What to do after receiving a NATS TOPA - Pager Power
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What to do after receiving a NATS TOPA

What to do after receiving a NATS TOPA
January 11, 2017 Kai Frolic


NATS (formerly National Air Traffic Services) is the United Kingdom’s main air navigation service provider. It is a public-private partnership that, among other things, safeguards multiple radar installations throughout the UK. These radar installations include air traffic control radar at airports and long range en-route radar[1].

Air Traffic Control Tower

Figure 1: Air Traffic Control Tower

What is a TOPA?

Proposals for developments such as large buildings and wind farms often require an assessment of potential impacts on NATS radar. NATS can provide a Technical and Operational Assessment (TOPA) of a proposed development. This is often triggered following submission of a proposal to the Local Planning Authority (LPA).

The flowchart below sets out the aims of a NATS TOPA.

  • Whether a technical impact is possible for any radar or other navigation aids.
  • If so, whether this impact is operationally significant.
  • If the impact is significant.

NATS TOPA FlowchartFigure 2: NATS TOPA objectives flowchart

 What to do next

If NATS stipulates a mitigation requirement

Where a mitigation option is identified, it is advisable to determine and evaluate:

  • The basis for the mitigation requirement.
  • The cost of the recommended solution.
  • The process for implementation of the solution.
  • The timeline associated with implementing the mitigation.
  • Whether the technical and financial requirements appear consistent with the requirements for comparable developments.
  • Any available alternatives – whether technical or operational.

Mitigation for radar and/or navigation aids is a technically complex area. It is prudent to ensure that the matters at hand are well understood by the development team.

If NATS objects – with no mitigation option

In some cases, NATS will determine that the impact cannot be mitigated and that the development should not go ahead – and this may be the case. However, there may be further options that warrant further consideration, particularly if there is any room for manoeuvre within the development design.

If a TOPA results in an objection, it is advisable to determine:

  • The features of the development that contribute the most to the impact. For example, if one turbine out of twenty is the reason for an objection, the overall scheme may have considerable potential.
  • Whether the operational concerns are justified.
  • Whether the overall determination is consistent with comparable developments.
  • Whether any cumulative concerns are up-to-date.
  • Whether there are mitigation options that have not been considered or have been prematurely discarded.

Fact Checking


Assessment of a development’s impact on a radar network is complex for a few reasons. One is the nature of the systems involved. Another is the statistical nature of the interactions between electromagnetic signals and physical structures, particularly if they are moving. The overall result is that the severity of a predicted impact is not always black and white.

Another consideration is that the existing environment has significant influence on the result of an assessment – particularly the operational side. NATS, like anyone else, must rely on the best data available pertaining to existing and proposed developments. This can be difficult to determine with certainty because the existing environment is dynamic and databases that catalogue existing and future developments are not always comprehensive.

These factors mean that further investigation of potential hurdles can allow objections to be overcome.


A TOPA may identify an impact and prompt an objection. In many cases, informal consultation with NATS following receipt such an objection leads to further discussion of mitigation options. Viable options can be available even if none have been mentioned within the original TOPA.

Cumulative effects

Of particular note for wind farm objections, is the importance of existing and consented developments in the surrounding area. This comes into play when the cumulative effect of multiple schemes is considered. In some cases, developments that were once consented but eventually scrapped may still be factored into the initial cumulative assessment. Ensuring that the assessed cumulative environment matches the real world can be a valuable exercise if a cumulative objection is raised.


The NATS TOPA is designed to identify whether a development will cause any issues and, if so, appropriate solutions. In many cases, this is exactly what a TOPA does. However, if there is a mitigation requirement or a resulting objection, it can be worthwhile to dig deeper into the areas of contention. Engagement with NATS is key to understanding their position and overcoming any areas of concern.


[1].Note that en-route air traffic control is provided by NATS En-Route Limited (NERL) – which is a subsidiary of NATS that operates under a licence issued by the UK Civil Aviation Authority.

Image Accreditation “Under Control” by Islxndis via flickr / CC BY-ND 2.0 / Image cropped and resized from original.


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