The crew of a Fairchild Industries Ltd. SA227 Metroliner were inbound to Williamtown, NSW, when the control zone and restricted airspace were not active. The copilot made an inbound broadcast on the common traffic advisory frequency (CTAF) at 20 NM south, to which no response was heard. The crew reported that at 10 NM south of Williamtown, as they were descending through 3,000 ft, they passed within an estimated 30 m of a low-wing, retractable landing gear, single-engine aircraft travelling in the opposite direction. The pilot in command, who was the pilot flying, reported that his attempt to avoid the other aircraft would not have been timely enough to affect separation and there was an Airprox.
The investigation was unable to identify the other aircraft and determine why its pilot had not used the radio to provide positional information when operating in the vicinity of an airport for which the use of a radio was required and to determine if the aircraft transponder equipment (if equipped) was serviceable.
The investigation found that since November 2005, the provision of radar services in the Williamtown area had been reduced when the military airspace was not active. That was due to an unresolved technical problem with the military secondary surveillance radar at Williamtown, which impacted the civilian air traffic control system. A replay of the military radar data showed that the Metroliner's radar return merged with the primary return (no identification or altitude information) of another aircraft travelling in the opposite direction, overhead Newcastle.
The occurrence demonstrated the limitations of the see-and-avoid concept as an adequate means of achieving safe separation from other traffic in an unalerted traffic environment. It also demonstrated the arbitrary hand played by good fortune in avoiding a mid-air collision over a populous area, when just one pilot in an airspace system that relies on the cooperation of all pilots, either cannot or does not choose to participate.