Cessna Aircraft Company 172, VH-JER

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.