Campaigners criticise CAA’s PIR report on Luton flight path changes and noise increase

The CAA have published the results of a post-implementation review (PIR), which analysed the impact of RNAV between its introduction in 2015 and 2017. RNAV means concentration of planes down a narrow flight path, intensifying noise for those over-flown. The CAA concluded that the airspace change “achieved the objectives set out in the original proposal”.The introduction of RNAV has meant the majority of departures have moved closer to Harpenden, south Harpenden and the less densely-populated areas of Redbourn, while still not to flying directly over those areas.  The number of flights increased by 30% between 2015 and 2017, but the PIR says the flight paths was not an “enabler” for an increase in airport capacity, or for an increase in flights during the early morning and late evenings. The CAA says the increase in noise complaints 2015 – 2017 was due to there being more planes – not the narrowing of the flight paths. Local campaigners are angry and disagree with the CAA, saying much of the noise nuisance is due to RNAV, not just more flights.  Andrew Lambourne (LADACAN) commented: “The whole thing feels like a rubber-stamping exercise, and was not worth waiting three years for.”

See a detailed explanation of what has been going on – below.

Local campaign group LADACAN wrote:

The CAA have published the results of a post-implementation review (PIR), which analysed the impact of the first RNAV concentrated flight route at Luton Airport. The system was introduced in 2015 but technical issues with Boeing aircraft not being able to engage with its first technically challenging waypoint meant the assessment did not start until 2017. By that time there had been a substantial rise in complaints – but also, due to financially incentivised growth at Luton, a substantial rise in aircraft movements as well.

Concentrated tracks may or may not deliver benefit to people on the ground. If they enable aircraft consistently to avoid communities and fly instead over non-noise sensitive areas, they can be a good. But if they avoid (naturally noisier) towns in order to fly over (naturally quieter) rural villages, they can be a curse for the fewer to benefit the many – but the many may mainly benefit at night when the town is also quieter.

The potential worst of all worlds can occur if the concentrated track threads between tightly spaced communities – say half a mile apart. At altitudes of around 5-6,000ft a concentrated swathe may well sideways-radiate noise into the communities (see CAA’s CAP 1498) even if they are not directly overflown.

In the case of the Luton implementation of RNAV, the airport operators led communities to expect noise reduction flowing from a significant reduction in overflying: 30,000 overflown would, they said, reduce to 3,000. For those not versed in all the technicalities, this seemed a reasonable deal. Furthermore, said the airport, the centre line would move a little south of its existing position south of Harpenden, so that planes turning the corner would be more likely to be able to follow it. Again, sounds like a good deal.

The paradox was that most of the planes missed the original centre line by a significant distance (in some cases a literal mile) and so when the RNAV waypoint and the reduction in speed enticed them back onto the new centre line, a whole load of aircraft moved north, and because audible and visible in south Harpenden whereas previously they had visited the sky over north Hemel Hempstead. So, not such a good experience as folk had been led to believe.

By way of second whammy, it turned out that NATS air traffic controllers were and still are still “vectoring” a proportion of the flights directly over Harpenden and St Albans, hence the claim of massive reductions of people overflown rings hollow – and of course there is no real definition of how many flights a day have to come directly over your house for you to count (to an Airport or the CAA) as being overflown.

And by way of third whammy, those planes that stay in the swathe then thread through that narrow 1km gap between Harpenden and St Albans. People on the fringes of both communities now probably perceive all of them since the swathe is not by any means pencil-thin but wobbles around due to the wind (we are told) and covers more than the 2km maximum which was promised. Previously, the greater spread may well have resulted in people only being aware of say half the passing flights, some of which would have been directly overhead and say 3dB louder, others to the side and slightly quieter, others in the distance and not a problem. This is the whole “concentration” issue: the experience of each aircraft transit is broadly the same – great if you are nowhere near them, maddening if you are.

Finally, Sandridge is now directly overflown by the centre line. The Airport had tried to create a baseline noise measure before RNAV but its monitoring was somehow faulty and it ended up with a noise sample histogram where the quieter half of the readings were entirely missed off. Ergo, the baseline was an average of the noisier flights only, hence high. And hence when the Airport measured again in 2017 and this time did not miss off the quieter flights, magically the noise averages came down and the CAA fell for this and did not question the dodgy histogram, and declared that noise in Sandridge had not increased. In doing so it ignored completely the question of concentration – which does not say much for the CAA PIR team’s understanding of aircraft noise impact.

