in critical but stable condition.
The four passengers were friends with the pilot, Paul Dudley, who was planning to take them on a sight-seeing tour when the chopper crashed moments after taking off.
Dudley and three passengers made it to the surface of the water. But police divers found the body of Sonia Marra 90 minutes later, in the back seat of the submerged chopper. The group was in town to celebrate Marra's 40th birthday.
The surviving passengers are identified as Marra's mother, 60-year-old Harriet Nicholson; her stepfather, 71-year-old Paul Nicholson; and her partner 43-year-old Helen Tamaki.
The Nicholsons are British, but they live in Portugal.
Tamaki is from New Zealand and lives in Sydney, Australia, with Marra.
Dudley, 56, flies out of the airport in Linden, New Jersey, where he also manages the facility.
NewsCopter7 pilot Captain Randy Empey saw Dudley five minutes before he took off.
"He was excited," Empey said. "He was going to pick up his friends from the city, give them a little tour."
Dudley, an experienced pilot, has been in the news before. In 2006, he made an emergency landing in his Cessna in a park near Coney Island.
"We're trained to look for places to land," he said in an interview following that incident. "That's all there is to it."
He escaped injury in this crash and helped his three surviving passengers stay afloat until help arrived.
Paul Nicholson was treated and released from the hospital. He reportedly spend the night by his wife's bedside.
Marra previously owned two restaurants in Australia and has recently worked at a fruit market, where friends are remembering her jovial personality and spirit of adventure.
This is the seventh helicopter crash in either the Hudson or East River since 1995.