(CNN) -- Federal officials Monday clarified their description of what an air traffic controller at New Jersey's Teterboro Airport could have seen on radar just before a tour helicopter collided with a small plane over the Hudson River.
The wreckage of a plane that collided with a helicopter is lifted last week from the Hudson River.
"The accident helicopter was not visible on the Teterboro controller's radar scope at 11:52:20; it did appear on radar seven seconds later -- at approximately 400 feet," the National Transportation Safety Board said in a written statement, referring to the timeframe of the collision, which happened shortly before noon on August 8.
By then, the Teterboro controller had switched control of the plane to the Newark airport tower, which the pilot never contacted, the NTSB said.
On Friday, the safety board had said in a report that the Teterboro controller did not advise the pilot of potential traffic when he handed off radar monitoring of the plane to the tower at Newark airport at 11:52:20 a.m.
The safety board said Friday: "At 11:52:20 the Teterboro controller instructed the pilot to contact Newark on a frequency of 127.85; the airplane reached the Hudson River just north of Hoboken about 40 seconds later.
"At that time there were several aircraft detected by radar in the area immediately ahead of the airplane, including the accident helicopter, all of which were potential traffic conflicts for the airplane."
What the statement meant was that the potential conflicts were visible at 11:52:20 plus 40 seconds, or 11:53:00 -- after control had switched to Newark, a spokesman for the controllers' union said.
National Air Traffic Controllers Association spokesman Doug Church on Monday applauded the deletion of the phrase "including the accident helicopter," noting that many who read Friday's release had interpreted it to mean that the controller could have alerted the pilot to the potential crash. "It's an important clarification," said Church in a telephone interview.
The aircraft collided at 11:53:14 a.m. All six people aboard the helicopter and all three people aboard the plane were killed.
In the same statement Monday, the NTSB accused the union of reneging on its promise not to reveal or comment publicly on investigative information learned during that process and removed the union from the collision investigation.
The NTSB cited NATCA news conferences held Friday and Monday as evidence of the group's failure to stick to its agreement and reiterated that it has not yet determined what role air traffic control might have played in the accident. NATCA officials on Friday told the news media that the helicopter was not visible on radar scopes until after the Teterboro controller handed off the plane's monitoring to Newark.
"It is counterproductive when an organization breaches the party agreement and publicly interprets or comments on factual information generated by that investigation," Chairman Deborah A.P. Hersman said. "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."
Church called his union's removal from the investigation "a face-saving move" by the NTSB.
The Teterboro controller began a non-business telephone conversation at 11:50:31 and ended it one second before the crash, according to the NTSB.