Surveillance service was reduced when two aircraft passed within 30m of each other
A Fairchild Metro came within 30m (100ft) of an unidentified single-engined aircraft on approach to Williamtown, New South Wales, during a time when the military secondary surveillance radar (SSR), which provides surveillance in the area, was suffering a technical problem, according to the Australian Transport Safety Bureau (ATSB).
The Metro, with 14 passengers and two crew on board, was on a scheduled service between Sydney and Williamtown on 19 August. Some 10nm (19km) south of Williamtown, as the Metro was descending through 3,000ft, it passed within 30m of a low-wing, retractable landing gear, single-engined aircraft travelling in the opposite direction. The aircraft has never been identified, says the ATSB.
At the time, the Metro was in uncontrolled Class G airspace. Surveillance service around Williamtown is provided by the military's SSR, but service was reduced when military airspace was not active. The ATSB says this was due to an unresolved technical problem with the military's SSR whereby a high level of short-term conflict alerts were being displayed to controllers.
As a result, at the time of the incident, the Williamtown radar was not connected to the civilian air traffic control system, the Australian Advanced Air Traffic System (TAAATS). In addition, there was no active Mode C signal from the unidentified aircraft.
The military radar data at the time of the incident showed that the Metro's radar return merged with the primary return of the unidentified aircraft travelling in the opposite direction above Newcastle.
Since the incident, the Williamtown Australian Defence Air Traffic System radar data has been incorporated into TAAATS after an antenna fault was identified and repaired.
Source: Flight International
