National Transportation Safety Board (NTSB) investigators have modified their preliminary report on the Aug. 8 midair collision of a small fixed-wing aircraft and a sightseeing helicopter over the Hudson River. They now say the air tour helicopter struck by the plane wasn't initially visible on radar to an air traffic controller handling the plane.

The Safety Board had previously said the controller failed to warn the plane's pilot of the potential for a collision with several aircraft in its flight path, including the sightseeing helicopter, before handing off responsibility for the plane to other controllers. The NTSB now says the controller at Teterboro Airport did not have the tour helicopter on his radar screen until seven seconds after he handed off the aircraft to controllers at Newark Liberty International.

The Piper Saratoga and the sightseeing helicopter carrying a pilot and five Italian tourists collided over the river, killing all nine people aboard both aircraft. The single- engine fixed wing PA-32R-300 (N71MC) ran into the rear of the Liberty Helicopter Tours Eurocopter AS 350 BA (N401LH) as the two aircraft were flying in the same direction.

The fatal accident took place in a narrow corridor of airspace over the river reserved for aircraft operating under "see and avoid" rules. The Piper Saratoga, which had taken off from the Teterboro Airport (TEB) was heading south over the river to Ocean City (NJ) Municipal Airport (26N). The helicopter, had just taken off from the West 30^th Street Heliport (JRA) on the West Side of Manhattan for a 12-minute sightseeing tour.

Helicopter pilots and others who frequently fly the Hudson sightseeing route, which keeps them under 1,000 feet in altitude, rely on special operating procedures, including broadcasting on and monitoring of a dedicated radio frequency designed to make pilots aware of nearby traffic. Such transmissions are recommended but aren't required.

In the aftermath of the fatal crash, the FAA on Aug. 13 suspended two air traffic controllers at Teterboro Airport who were on duty when the Piper collided with the helicopter over the river.

One of the two unidentified employees was the air traffic controller who handled the Saratoga flight but was on the phone "involved in apparently inappropriate conversations" at the time of the accident, the FAA said in a statement. The second was the traffic controller's supervisor, who was supposed to be present, but was out of the building at the time, the agency.

FAA officials said, however, that they do not believe the employees' conduct had any role in the collision. "While we have no reason to believe at this time that these actions contributed to the accident," the FAA said, "this kind of conduct is unacceptable, and we have placed the employees on administrative leave with pay and have begun disciplinary proceedings."

The National Air Traffic Controllers Association (NATCA), which represents the controller, said the Safety Board's initial report unfairly implied that the Teterboro controller could have prevented the collision.

"We believe the NTSB was wrong to infer there was a traffic advisory that could have been issued from Teterboro Tower to the aircraft," said Ray Adams, NATCA Facility Representative at Newark Tower, who is representing the Teterboro Tower controller in the NTSB crash investigation.

"The helicopter was not depicted on the radar prior to the switch of control from Teterboro to Newark Tower. Teterboro had no opportunity to call that traffic. The service of air traffic control is based on 'known and observed' traffic. The Teterboro controller had neither seen nor known about the accident helicopter at the transfer of communication to Newark.

"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. You have to reach the pilot first and the Teterboro controller tried twice, to no avail," Adams insists.

Added NATCA President Patrick Forrey: "Our air traffic controller at Teterboro did his job. We believe he is not responsible for contributing to this tragic accident and there is nothing he could have done to prevent it from happening. We respect the NTSB and we value our participation in NTSB investigations. But in this case, the NTSB has completely ignored our input, painted an unrealistic view of the job description of a Teterboro controller and fueled a public feeding frenzy that unfairly blames this particular Teterboro controller for not acting to stop the sequence of events that led to the crash.

"We respectfully ask that the NTSB immediately act to stop this rush to judgment that this controller had anything to do with the crash until the Board's full investigation is complete," the union boss stated.

Meanwhile, the NTSB removed the controllers union as a party to its fatal accident investigation.

Organizations and agencies are invited to participate in NTSB crash probes if they can provide technical expertise. At the outset of an accident investigation, the organizations sign an agreement to abide by NTSB rules. One states that parties will not reveal investigative information being learned through that process, nor publicly comment on it. Parties agree that only the NTSB will release factual information on the progress of the investigation and discuss the progress of the investigation with the public, including the news media.

But NATCA held a series of media conference related to the crash probe, and Patrick Forrey was informed that union representatives had been removed from investigating team.

"Although we appreciate the technical expertise our parties provide during the course of an investigation," NTSB Chairman Debbie Hersman said, "it is counterproductive when an organization breaches the party agreement and publicly interprets or comments on factual information generated by that investigation. Our rules are set up precisely to avoid the prospect of each party offering their slant on the information. I regret that we have had to remove NATCA from the investigation."