The OLS are virtual surfaces not to be penetrated by new obstacles. If a structure remains below that, all is well. At least, that’s how the OLS are often applied around airports for the safety of flight operations. However, there are two significant problems with blindly following OLS limits.
For over 50 years, the Obstacle Limitation Surfaces (OLS) described in ICAO Annex 14 have been the steadfast rule for building development policies on and around airports worldwide. The generally unconditional reliance is surprising given the potential problems.
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In some cases, limitations might be too strict, negatively impacting local economic development. In others, they may be insufficient and severely impair airport safety and capacity.
Problem 1 – Obstacles above the OLS may be acceptable, even desirable
“Is penetrating the OLS a problem?” clients often ask. The answer is usually yes, for obvious safety reasons. However, a singular emphasis on flight safety can unintentionally impede the economic interests of an airport’s surroundings.
Las Vegas is a case in point. The figure above shows how Trump Tower significantly breaches the “inner horizontal surface.” And Trump Tower is just one of some 50 buildings penetrating the OLS! The enormous benefits of a business district near the airport were too important to ignore.
The city of Bern is another. Because the surrounding mountains penetrate the OLS, Bern’s airport would not even exist if OLS limits were essential for flight safety.
Problem 2 – Obstacles below the OLS may not be acceptable
There is a common misconception that obstacles below the OLS are safe to build. In our projects, we encounter flight procedures that require even lower height limits. We also see obstacles well below the OLS disrupting communication, navigation, or surveillance systems (CNS).
New obstacles below the OLS are often permitted without further analysis, and seldom reported to the obstacle database. And even then, a new analysis of CNS signals or PANS-OPS safety margins is seldom triggered. It can take years before anyone finds the conflict. Solutions after the fact are expensive: remove the obstacle or change flight procedures (and potentially decrease capacity).
Solving the problems
To us, Annex 14 without further analysis cannot dictate effective obstacle limitations. Integrating surfaces for PANS-OPS and CNS into policies, including incorporating capacity for growth, would significantly decrease risks.
With broader analysis, aviation authorities can avoid a too-strict application of the OLS stifling development. Cities like Las Vegas and Bern illustrate how carefully designed flight procedures can guarantee PANS-OPS (ICAO) or TERPS (FAA) flight safety standards, even when not adhering to the OLS.
For airports, broad analysis addresses the serious issue of disruptive obstacles forcing costly, complicated changes to flight procedures. After all, reduced capacity and writing off expensive CNS installations are not desirable results.
(Read about OLET, our Obstacle Limitation and Evaluation Tool.)
About To70. To70 is one of the world’s leading aviation consultancies, founded in the Netherlands with offices in Europe, Australia, Asia, and Latin America. To70 believes that society’s growing demand for transport and mobility can be met in a safe, efficient, environmentally friendly and economically viable manner. For more information, please refer to www.to70.com