Conclusions for Route 4 – known by some as the ‘Dorking bulge’

Conclusion of the Route 4 RNAV1 SID Monitoring Period

The re-designed Route 4 RNAV1 SID monitoring period came to an end on 26 November 2016.

Overall, our assessment of the amendment to this route, as adopted on 26 May 2016, is that it has achieved what it was required to do, in that it has shown c. 94% compliance in its track keeping within the NPR and has at the same time achieved a degree of dispersal around the route’s turn, something that was particularly requested by the local communities. I set out some other observations in the paragraphs that follow.

As a baseline track keeping conformance achieved through the conventional SID during the period May-November 2013 was 92.6%. We are confident that the Route 4 RNAV1 has delivered improved performance. Following the original RNAV1 implementation during the period May-November 2015 traffic route conformance dropped to 62.06%. Track keeping has significantly improved during this monitoring period with conformance reaching 93.95% over the period May-November 2016. In terms of air traffic movements (ATMs) although the number of aircraft flying the route during both periods was around the same – 19,792 (2015) and 19,722 (2016) – this reduced off track aircraft by 6315 ATMs.

As part of the process to ensure sufficient operational compliance GAL initially considered whether an alternate RNAV1 SID design option should be included to be used in strong south-westerly wind conditions. It transpired through discussions with operators that the windy day option would require the aircraft to be configured in such a way (ie extended flaps and increased thrust) that it would likely result in increased noise thus negating any perceived benefit from improved track keeping especially as the existing levels of compliance are relatively high (ie c. 94% over the monitoring period). Moreover given the added complexity of activating a ‘windy day’ SID we do not consider that this option would add significantly to the operational performance on this route. Therefore, unless there is a requirement, our intention is to withdraw this proposal.

GAL has, and continues to, engage directly with some operators to aid compliance including to help shape airline standard procedures but also in the case of one airline to support simulator flyability checks.

During the monitoring period complaints received in respect of this route were as follows:

Number of pieces of email feedback              16,964
Number of individual email addresses            1,863

Numbers of email addresses      Feedback Email Nos      Feedback Percentage
50 individuals responsible for          5731                    33.78%
100 individuals responsible for         7902                    46.58%
250 individuals responsible for         11824                   69.70%

Of the total number of complaints received, 4,858 (29% of the total) from 695 individuals (37% of the total), related to the overflight of Horley , as aircraft were vectored from the SID. After the adoption of this amendment, levels of vectored traffic leaving Route 4 and over flying Horley increased from historical levels of approximately 1-3% to a high of 8-9%. This is clearly an important issue but one which we consider to be separate from the route design itself. Working closely with NATS this problem has been addressed through a controller education programme as a result of which the number of Horley overflights have progressively declined since the problem was first identified. For comparison, at its worst in July 16 overflights were measured at 8.45% (420 aircraft) but December 16 was 0.57% (14 aircraft). We will continue to monitor the numbers of Horley overflights and work with NATS to ensure the highest possible level of compliance.

Although the dedicated Route 4 email address closed with effect from 23:59 on 26 November 2016, noise complaints related to Route 4 will still be captured via our dedicated noise complaint tool Casper.

2017-01-23T16:58:57+00:00 January 23rd, 2017|