Skip to content

AEF response to CAA consultation on revision of the DfT’s Public Safety Zone Policy

22nd December, 2020

In November 2020, the Civil Aviation Authority (CAA) published a consultation on proposals to amend and simplify aerodrome Public Safety Zones. AEF’s response to the consultation can be read here.

Non-technical summary:

What are Public Safety Zones (PSZ)?

PSZs are areas of land at the ends of the runways at the busiest airports, within which development is restricted in order to control the number of people on the ground at risk of death or injury in the event of an aircraft accident on take-off or landing. During these phases, pilots have less time to respond to any system malfunction or pilot error, so there is a greater risk of a plane-crash, injury and death.

What protection is there within PSZs?

The long-standing core policy objective is to control the number of potential casualties by limiting the number of people living, working or congregating in these zones by restricting development within them.  

How are PSZs constructed?

Currently, PSZs are determined by ‘risk modelling’ undertaken by NATS (formerly the CAA’s National Air Traffic Services). For each airport, a ‘statistical crash rate’ expressed in terms of the number of crashes per million movements, plus the forecast annual number of movements, are the two key variables that are fed into mathematical models to produce risk contours. These contours are lines of ‘equal’ annual individual risk that, crucially, grow or shrink in length as crash rates and the projected annual number of movements grow or shrink.   

This process has survived expert scrutiny for two decades and is used by the DfT (Department for Transport), as well as by Local Planning Authorities that are required to show that their planning permissions for airport operations will not result in the breaching of the Government’s maximum tolerable level of individual third-party risk which remains at 1 in 10,000 per year.

Why are things changing?

NATS is withdrawing this risk-modelling service, so a new process is needed to replace it.

What has been proposed?

While the CAA (Civil Aviation Authority) has proposed that the above core policy objective be retained, they are looking to change how the lengths of PSZs are established. Their intention is to replace the individually calculated PSZs for each airport with a universal ‘fixed inner-zone’ of 500 metres and a ‘fixed outer-zone’ of 1,000 metres, or 1,500 metres if projected movements exceed 45,000 per annum. These fixed zones – which address risk to people on the ground – are to be linked to hitherto separate safeguarding criteria that ensure potential obstacles do not penetrate the air corridors that aircraft use – which addresses risk to just aircrew and passengers. AEF argues that there is no convincing rationale for this new linkage, nor for the chosen lengths of the zones, and it could compromise the effectiveness of the policy’s objectives.  

Does it matter if the old and new zones differ in size?

Yes. Where the new fixed zones are shorter than existing modelled contours, as might be expected in most cases, the land-use safety measures will be less cautious. Under these circumstances AEF believes that public confidence in the PSZ policy will be maintained only if the CAA can bring forward evidence supporting its assertion that flying is now more safe, and then to remodel the contours to show that their fixed-zone replacement is a prudent step.

As mentioned above, the CAA has proposed a 500m step-change in the length of the outer fixed PSZs, which would apply at a 45,000 (per annum) aircraft movement threshold. AEF says that this is not sufficient acknowledgement of the increasing risk of a crash as the numbers of flights increase, which should continue to be explicitly acknowledged in the revised guidance.

What does AEF recommend?

If, despite these issues, the DfT adopts fixed zones, AEF recommends that they are based on existing PSZs, as long as they have been in place for at least the past seven years. AEF concludes that should NATS’ risk modelling no longer be available, then an acceptable solution would be to adopt IPPR (Institute for Public Policy Research) proposals that entail the establishment of zones defined by noise and health criteria as well as third-party risk.