So overall the CAA rubber-stamped the implementation, while drawing attention to the continued vectoring and the failure to constrain to the promised 2km swathe. Campaign groups who spent 3 years waiting for this review feel that the CAA has dodged the harder questions raised above completely, and has fallen for a crass error in a noise monitoring exercise which even a GCSE student could have spotted.


St Albans campaigners slam report on Luton Airport flight path changes

10 February 2020

By Anne Suslak  (The Herts Advertiser)

A survey into Luton Airport’s flight paths has found they met their objectives in mitigating the impact on St Albans district – despite opposition from noise campaign groups.

The RNAV GPS navigation system was introduced in 2015 and narrowed flight paths, which anti-noise campaigners said simply concentrated noise pollution from flights over a smaller area.

The Civil Aviation Authority (CAA), have published the results of a post-implementation review (PIR), which analysed the impact of RNAV between its introduction and 2017.

The report concluded that the airspace change achieved the objectives set out in the original proposal.

A CAA spokesperson said: “The purpose of a Post Implementation Review is for the CAA, as the independent regulator, to assess whether the change has delivered the anticipated impacts and benefits set out in the original airspace change proposal and decision, and if not, to ascertain why and determine the most appropriate course of action.

“It is not a review of the decision itself, and neither is it a re-run of the original decision process.”

The report found that the introduction of RNAV reduced planes directly flying over Redbourn, Hemel Hempstead and the southern areas of St Albans. As a consequence, however, the CAA found that the majority of departures had moved closer to Harpenden, south Harpenden and the less densely-populated areas of Redbourn, while still managing not to fly directly over those areas.

Aircraft movements increased by 30% between 2015 and 2017, but the report claimed changing the flight paths was not an “enabler” for an increase in airport capacity, or for an increase in flights during the early morning and late evenings.

Therefore the report claimed the increase in noise complaints during that period was due to an increase in air traffic – implemented by the airport and its parent company London Luton Airport Limited (LLAL) – not the narrowing of the flight paths.

St Albans MP Daisy Cooper has slammed the CAA report as “passing the buck” by laying the blame of aircraft noise elsewhere.

She said: “This report is a blatant attempt to pass the buck as residents are being left to suffer as different authorities play the blame game.

“The CAA is taking the stance that they are responsible for the routes, not how many aircraft use the routes, which is a planning matter for Luton Borough Council and government policy.

“I have secured a meeting with the aviation minister and we will be raising our concerns in the strongest possible terms.”

Anti-noise campaigners have also criticised the report for blaming the rise in complaints on an increase in flights, without acknowledging their belief that concentrating the flight paths exacerbated the problem.

John Hale, of St Albans Quieter Skies, said: “We are very disappointed by the CAA report. By blaming the increase in complaints just on the increase in flights, it ignores the fact that concentration makes people aware of many more aircraft, even though less may be going directly overhead. They’ve chosen the easy option to avoid looking into the real issue of whether concentration is a good thing or not.

“The CAA has also sidestepped the question about whether flights from London Luton Airport have more adversely impacted our communities since the introduction of RNAV.

“The report focuses only on the technicalities, and does not test all the claims by the airport about the noise reductions which would result from its introduction.

“Given the overall bad experience of the last four years, proposed additional expansion of the airport will just further damage our environment.”

The CAA acknowledged that aircraft are still being dispersed over St Albans and south Harpenden, and reported a large reduction in noise over Sandridge – the accuracy of which has been disputed by campaigners.

Andrew Lambourne, of campaign group LADACAN (Luton and District Association for the Control of Aircraft Noise), said: “The assessment conveniently ignores the CAA’s own guidance for what counts as an overflight: when an aircraft passes close by it is about as noisy as when it is directly overhead, making concentrated tracks close to communities a menace.

“The CAA has dodged all the difficult issues we raised with them in 2017.

“The whole thing feels like a rubber-stamping exercise, and was not worth waiting three years for,” he added.