The alertness and quick thinking of a pilot over the Atlantic averted a mid-air collision with another passenger aircraft over the Atlantic, a report by the Air Accident Investigations Unit has found.
A breakdown in communications during a critical eight-minute period when the disappearance of a Swissair MD-11 aircraft from a radar screen was not noticed was "an extraordinary lapse of concentration" by the radar controller and the planning controller in Shannon, the investigators stated.
During that period, a second eastbound aircraft in the area, an American Airlines Boeing 767, was instructed by Shannon Radar to climb into the assigned level of the Swissair aircraft and passed just over half a mile from its left wing.
The two aircraft are understood to have a passenger capacity of about 500 people.
The controllers were subsequently relieved of their duties following the incident in July 2000, while a management inquiry was carried out by the Irish Aviation Authority.
A spokeswoman said yesterday that relieving controllers of their duty was a standard practice and they were now back on duty. They had not been sanctioned for their concentration lapse. She said sanctions could lead to non-reporting of such incidents, which could compromise safety in the industry.
The aviation authority had accepted the investigation unit's recommendations that an urgent examination be carried out into the failure of the radar system. This was described as a contributory factor to the near miss of Swissair flight SWR 127 from Boston to Zurich and American Airlines flight AAL 176 from New York to Frankfurt on July 3rd, 2000.
The unit also recommended that training procedures and practices employed by radar and planning controllers be "urgently" reviewed. The investigators praised the "situational awareness" of the commander of the Swissair jet, SWR 127, who, on his own initiative, took avoiding action to prevent a collision between his aircraft and the US aircraft.
The Swissair commander veered to the right when he noticed the American Airlines aircraft to his left beginning to climb. "The primary cause of this serious incident was the loss of SWR 127 radar signal due to a functional anomaly in the software, which led the radar controller to incorrectly give climb clearance to AAL 176," the investigators concluded.
The Swissair aircraft's short- term conflict alert system had failed to activate because of the earlier loss of the Swissair aircraft's radar track. Just before the Swissair commander took avoiding action, he received three warnings from his on-board radar system, the "airborne collision avoidance system".
It emerged that the other aircraft's avoidance system was not operating.
Following the incident, American Airlines reduced its minimum days for having an avoidance system inoperable from 10 flight days to three flight days.
"The investigation was unable to verify the exact passing distance between the two aircraft but said it had no reason to doubt the Swissair captain's assessment of the distance, the report stated.
The full report can be found at: www.irlgov.ie/tec/aaiu/
AAIU pages /aaiureportindex.htm