(CNN) -- A personal phone conversation by an air traffic controller likely contributed to the cause of a deadly midair collision over the Hudson River last year, the The National Transportation Safety Board said.
A single-engine plane and a sightseeing helicopter collided on August 8, 2009 near Hoboken, New Jersey. All nine people aboard the two aircraft were killed, including several Italian tourists visiting New York from Bologna.
In a statement released Tuesday, the NTSB said the air traffic controller's personal phone call "distracted him from his air traffic control duties, including the timely transfer of communications for the accident airplane to the Newark Liberty International Airport (EWR) tower and correcting the airplane pilot's incorrect read-back of the EWR tower frequency."
The on-duty personal phone conversation might not have been the first for the air traffic controller.
An NTSB report says the controller's personal call might not have taken place "if the front line manager had corrected the controller's performance deficiency involving an earlier nonpertinent telephone conversation."
In addition, the board said, the "front line manager, who was not present in the air traffic control tower at the time of the accident, exercised poor judgment by not letting staff know how he could be reached while he was away from the tower and by not using an available staffing asset to provide an additional layer of oversight at the tower during his absence."
The NTSB said another probable cause was the limitations of the "see-and-avoid" concept.
"The see-and-avoid technique of averting mid-air collisions was not effective because of the difficulty the airplane pilot had in seeing the helicopter until the final seconds before the collision," the NTSB said.
The safety board said contributing factors included both pilots ineffective use of their aircrafts' electronic advisory system to maintain awareness of other air traffic; inadequate procedures of the Federal Aviation Administration for transferring communication among air traffic facilities near the Hudson River; and FAA regulations that did not provide for adequate vertical separation of aircraft operating over the Hudson River.
"The helicopter's climb above 1,000 feet was not consistent with company procedures and decreased the vertical separation between the aircraft," the statement said.
NTSB Chairman Deborah A.P. Hersman said the collision could have been prevented.
"While traffic alerts go a long way in helping pilots "see and avoid" other aircraft, these technologies are not, in and of themselves, enough to keep us safe," Hersman said in the statement. "Strong operating procedures, professionalism, and commitment to the task at hand -- these are all essential to safety."
The NTSB said it made recommendations to the FAA about changes in a "special flight rules area" surrounding the Hudson River corridor near New Jersey and New York. Suggestions include revising federal regulations to specify altitudes for aircraft conducting local operations.