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

EXECUTIVE SUMMARY
The Australian Transport Safety Bureau (ATSB) proactively monitors aviation
safety through the analysis of accident and incident data, collectively termed
occurrence data, to determine whether important trends are emerging. In recent
years, the ATSB has received an increasing number of occurrence reports from
pilots regarding operations at non-towered aerodromes. This extends to the
associated use of the radio frequencies allocated for communication between pilots
using non-towered aerodromes to establish situational awareness and separation
(Common Traffic Advisory Frequencies (CTAF), and formerly CTAF(R) (prior to 3
June 2010) and Mandatory Broadcast Zones (MBZs) (prior to 24 November 2005)).
Non-towered aerodromes are those where a continuous air traffic control presence
does not exist, or is temporarily not available (such as outside of air traffic control
(ATC) or control tower operating hours). Aircraft are specifically considered to be
in the vicinity of a non-towered aerodrome if they are in uncontrolled airspace,
within a horizontal distance of 10 NM (18.5 km) from the aerodrome, and at a
height which could conflict with operations at a non-towered aerodrome.
The purpose of this study was to review occurrences in the vicinity of all nontowered
aerodromes in Australia in order to explore the types of safety events that
occur, and the concerns raised by some pilots and industry stakeholders regarding
operations at non-towered aerodromes. The focus was particularly on occurrences
related to airspace use, procedures, and operations.
A total of 709 such occurrences were reported to the ATSB between 1 January 2003
and 31 December 2008. This period was chosen for analysis in order to look at
occurrences prior to and after the procedural and airspace changes introduced by
NAS 2C on 24 November 2005 at all non-towered aerodromes in Australia.
The bulk of the 709 occurrences illustrate the need for good communication and
both awareness of, and adherence to procedures when operating in the vicinity of
non-towered aerodromes.
Occurrence types in the vicinity of non-towered aerodromes
The most common airspace use and operational-related occurrence types at nontowered
aerodromes were related to communication breakdowns or insufficient
communication between pilots. Many of these led to reduced situational awareness
of the pilot, and reduced separation between aircraft or conflicts. Conflicts are
situations where the actions of an aircraft or ground vehicle interfered with the
flight of another aircraft. Conflicts do not necessarily result in reduced separation.
Non-compliance with published information, notices to airmen (NOTAMs) and
procedures also occurred frequently (approximately 20 per cent of occurrences).
Types of errors contributing to non-towered aerodrome occurrences
An analysis of the errors that contributed to all occurrences showed that both
procedural errors (action and decision-related) and communication errors
(information and action-related) were most prevalent (about 30 per cent of cases for
each), followed by situational awareness and position/proximity errors (separationrelated).
All these occurrence types contributed to the 501 conflicts recorded at nontowered
aerodromes between aircraft or aircraft and ground vehicles.
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