What happened

On 23 November 2011, a loss of separation occurred 6 km north of Cairns, Queensland, between a Cessna Aircraft Company 402C (C402), registered VH-TFK, and a Cessna Aircraft Company T210N (C210), registered VH-PDP.

The C402 was conducting an instrument landing system (ILS) approach for runway 15 and was 1.8 NM (3.3 km) from the airport when the pilot initiated a missed approach from a height of 1,000 ft in instrument meteorological conditions. At the time the C210 was on the same ILS approach and was 6.4 NM (11.9 km) behind the C402. About 1 minute after the pilot of the C402 turned left to establish the aircraft on the missed approach track, the distance between the two aircraft reduced below the required air traffic control separation (ATC) standard.

What the ATSB found

The Australian Transport Safety Bureau identified that a local ATC procedure, published in part to assist ATC in separation management during a missed approach event, was not clear and subject to varying interpretation. This resulted in the spacing between the two aircraft being closer than intended at the point when the pilot of the C402 commenced the missed approach.

The local ATC procedure did not fully consider all operational aspects that may lead a pilot to initiate a missed approach in instrument meteorological conditions above the procedure-defined minimum cloud base height.

What has been done as a result

In response to this occurrence, Airservices has initiated a number of safety actions including amending the local procedure to assist with the clarity and intent, changing the Cairns local instructions to enforce minimum flow (distance) spacing and updating controller missed approach procedures refresher training. This updated training will increase controller awareness of separation assurance issues relating to consecutive approaches and ensure that due consideration is given by controllers to the broad mix of aircraft types using straight-in approaches.

Safety message

This occurrence reinforces the need for all local procedures, in particular those that assist controllers in separation management, to be unambiguous and to encompass all possible operational circumstances. The importance of effective radar navigation guidance when positioning an aircraft for an approach is also highlighted.