The pilot of a Cessna 150 (C150) was taxiing for departure from runway 33 at Cairns for a private local area flight. At 1610:15 Eastern Standard Time, he reported to air traffic control that he was ready to depart and was at the "Yankee" taxiway holding point. The "Yankee" holding point was located 837m north of the runway 33 threshold. The controller responded by authorising the pilot to "line-up" behind a landing Twin Otter aircraft. The pilot acknowledged and complied with that instruction.
The crew (a student and instructor) of a Beech Super King Air (B200), had been operating in the local area on a training flight. They had flight planned for a "touch and go" landing on their return to Cairns, with circuit work to follow. The student was the handling pilot and, at 1614:00, was cleared for a "touch and go" landing. The touch down point was expected to be at, or near, the instrument touch down markers; approximately 450m from the runway 33 threshold.
On hearing the crew acknowledge the landing instruction, the pilot of the C150 broadcast to the controller that he was still on the runway. At 1614:13, the controller instructed the crew of the B200 to "go round". The crew commenced the go-around from a position approximately 100ft above the runway and 200m past the runway threshold.
The flight progress strips for both aircraft were in the "active" bay of the aerodrome controller's console but the exact location within that bay could not be established. The controller remembered that he placed the landing strip for the B200 in the "runway occupied" position within the active bay when he issued the landing clearance.
The controller had forgotten that the C150 was lined-up and, although completing a visual scan of the runway before issuing the crew of the B200 with a landing clearance, did not see the aircraft at the "Yankee" intersection.
Other controllers in the tower were attending to their own duties at the time and were not aware of the impending incident.
The instructor in the B200 had seen the C150 on the runway and was expecting air traffic control to issue either a take-off clearance for that aircraft or a go-around instruction for his aircraft. As they approached the runway threshold, he briefed the student to expect a go-around and that if the controller did not issue an instruction, they would initiate a turn over the water clear of the departure path. However, the intended action was not initiated and the go-around was delayed until after the controller had issued his instruction.
The controller normally used the "runway occupied" position at the console. That position was used as a memory jogger to ensure that if the runway was occupied, a second user could not be cleared to use that runway. In this occurrence, had the flight strip for the C150 been placed in the "runway occupied" position, the controller should not have authorised the B200 to use the runway without first placing the flight strip for that aircraft into that same position; thus, a memory jog would have occurred, prompting the controller that the runway was occupied.