Union leaders said Monday that U.S. government safety officials made a mistake in a report that implied an air traffic controller could have prevented a mid-air collision over New York's Hudson River and demanded a retraction.

National Air Traffic Controllers Association officials said in a statement that the National Transportation Safety Board was wrong when it said that a controller at Teterboro Airport in New Jersey who was handling a small plane involved in the Aug. 8 accident failed to warn the single-engine Piper's pilot that there were other aircraft in his path, including the air tour helicopter. Minutes later the plane and helicopter collided, sending both aircraft plunging into the Hudson. Nine people died in the accident, including five Italian tourists.

Union officials said the NTSB's report later notes that the helicopter, which was just beginning to lift off, didn't appear on the Teterboro controller's radar screen until seven seconds after the controller handed off responsibility for the plane to nearby Newark Liberty International Airport and told the pilot to contact Newark.

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The report infers that the helicopter was among the aircraft visible on radar in the plane's path, which was not the case, the union said.

Union officials tried unsuccessfully over the weekend to persuade the safety board to change its report.

"We don't have any comment at this time," NTSB spokesman Peter Knudson said in response to the union.

The Teterboro controller made a personal phone call shortly after clearing the plane for takeoff at 11:48 a.m. EDT and remained on the phone until the collision five minutes later, even while he was directing traffic, according to the report and a Federal Aviation Administration statement.

The Piper pilot never contacted Newark, but just before the collision he acknowledged the Teterboro controller's instruction to change radio frequencies. The sequence of events raises the possibility the pilot's attention may have been focused on the radio so that he didn't see the helicopter.

After the helicopter appeared on radar screens, a Newark controller called the Teterboro controller to alert him to the possible collision, the NTSB report said. The Teterboro controller twice tried unsuccessfully to contact the pilot before the crash.

"The aircraft never made radio contact with Newark, as Teterboro had requested. Nobody was talking to him. You cannot issue traffic warnings to a pilot who is not communicating with you," said Ray Adams, NATCA facility representative at Newark, who is representing the Teterboro controller in the NTSB crash investigation.

The FAA said last week that it does not appear the controller could have prevented the accident.

The NTSB took apparent exception to that, stating in its report that it would decide what role the controller played in the accident and that other opinions at this time are speculative and premature.

The public spat between the board and the union and FAA is unusual. Typically, the union and FAA steer clear of any public statement regarding an ongoing investigation so as not to jeopardize their status as parties to the investigation. As parties to the investigation, they have access to information uncovered by the NTSB long before it becomes public.