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

See-and-avoid conflicts
See-and-avoid conflicts where situational awareness errors were involved (also
contributed to by inadequate or no communications in some cases) made up about
one-seventh of all occurrences. These types of conflicts led to almost all of the six
accidents recorded in the vicinity of non-towered aerodromes between 2003 and
2008, four of which were mid-air collisions, and two of which were runway
incursions leading to a collision on the ground. Furthermore, there were 60 serious
incidents in which an accident almost occurred. Once again, these were mostly due to
a lack of communication between pilots or an insufficient awareness of nearby traffic,
leading to an airprox. In 87 occurrences, a Traffic Collision Avoidance System
(TCAS) alert occurred due to a potential separation issue. In over half of these cases
however, the TCAS alert was the only indication that pilots of an aircraft had of the
other traffic.
In approximately 20 per cent of all conflicts, one or more aircraft took avoiding action
to prevent a collision or an airprox. In a further 17 per cent, one aircraft made a
precautionary diversion from its intended flight path in order to maintain safe
separation with another aircraft that was not communicating or aware of other nearby
aircraft.
Inadequate communication between aircraft
Insufficient communication and broadcasts between aircraft, radio failures or
misunderstandings were the biggest contributors to occurrences in the vicinity of nontowered
aerodromes between 2003 and 2008 (388 of 709 occurrences).
Communication issues accounted for 38 per cent of all information errors and 31 per
cent of all action errors for these occurrences.
Good communication between pilots on the Common Traffic Advisory Frequency
(CTAF) is critical to creating a safe operating environment in uncontrolled airspace,
especially in higher traffic density locations such as at non-towered aerodromes.
Despite this, in almost a third of all occurrences, it was known (or likely) that the pilot
was operating within the vicinity (10 NM) of a non-towered aerodrome and not
monitoring the CTAF effectively. In 146 occurrences, the pilot did not have their
radio tuned to the correct CTAF at all.
Procedural errors and circuit operations
Procedural errors were the second most common occurrence group at non-towered
aerodromes (after communication issues). While not all of these occurrences
happened in circuit areas, the proximity of aircraft and workload of pilots in this
phase of flight reduces the margin of safety if procedural errors occur, or pilots do not
make the positional and intentional broadcasts on the CTAF as required by CAR 166.
In one-seventh of occurrences, an aircraft did not make a broadcast prior to taxi or
entering a runway, and in 28 occurrences, a pilot did not broadcast before entering the
circuit. Not making these broadcasts reduces the situational awareness of all other
pilots in the circuit, as they are not aware of what aircraft are in the air, where they
might be in the circuit, or if they are using or taxiing on an active runway.
Within the circuit, most incidences of reduced separation between aircraft were due to
at least one aircraft conducting circuits in a contrary direction to other circuiting
aircraft (i.e. aircraft coming head-on in the circuit), or aircraft on base leg conflicting
with those on final. This finding was supported by previous ATSB research into mid-
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