An ATSB safety study investigation's findings contain important lessons for safety assurance in airport planning and safeguarding. It reviews the interpretation and application of Australian and international aerodrome standards, which affect how high and how close buildings can be placed to a runway.
The investigation examined historical uncertainty around the application of the aerodrome standards, and resolution by the Essendon Fields Airport operator of 'grandfathering', with the acceptance of the Civil Aviation Safety Authority (CASA), to aerodrome standards from the 1970s. Those standards had been used to determine the width of the runway strip (the rectangular surface area surrounding the paved runway) for the east-west runway 08/26. This action also determined the location of the obstacle limitation surfaces (OLS) along the side of the runway strip. The planning and approval process for the Bulla Road (DFO) retail precinct at the airport in the early 2000s was considered in the context of that historical uncertainty.
"This complex investigation made nine findings pertaining to the acceptance of grandfathering in non-standard circumstances, review of safety cases, limited guidance for some safety standards, and assurance processes between federal agencies for airport planning relating to the Bulla Road Precinct," said ATSB Chief Commissioner Angus Mitchell.
"We note that both CASA and the airport operator have maintained that there is an acceptable level of safety with the current status of the runway strip, obstacle limitation surfaces, and publication of information to pilots. It was not the role of the ATSB to do a separate risk assessment, but we have noted the type of risk information that should be taken into account by aerodrome operators and regulators."
Mr Mitchell explained that the OLS are imaginary surfaces that provide a protective buffer against obstacles, such as buildings, for aircraft in the final stages of the approach to land. Any obstacles that encroach the OLS are subject to a referral to the aviation regulator for risk assessment.
From 1971, when Essendon ceased operating as an international airport, the runway 08/26 strip width was changed from 300 metres to 180 metres. The OLS around it changed with this dimension as well. The strip width was consistently published as 180 metres. However, in 2015, CASA issued an instrument to approve obstacles and require the strip width be published as 300 metres when the standards for the 180 metre strip width were not identified. The effect was that the northern portions of the retail centre buildings (which were built in 2005) infringed the runway strip and OLS down the side of the runway strip. They were notified to pilots as obstacles.
Mr Mitchell explained that the ATSB's investigation commenced in 2018 after questions arose in another investigation as to how the buildings came to infringe the OLS. In 2019, when standards from the 1970s were identified and grandfathering occurred with the publication of a 180 metre runway strip width, the retail centre no longer infringed the runway strip or OLS.
Mr Mitchell said that the investigation had been through extensive review processes with directly involved parties, and was rescoped when grandfathering provisions were applied during the course of the investigation. Further, there were challenges with the limited information available from historical periods stretching back to the 1970s to provide context to the investigation and the need to address varying interpretations of the standards.
Separate, but in parallel to this investigation, an International Civil Aviation Organization (ICAO) taskforce has been reviewing the international standards (from which the Australian standards are derived) for the OLS. Changes have been proposed with consideration of the need to provide greater clarity on the application of the surfaces, and to reflect that modern aircraft and navigation systems have enabled reduced deviations from the intended flight path. Contracting States like Australia are considering the proposed changes.
"This investigation highlights the complex nature of airport planning and aerodrome safeguarding with the many factors that need to be considered to ensure an acceptable level of safety," Mr Mitchell concluded.
"Aerodrome planning and aerodrome safeguarding can be further complicated when applying aerodrome standards with changing design criteria over a long historical period, as was the case at Essendon Fields Airport. It is even more challenging when there are incomplete records, limited guidance on how design criteria relate to risk, and changing interpretations of standards."
