But no Australian government can accept the credible possibility of such a calamity occuring to a major population centre. So whilst the possibility of totally running out of water is really quite small, precautions are put in place to manage the worst credible critical scenario, simply because the consequences if its occurance are so totally devastating. Hence very expensive to build and operate desalination plants are on the menu for most mainland cities.
Aerodrome Airspace Collision Risk Reviews
R2A has been involved in a number of airport airspace risk reviews in Australia and New Zealand including Taupo, Palmerston North for the Civil Aviation Authority (CAA) and Avalon and Williamtown for the Office of Airspace Regulation (OAR). Copies of the Avalon and Williamtown studies have been published on the OAR website: www.casa.gov.au/oar/papers/index.htm
The risk approach adopted in all these studies is generative in nature focussing on precautions rather than hazards. Risk insight is based on the common law principle that all reasonable practical precautions need to be demonstrated as being in place based on the balance of the significance of the risk vs effort required to reduce it. As such the approach automatically receives the imprimatur of both High Courts (Australia and New Zealand).
This legal consistency of approach has been tested with legal counsel for both OAR and CAA. This approach paralels what R2A understands to be the intent of the safety case regime, perhaps best described by Lord Cullen (2001):
A safety case regime provides a comprehensive framework within which the duty holder's arrangements and procedures for the management of safety can be demonstrated and exercised in a consistent manner. In broad terms the safety case is a document - meant to be kept up to date - in which the operator sets out its approach to safety and the safety management system which it undertakes to apply. It is, on the one hand, a tool for internal use in the management of safety and, on the other hand, a point of reference in the scrutiny by an external body of the adequacy of that management system - a scrutiny which is considered to be necessary for maintaining confidence on the part of the public.
Such an approach suggests that the users of the airport airspace collectively determine what they believe is the appropriate level of precautions for the airport airspace. The proposal is then put up for scrutiny by the regulator and other parties who test it in various ways and if satisfactory, come to a view often expressed as: We see nothing wrong with what is proposed.
The aerodrome airspace collision risk model is an estimative risk model that demonstrates the change in risk for the addition or removal of different control options. It is designed to determine the change in risk for the various control options both at the loss of control points and in terms of an annualised estimate of persons at risk. That is, it demonstrates the relative risk balance between competing precautions.
The primary strength of the model is as communication tool that facilitates robust internal conversation at the airport between the airspace users and consequent external review. This transparency should enable defensible risk decision-making, both by airport operators and regulators.
The risk component of the studies are generally short and sharp. The New Zealand work particularly is usually completed inside a week on site with write up completed within a fortnight after that.
Considering the reviews collectively, a number of interesting insights have appeared. The threat-barrier diagram (taken from the Avalon report) demonstrates one.
As a rule, low cost high reliability arises when there are multiple, low cost independent barriers rather than a single high cost 'gold plated' barrier. Air traffic control, in the example shown, whilst obviously very effective is an expensive barrier which supplants other, individual low reliability, low cost barriers. But collectively, these low cost barriers ca n be very effective and often approach the effectiveness of a single 'gold plated' barrier.
Low reliability barriers can generally be readily enhanced with little effort and expense. A common observation by airspace users is that the protection of TCAS equipped passenger aircraft is most simply enhanced by ensuring a defined, transponder mandatory, aerodrome airspace.
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