Recommendation R20040056

Recommendation issued to: Airservices Australia, AirServices Australia

Recommendation details
Output No: R20040056
Date issued: 04 May 2004
Safety action status: Monitor
Background: Why this Recommendation was developed

Output text

Safety Recommendation

The Australian Transport Safety Bureau recommends that Airservices Australia estimate the overall midair collision risk at major general aviation airports (Archerfield, Bankstown, Jandakot, Moorabbin and Parafield) and compare these estimated risk levels with relevant acceptable risk criteria.

Initial response
Date issued: 29 June 2004
Response from: AirServices Australia
Action status: Monitor
Response text:

I refer to the ATSB investigation report into the May 2002 accident at Bankstown airport. Specifically, I refer to recommendation 20040056 and our considerations of this matter.

While to the uninformed, the recommendation looks to be innocuous, it involves some fairly complex issues and can not be easily or quickly dealt with.
The recommendation involves two separate issues, the estimate of the midair collision risk at the major GA airports, and the identification of acceptable risk criteria.

Apart from simply plucking a number out of the air, the only way we can effectively estimate the midair collision risk is to develop a mathematical model that could be applied to the major GA airports. The model would have to be tailor made to cater to the specific environment, procedures and traffic mix found at those airports and would involve a number of assumptions and estimates.

Collecting the data to input to a collision risk model of the type referred to above would also be difficult, as the recommendation does not distinguish between aircraft operations while the towers are manned (GAAP), and operations during the time the towers are closed (MBZ). We would have to undertake special out of hours aircraft activity monitoring and develop the model in such a way that it could cater to both types of operations.

The matter of identifying appropriate acceptable risk criteria, is a slightly easier issue to deal with, but has one draw back. As you are aware, we do not currently accept the proposed CASA acceptable risk criteria as we believe it has particular technical problems. We could, and probably will develop our own acceptable risk criteria, however, this will leave us with a criteria that has little independence. We will discuss this matter further with CASA.

From the internal discussions we have had so far, we have concluded that employing a consultant to undertake much of the work would be the most efficient way to proceed. However, we have also concluded that the process will take something in the order of six months and costs tens of thousands of dollars. With these resource issues in mind, we are wandering as to the worth of the final product.

In spite of the time and money spent on pursuing this issue, the final product will be little more than a number that, provided we don't have any significant changes to any of the contributing variables may give us a reliable risk metric. The concern is that the process of estimating and validating the risk metric will consume a reasonably large amount of time and resource, while adding little or nothing to the safety of our operations. I can't help thinking the time and resources could be better used on other projects.

We have not yet made a clear decision about our final response to the recommendation. However, we felt it was necessary to give you an undertaking that we are actively considering it.

Further correspondence
Date issued: 03 August 2009
Response from: Airservices Australia
Response status: Closed - Accepted
Response text:

As you are aware, Recommendation R20040056 requested that Airservices estimate the overall midair collision risk at the General Aviation Aerodrome Procedures (GAAP) locations.

As stated in our interim response to the Recommendation, the development of a mathematical model to estimate this risk would need to encompass operations outside of the hours of coverage as well as those when the GAAP towel is manned.

I would suggest that the solution to this would be the development of defined minimum safety standards which, before they are exceeded, initiate airspace change to mitigate risk.

As the service provider we would like to suggest that the development by CASA of the CASR Part 71 would establish a framework of minimum standards.

We also wish to formally advise that the regulatory responsibility for this recommendation resides with CASA as the airspace regulator as of 1 July 2007. We are also happy to participate in any discussions and provide assistance where appropriate.

Civil Aviation Safety Authority (CASA) actions:

On 21 July 2009, following a number of reviews of General Aviation Aerodrome Procedures (GAAP) aerodromes the Director of Aviation Safety, CASA, issued a legal direction to Airservices Australia to implement United States (US) style Class D procedures at all GAAP aerodromes as well existing Class D aerodromes and Avalon aerodrome effective 3 June 2010.

The Office of Airspace Regulation (OAR) conducted a Post Implementation Review (PIR) ( to evaluate the new Class D procedures at all new and existing Class D aerodromes and determine the need for any additional actions or improvements to these procedures.

ATSB comment:

As a result of these changes the ATSB has classified the recommendation as Closed- Accepted.

Last update 23 December 2011