In August 2025, ICAO adopted Amendment 18 to Annex 14, introducing a new, modernised Obstacle Limitation Surfaces (OLS) framework, representing the most significant change to aerodrome safeguarding in decades. The new OLS becomes applicable globally from 21 November 2030.
These changes affect all UK aerodromes, safeguarding authorities, developers, and organisations involved in airspace protection, obstacle assessment and planning.
The new framework replaces the long‑standing traditional OLS with a performance‑based, operations‑driven model, reflecting advances in aircraft performance, navigation, and procedure design.
Overview of the New OLS Framework
The previous ICAO OLS (in use since the 1950s) has been restructured into two major categories:
1. Obstacle Free Surfaces (OFS)
These surfaces ensure a kept‑clear volume of airspace where no obstacles are permitted, except existing terrain or previously assessed objects.
They are closely linked to:
- runway type
- aircraft Aeroplane Design Group (ADG)
- standard operations such as approaches, go-arounds, balked landings and take-off climbs
These surfaces represent the mandatory protected airspace needed for safe aircraft operations.
Key features include:
- Stricter obstacle control close to the runway
- Harmonised approach, transitional, and take-off climb surfaces
- Applicable to all runway types, not only precision runways in the old system
2. Obstacle Evaluation Surfaces (OES)
Instead of prohibiting obstacles outright, OES surfaces operate as triggering surfaces:
- If an obstacle penetrates an OES, it triggers an aeronautical study rather than automatic rejection.
- This reflects modern risk‑based and performance‑based evaluation principles.
OES account for:
- published instrument flight procedures
- aircraft performance
- operational intent
- ADG classification
- visual circuit patterns at aerodromes without procedures
This represents a major shift: penetration is manageable, not automatically unsafe, provided mitigations are established.
Aeroplane Design Group (ADG) – A Key Change
The new OLS is tied to the ICAO Aeroplane Design Group (ADG) classification, reflecting:
- aircraft wingspan
- indicated speed at threshold (Vat)
Each ADG has corresponding OFS and OES dimensions.
This approach is more tailored to actual aircraft performance, improving safeguarding accuracy and avoiding unnecessary protected volumes at aerodromes that do not handle larger aircraft.
What the New OLS Means for UK Aerodromes
Aerodromes will need to:
- Update safeguarding maps and digital airspace models
- Understand differences in protected volumes (some areas expand, others reduce)
- Assess impacts on development proposals and planning safeguarding processes
- Coordinate with local planning authorities
- Review existing obstacles and update obstacle databases
- Implement new ADG‑based surface modelling
- Plan for transition ahead of 2030 applicability
The new OLS may reduce safeguarding burdens in some cases (less protected airspace), while expanding them in others.
Events, Workshops and Webinars
Upcoming New ICAO OLS Workshops
To support industry readiness ahead of the 21 November 2030 applicability date for the new ICAO Obstacle Limitation Surfaces (OLS), the CAA will be delivering a series of workshops throughout the year. These sessions are designed for aerodrome operators, safeguarding teams, planners, ANSPs, developers, and other stakeholders involved in obstacle management.
Confirmed Workshops
- 3 June 2026 – Manchester
- 17 July 2026 – Gatwick
- 8 October 2026 – Glasgow
Registration for this workshop is currently register‑interest only. Confirmation of available places will be emailed shortly to those who register.
What to expect from the workshops
Participants can expect sessions covering:
- Understanding and applying Obstacle Free Surfaces (OFS) and Obstacle Evaluation Surfaces (OES)
- Transition planning and implementation timelines
- Practical safeguarding case studies
- Interpreting ADG‑based surface changes
- Impacts on planning, development, and aeronautical studies
New OLS Webinar (Recording to be uploaded)
We are preparing a full webinar that introduces the new ICAO OLS framework, outlines the key changes, and explains what aerodromes and stakeholders need to do during the transition period.
Once complete, the webinar recording will be uploaded here, alongside:
- Presentation slides
- Q&A summary
- Supporting documents and guidance
This will allow stakeholders to access the material on demand and share within their organisations.
Stay Informed
We encourage stakeholders to revisit this page for updates as we release:
- Additional webinars
- Workshop materials
- Implementation guidance
- Transition resources
Why did ICAO update the OLS?
The previous OLS structure dates back to the 1950s and no longer reflects modern aviation operations. Updates were required due to:
- Improved aircraft navigation and avionics
- Steeper climb and approach capabilities
- Need to align OLS with PANS‑OPS surfaces
- Increased urban development pressures
ICAO identified the need for more adaptable, harmonised, and performance‑based safeguarding criteria.
How do the new OLS interact with PANS OPS surfaces?
Although the frameworks serve different purposes, ICAO’s update intends to better harmonise OLS with PANS‑OPS. The new OLS approach recognises that OES (evaluation surfaces) may overlap with or influence instrument procedure design, creating a more consistent safeguarding boundary.
This aligns with ICAO’s goal of improving the synergy between design surfaces across Annex 14 and PANS‑OPS.
How will existing obstacles be treated under the new OLS?
Existing terrain and objects may remain within Obstacle Free Surfaces (OFS) if already assessed but will require a fresh review under the new methodology. OFS permits existing obstacles in limited circumstances, while OES may require an aeronautical study if these obstacles intrude into evaluation volumes.
Will aerodromes need to resurvey their obstacle environment?
Most aerodromes will need to update obstacle surveys to align with ADG‑based modelling and the new OFS/OES geometry, which differs significantly from legacy surfaces. Updated geospatial data is essential for accurate safeguarding and for evaluating OES penetrations within the revised framework.
GIS tools such as ArcGIS Aviation now support the new models.
How will the changes impact safeguarding maps submitted to planning authorities?
Aerodromes will need to provide updated maps reflecting:
- new OFS volumes
- new OES triggering surfaces
- ADG‑based protection areas
This means existing safeguarding maps used in planning systems will need complete revision.
How do Aeronautical Studies under the new ICAO OLS compare to the safeguarding assessments we do today?
Under the new ICAO OLS, an aeronautical study is required whenever an obstacle penetrates an Obstacle Evaluation Surface (OES). Importantly, penetration of an OES does not automatically mean the obstacle is unacceptable; instead, it triggers a structured safety assessment to determine whether mitigation measures or procedural adjustments can maintain safety. This mirrors the type of safeguarding assessments carried out today for obstacles that affect current OLS or PANS‑OPS surfaces.
In practice, an aeronautical study under the new OLS will still include:
- reviewing the operational impact on aircraft performance
- assessing visibility, navigation, and missed‑approach implications
- evaluating whether procedural or operational mitigations can maintain safety
- determining whether the obstacle can remain, be reduced, or be restricted
ICAO describes the OES as “triggering surfaces” designed specifically to initiate this kind of evaluation, rather than impose an automatic prohibition, which is consistent with how UK safeguarding teams already handle assessed penetrations today.
This means that for most aerodromes, aeronautical studies under the new OLS will feel familiar, because the methodology, evidence base and decision‑making process closely resemble existing safeguarding assessments.