The FAA had no comment.
A second recommendation called on the FAA to emphasize the need to remain attentive to air traffic controllers. Questionable behavior during the incident led to the suspension of an air traffic controller and his supervisor at Teterboro Airport in northern New Jersey, where the plane originated.
"The NTSB is concerned with the complacency and inattention to duty evidenced by the actions of the (Teterboro) controller and supervisor," NTSB Chairman Debbie Hersman wrote, indicating that the male controller was joking with a female friend by phone when the collision occurred.
The controller's supervisor was running a personal errand and couldn't be found immediately after the accident.
Teterboro Airport has had more than its share of problems in recent years. Two men were injured in the fiery crash of a small plane there last week. A 2008 report by the Government Accountability Office found 23 runway incursions - incidents in which aircraft and vehicles stray into areas designated for takeoffs and landings - from fiscal 2001 through 2007. That was only two fewer than nearby Newark Liberty International Airport, which handles about three times as many flights.
Patrick Forrey, president of the National Air Traffic Controllers Association, defended the controller and accused the NTSB of rushing to assign blame.
"The bottom line here is that the controller is not responsible for contributing to this tragic accident and he did everything he could do," Forrey said.
Controllers typically focus on airliners operating in controlled air space, rather than the small helicopters and planes in the Hudson River air corridor. However, the plane's pilot had specifically requested to be followed. The NTSB letter indicates he was on a radio channel used by controllers when he was over the Hudson, instead of the channel local pilots use to tell one another where they are in the corridor between New York and New Jersey.
The letter notes that the controller's workload was light and should have enabled him to provide more information to the pilot about air traffic in the area.
Aviation experts welcomed the NTSB's proposed separation of slow-moving helicopters, which carry commuters and sightseers through the Hudson air corridor, from faster planes. The 1,100-foot-high corridor is not subject to the same flight plans and air control as the airspace above it, which is frequented by larger airliners.
Hubert "Skip" Smith, an associate professor emeritus of aerospace engineering at Penn State University, predicted early on that the midair collision would lead to the separation by altitude.
"It's important to separate helicopters and planes because they're so different and move at very different speeds," Smith said Thursday. "The helicopters are mostly engaged in local traffic, carrying sightseers and commuters, whereas the planes are mostly passing through."
Matt Zuccaro, president of the International Helicopter Trade Association, said the congested Hudson corridor is relatively safe and the midair collision is the first there in 26 years. However, he said he supports any recommendation that can make it safer.
Hersman wrote in the NTSB letter that established procedures aren't enough.
"Our recommendations," she said, "suggest operational changes that can make this corridor a safer place to fly."
Associated Press writer Joan Lowy in Washington contributed to this report.