An air traffic controller should have warned the pilot of a small plane about aircraft in its path before it collided with a sightseeing helicopter carrying Italian tourists over New York's Hudson River in a crash that claimed nine lives, federal officials said.

The National Transportation Safety Board recommended that helicopters and small planes be separated in the busy air corridor where the collision occurred, a low-altitude pathway used by about 200 helicopters and small planes daily.

The call for fast-moving planes to operate at a higher altitude than helicopters is one of five safety recommendations the NTSB issued Thursday in a letter to the Federal Aviation Administration.

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A second recommendation called on the FAA to emphasize the need for air traffic controllers to remain attentive, a clear rebuke to the controller responsible for the single-engine Piper that hit the helicopter Aug. 8.

Questionable behavior during the incident led to the suspension of the 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 controller and supervisor," NTSB Chairman Debbie Hersman wrote.

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 afterward.

The NTSB's other recommendations deal with the procedures pilots and controllers should follow before an aircraft enters the corridor and once it's inside. They also propose training for pilots who wish to use the area.

The FAA, which doesn't have to act on the NTSB's recommendations, had no comment Thursday, agency spokeswoman Laura Brown said.

Teterboro Airport has had more than its share of problems in recent years. Two men were injured in the crash of a small plane there last week.

A 2008 report by the Government Accountability Office found almost as many runway incursions — incidents in which aircraft and vehicles stray into areas designated for takeoffs and landings — there as at nearby Newark Liberty International Airport, which handles 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 corridor. However, the Piper pilot was heading through the corridor to controlled airspace and had requested to be followed by air traffic control.

The NTSB letter indicates the pilot 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 said the controller's workload was light and should have enabled him to provide more information to the pilot about air traffic in the area. It said the helicopter was not visible on radar when the controller was in contact with the plane's pilot but there were other aircraft in the area that could have been brought to his attention and were not.

The collision between the Piper and the Eurocopter helicopter showered debris on the river and the streets of the northern New Jersey community of Hoboken. Five Italian tourists aboard the helicopter and their New Zealand-born pilot were killed, as were two men and a boy from a Pennsylvania family on the plane.