Obstacle Limitation Surfaces (Plural)
If you work in the construction industry as a developer, builder, architect or crane operator and have worked on a high-rise project, chances are you may be familiar with the term “OLS”. The OLS, or Obstacle Limitation Surfaces (OLS), are one form of protection established by the aviation industry to protect airspace that if penetrated could compromise the safety,efficiency or regularity of aircraft operations. The OLS is often referred to as a single surface,when in reality it is made up of multiple, each with their own geometry and serving a specific purpose. The OLS Map illustrates the following surfaces with collectively form an airport’s OLS:
- Approach Surface
- Inner-Approach Surface
- Take-off Climb Surface
- Conical Surface
- Transitional Surface
- Inner Transitional Surface
- Balked Landing Surface
- Outer Horizontal Surface
- Inner Horizontal Surface
You can view the Sydney Airport OLS Map and other charts relevant to its protected airspace through this link.
Application in Australia
The International Civil Aviation Organisation (ICAO) develops and disseminates Standards and Recommended Practices (SARPs) on (among other things) how to design airports, airspace and how to conduct flying operations. Contracting States like Australia are then required (unless exemptions are sought) to implement these SARPs into their local regulatory framework. In Australia’s case, the following statutes have been enacted:
- the Civil Aviation Act 1988;
- the Air Navigation Act 1920;
- the Airports Act 1996;
- Civil Aviation Regulations (CARs), Civil Aviation Safety Regulations (CASRs) and subordinate documents such as Civil Aviation Orders (CAOs), the Aeronautical Information Publication and the like. CASA has produced documentation in the form of Manual of Standards (MOS), Civil Aviation Advisory Publications (CAAPs)s and Advisory Circulars (ACs) to assist industry stakeholders to implement the required SARPs.
Modernising the OLS
Notwithstanding current ICAO SARPs referred to above, the ICAO document “Aerodrome Obstacle Surfaces – The New Concept” by the ICAO OLS Task Force dated May 2016 provides a window into the future of airspace protection around airports. In essence, this document lays out the conceptual foundation for the comprehensive review of ICAO document suite which currently informs contracting States on matters relating to the protection of airspace and subsequently the height of terrestrial structures.
The (draft) document (emphasis added) notes that much of the origins of the architecture of the OLS originate in the 1950s and mostly reflect operational considerations at that time. Importantly, the key driver behind this review is that the OLS no longer reflects the performance characteristics of modern aircraft and air navigation systems. Although it is not the intention to merge these two sets of surfaces, the time has come to revisit the practical application of airspace protection. The document presents the vision for the future management of obstacles within the aerodrome boundary and in the vicinity of an aerodrome given that aircraft and systems performances have evolved and significantly reduced aircraft deviations from desired flight paths and considering the need to create a better economical balance between urban density and airspace. The ICAO OLS Task Force defines two new key terms for the surfaces which will collectively make up the OLS of the future:
- Obstacle Free Surfaces (OFS): shall not be penetrated, except for special considerations for existing terrain and obstacles – approach, transitional and balked landing surfaces are to be categorised as OFS; and
- Obstacle Evaluation Surfaces (OES): penetrations of these surfaces are allowed, subject to an aeronautical impact assessment (and relevant authorities) concluding the penetration will not adversely affect safety or accessibility of intended aircraft operations at a given aerodrome.
Aeronautical Study Guidelines
Overall, the new surfaces are expected to be less restrictive (i.e. narrower, steeper and shorter) than those which currently exist at aerodromes across the world. Any penetrations of the OES are to be based on the outcomes of an aeronautical study that has addressed the following:
- Identifying the hazards;
- Possible mitigations;
- Impact (cost, efficiency and safety) associated with mitigations e.g. displacing threshold, adjusting approach angle
- Impact to Communications, Navigation and Surveillance;
- Impact to Air Traffic Control Operations e.g. loss of Light of Sight;
- Aerodrome Operations (Usability, Accessibility and Efficiency)
- Environmental considerations
- Recommendation for acceptance of the aeronautical study