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UK Civil Aviation Regulations

These are published by the CAA on our UK Regulations pages. EU Regulations and EASA Access Guides published by EASA no longer apply in the UK. Our website and publications are being reviewed to update all references. Any references to EU law and EASA Access guides should be disregarded and where applicable the equivalent UK versions referred to instead.

Annex 15 (Aeronautical Information Services) to the International Convention on Civil Aviation defines obstacles as:

“All fixed (whether temporary or permanent) and mobile objects, or parts thereof, that:

  • are located on an area intended for the surface movement of aircraft; or
  • extend above a defined surface intended to protect aircraft in flight; or
  • stand outside those defined surfaces and that have been assessed as being a hazard to air navigation.”

To ensure flight safety, operators/developers of obstacles in the UK that meet any of the above criteria are required by UK legislation to notify the Civil Aviation Authority (CAA) and/or relevant aerodromes.

Obstacle categories

Obstacles can broadly be categorised as either aerodrome obstacles or air navigation (en-route) obstacles.

Aerodrome obstacles

  • An aerodrome obstacle is one that is located on an area intended for the surface movement of aircraft or that extends above a defined surface intended to protect aircraft in flight. Obstacle limitation surfaces can extend to distances greater than 15 kilometres from the runway thresholds.
  • Details of aerodrome obstacles selected as significant are likely to be initially promulgated through the issue of a NOTAM. If the obstacle is of a long-term or permanent nature, it will subsequently be listed in the Aerodromes (AD) Section of the UK Aeronautical Information Publication (AIP) (available on the NATS Aeronautical Information Service (AIS) website) and shown on Aerodrome and Instrument Approach Charts where these have been published in the UK AIP.
  • In all cases, aerodrome safeguarding responsibility rests with the aerodrome licence holder/operator, not the CAA. More information can be found in CAP 738: Safeguarding of Aerodromes. The operator/developer must ensure that positive responses are received from all affected aerodromes before erecting an obstacle in a safeguarding area.
Close Aerodrome obstacles

Air navigation (en-route) obstacles

  • Article 225A of the Air Navigation Order (ANO) 2016 (as amended) mandates the requirement for the CAA to be notified of any existing or proposed en-route obstacles (permanent or temporary) which (or will) attain or exceed a height of 100 metres (m) / 328 feet (ft) Above Ground Level (AGL). Proposed changes to any existing en-route obstacles which (or will) attain or exceed a height of 100m / 328ft AGL must also be notified. This mandatory requirement applies to all land-based obstacles and also to all obstacles in UK territorial waters that meet the above criteria.
  • Persons in charge of relevant existing or proposed off-shore obstacles outside UK territorial waters, but within the UK Flight Information Regions (FIRs) and Exclusive Economic Zone within the Norwegian FIR are also strongly recommended to notify the CAA in accordance with Article 225A of the ANO.
  • An Aeronautical Information Circular (AIC) (in the Pink (Safety) series) has been published detailing ANO Article 225A and the associated procedures for notifying en-route obstacles to the CAA. The AIC is available on the NATS AIS website.
Close Air navigation (en-route) obstacles

Notifying the CAA

Please refer to the guidance available on our Obstacle notification webpage.

Close Notifying the CAA

Contact us

If you have any questions, please contact Airspace Regulation between the hours of 08:30 and 16:30 Monday to Friday (excluding Public Holidays).  It may not be possible to action messages/notifications submitted after 16:00 until the next working day.

Planned periods of extended closure of the Airspace Regulation section will be notified here: