Safety in the vicinity of non-towered aerodromes - Australian ...

7.3 Avoiding action taken and collision risk
In occurrences where a collision did not occur, the collision risk was still studied,
based on the information provided by the pilots/flight crews involved.
7.3.1 Avoiding action
For each of the 709 occurrences in the reporting period, an avoiding action rating was
coded based on summary information provided by the reporting pilot/flight crew. Not
all avoiding action involved two aircraft in the air – many occurrences involved
missed approaches and go-arounds of aircraft on final approach when seeing that the
active runway was occupied by a ground vehicle or a backtracking aircraft.
Avoiding action was not necessary in about 60 per cent of occurrences, either because
the aircraft was not in conflict with any other aircraft, or because conflicting aircraft
communicated with each other and changed their intentions to avoid reduced
separation (Figure 14).
In order of increasing collision risk, the avoiding action ratings assigned were:
• no action taken/no conflict
• one or both pilots/flight crews assessed the collision risk, determined the risk was
low, and continued on course/intentions
• one or both pilots/flight crews made a precautionary diversion from
course/intentions to reduce the risk of a separation issue or airprox from occurring
• evasive avoiding action taken where a collision was imminent.
Figure 14: Avoiding action taken in 709 non-towered aerodrome occurrences,
2003 to 2008
7.3.2 Collision risk
Apart from the four mid-air collisions described above, there were 55 airprox
occurrences at non-towered aerodromes between 2003 and 2008.
For each airprox occurrence, the ATSB makes a collision risk assessment based on
information provided by the reporters about aircraft proximity, relative tracks and
relative speed. In 51 of the 55 airprox occurrences, a collision risk assessment could
be made, as an estimate of aircraft proximity was reported.
- 60 -