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On 25 May 2002, at 1157 hours Eastern Standard Time, a Cessna 172 (Cessna) came within approximately 600 m of a departing Boeing 747-300 (B747) while the B747 was climbing through the altitude of the Cessna. The pilot of the Cessna was tracking in accordance with what he believed to be the visual clearance issued by Cairns air traffic control at 1,000 ft AMSL. The B747 crew was tracking via a standard instrument departure (SID) which specified a left turn after take-off.

The aerodrome controller issued the pilot of the Cessna with a clearance to track via the 'southern shores'. The term 'southern shores' was referred to in the Cairns local air traffic control instructions as the 'southern shores of Trinity Inlet'. The aerodrome controller understood that the clearance referred to the shoreline between the Cairns inlet and False Cape along the southern shore of the Cairns harbour. The pilot of the Cessna was not familiar with the term 'southern shores' and thought the controller meant the shoreline on the southern side of Cairns airport (which was the northern shore of the Cairns harbour). The term 'southern shores' was not specified in any document available to the pilot.

The pilot correctly read back the clearance to the aerodrome controller. That correct readback indicated to the aerodrome controller that the pilot could comply with the clearance.

The Cairns local air traffic control instructions stated that a clearance to aircraft to track via the 'southern shores' was meant to provide wake turbulence separation between an aircraft departing Cairns via a runway 15 SID and an aircraft over the southern shore of the Cairns inlet.

The aerodrome controller reported that he had kept both the B747 and the Cessna in sight and that visual separation was maintained between the two aircraft throughout the occurrence. The ADC provided the Cessna pilot with turn instructions, to enable him to avoid the B747, and traffic information about the B747 and a wake turbulence advisory. The B747 crew received a resolution advisory from their traffic alert and collision avoidance system about the Cessna.

The controller issued a clearance to the pilot of the Cessna that was, to the aerodrome controller, a specified route but one that was not known to the pilot. The aerodrome controller was not aware that the pilot's understanding of the 'southern shores' differed from his own. The meaning of the term 'southern shores' was not available to the pilot of the Cessna and therefore the potential existed for the misunderstanding between the pilot and the aerodrome controller that resulted in this occurrence.

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