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Airspace design for strategic separation

Issue number: AO-2008-059-SI-01
Who it affects: Pilots flying in D airspace at a capital city general aviation airport
Issue owner: Airservices Australia
Operation affected: Aviation: Airspace management
Background: Investigation Report AO-2008-059
Date: 31 May 2011

Safety issue description

Moorabbin GAAP airspace design did not assure lateral or vertical strategic separation between traffic flows. This increased the risk of a mid-air collision.

Proactive Action

Action organisation: Civil Aviation Safety Authority
Action number: AO-2008-059-NSA-095
Date: 31 May 2011
Action status: Closed

A review of the utility of General Aviation Aerodrome Procedures airspace across Australia was carried out by an independent contractor on behalf of CASA. Following stakeholder feedback, a report was released on 15 December 2009.

The contractor’s report produced 24 recommendations covering a wide range of potential safety enhancements, including the following:

  • the establishment of strategic expert oversight for all Australian GAAP operations;
  • future strategic safety enhancements, specific safety enhancements;
  • planning to monitor changes to future airport activity that may affect safety, and methods for implementing change if it is deemed necessary;
  • the acquittal of relevant ATSB recommendations issued in 2004; and
  • limits on aircraft numbers operating GAAP circuit patterns.

On 15 July 2009, CASA issued a direction that had effect from 21 July 2009. The direction required that the number of aircraft in the circuit for one runway be limited to six, but allowing for one more aircraft to operate in the circuit with the intent of departing. The direction required all aircraft to obtain an Air Traffic Control clearance to enter, taxi along or cross any runway.

On 24 December 2009, the direction was amended so that the limiting number of aircraft would be increased to eight from 18 January 2010. That limit was to remain in force until Class D procedures were implemented at previously GAAP airspace aerodromes on 3 June 2010. On 3 June 2010, Class D procedures were implemented at all aerodromes where GAAP procedures had previously been implemented.

On 21 April 2011, the ATSB sought an update from CASA of its actions in response to the recommendations of the above report.

In response, on 9 May 2011, CASA provided the following update:

I refer to your email dated 21 April 2011 seeking a Civil Aviation Safety Authority (CASA) update on any completed/planned actions in relation to recommendations from The Utility of General Aviation Aerodrome Procedures (GAAP) to Australian-administered Airspace Review Report (Version 2 – 15 December 2009).

The GAAP to Class D project involved an extensive national pilot education program focussed primarily upon operations at the then GAAP aerodromes. The program was widely acknowledged by industry as one of the most comprehensive and effective education processes ever undertaken by CASA. The transition at these locations has provided the following safety enhancements:

  • increased alignment with international practice together with greater standardisation of procedures nationally;
  • increased Air Traffic Control Tower staffing through the requirement to establish a permanent Surface Movement Control position, thus both providing increased capacity to monitor airborne traffic and enhancing ground movement safety;
  • an ongoing program to remove compulsory Control Zone entry points providing additional flexibility for traffic management; and
  • reduction in airborne radio congestion through the extended use of abbreviated clearances. A Post Implementation Review has been undertaken to examine the outcome of the changes and is expected to be completed by mid 2011.

ATSB response:

The ATSB is satisfied that the action implemented by the Civil Aviation Safety Authority, in conjunction with the action implemented by Airservices Australia (see the following section) will adequately address the safety issue.

Proactive Action

Action organisation: Airservices Australia
Action number: AO-2008-059-NSA-123
Date: 31 May 2011
Action status: Closed

In response to this safety issue, on 31 March 2011, Airservices Australia (Airservices) advised that:

Airservices Australia thanks you for the opportunity to provide additional feedback in respect of the Safety Actions identified in draft report, as requested during our meeting on 21 March 2011.

As stated in Airservices' initial response, we consider that there is insufficient weight of evidence or depth of analysis in the report to conclude, 'The Moorabbin Aerodrome General Aviation Aerodrome Procedures [GAAP] airspace design did not assure lateral or vertical strategic separation between traffic flows. This increased the risk of a mid-air collision'.

GAAP environments were not designed to provide strategic "separation assurance" between traffic flows. Separation within the GAAP environment was see-and-avoid and principally the responsibility of the pilot.

Post incident, the change to Class D has removed the GAAP arrival routes and although designated inbound reporting points exist, aircraft can request clearance into the airspace from any point. In addition, consequent to the change to Class D, CASA implemented a change as per AIP [Aeronautical Information Publication] ENR [En Route] 12.3.6; unless ATC [air traffic control] specifically instructs otherwise, establishment of two-way communications permits a pilot, intending to land at an aerodrome within Class D airspace, to descend as necessary to join the aerodrome traffic circuit. Thus, the current airspace design and rule set means that strategic separation between traffic flows is not possible. To improve safety at Moorabbin, Airservices has, as stated in our original response, implemented the following:

  • Traffic, staffing levels and other identified threats at Moorabbin are now routinely monitored and reviewed in conjunction with the 'Metro D' and location specific Operational Risk Assessment (ORA).
  • Increased staffing at Moorabbin has alleviated the operational need to combine positions. The ADCW [aerodrome control – west] position at Moorabbin is now routinely operated as a standalone position except where low workload allows it to be combined with other positions. This enables the controllers to provide timely traffic information to aircraft.
  • Although prior to the incident controllers were assessed on workload management, the National ATS Procedures Manual (NAPM) now provides strengthened formal traffic management guidance to controllers. It includes a list of the factors a tower controller should consider in assessing the appropriate number of aircraft for circuit operations.

ATSB response:

The ATSB is satisfied that the action implemented by Airservices Australia, in conjunction with the change of GAAP aerodromes to Class D that was implemented by the Civil Aviation Safety Authority on 3 June 2010 (see the previous section) will adequately address the safety issue.

   
Current issue status: Adequately addressed
Status justification:

The ATSB is satisfied that the action implemented by Airservices Australia, in conjunction with the change of GAAP aerodromes to Class D that was implemented by the Civil Aviation Safety Authority on 3 June 2010 will adequately address the safety issue.

 
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Last update 20 February 2014