LONGSTONE CORNWALL AIRPORT NEWQUAY AVIATION IMPACT REVIEW - COMMERCIAL-IN-CONFIDENCE
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Version 1.1
02/09/2020
Authors: LONGSTONE
Ian Fletcher
CORNWALL AIRPORT NEWQUAY
AVIATION IMPACT REVIEW
A report for
COMMERCIAL-IN-CONFIDENCE
Tel 07971 780936
Email: Info@windbusiness.co.uk Wind Business Support Ltd, Oxon OX12 9PZ, UK - Co. Number 08305860
Longstone – Cornwall Airport Impact Review Version 1.1 CONTENTS Introduction ................................................................................................................................... 1 Details of the proposed turbines.................................................................................................... 2 OLS Infringement ........................................................................................................................... 3 OLS Assessment.......................................................................................................................... 4 Obstacle Environment ................................................................................................................ 4 IFP Impacts ................................................................................................................................. 5 Turbine Marking ......................................................................................................................... 5 Radar Impacts................................................................................................................................. 6 Radar settings ............................................................................................................................. 6 False Track Generation (False Alarm Rates) ............................................................................... 6 Conclusions .................................................................................................................................... 8 INTRODUCTION Wind Business Support were commissioned by Clean Earth Energy Ltd to review the potential impacts of their proposed Longstone site on the infrastructure and operations of Cornwall Airport Newquay. This report presents the assessment and conclusions of work conducted over a long period of working with both Clean Earth Energy and Cornwall Airport Newquay. The focus of the assessment and discussions are those issues of concern raised by the airport from the outset of consultations with them. Whilst this assessment is primarily concerned with the specifics of the proposed Longstone turbine, it also considers the influence of additional turbines. 02/09/2020 Page 1 of 8
Longstone – Cornwall Airport Impact Review Version 1.1
DETAILS OF THE PROPOSED TURBINES
PROPOSED LONGSTONE TURBINE
Location Tip height Ground elevation*
SW 98316 55310 135m 248m
*Subject to survey and micro-siting
Turbine location on OS 1:50,000; © Crown copyright. All rights reserved. License number 100040585
EXISTING/OPERATIONAL TURBINES
Turbine ID Tip Height Easting Northings 100km NGR Base Tip Elevation
(m) Elevation (m) (m AOD)
Gunheath 77 200613 056812 SX 00613 56812 254 331
Qaurry
Higher 77 198780 054963 SW 98780 54963 218 295
Goonamarth
Greensplat 61 200063 054587 SX 00063 54587 249 310
Blackpool 77 198272 053612 SW 98272 53612 178 255
Quarry
02/09/2020 Page 2 of 8Longstone – Cornwall Airport Impact Review Version 1.1 Site location on CAA 1:250,000 VFR chart; © Crown copyright. All rights reserved. License number 100040585 OLS INFRINGEMENT Obstacle Limitation Surfaces (OLS) are defined for all licensed runways. The specific details of OLS depend upon the runway physical characteristics and use. OLS dimensions are defined in the CAA publication CAP168, ‘Licensing of Aerodromes’. OLS are used to assess the significance of any existing or proposed object within the aerodrome boundary or in the vicinity of the aerodrome particular to a runway and its intended use. Where an object infringes, or penetrates, an OLS, consideration then needs to be given to the significance of the infringement in terms of aircraft movements in the area, safe separation distances and hence its acceptability or otherwise together with any appropriate mitigation measures. Of key importance in this case is the existing obstacle environment. In ideal circumstances all the surfaces will be free from obstacles but when a surface is infringed, any safety measures required by the CAA will have regard to: a) the nature of the obstacle and its location relative to the surface origin, to the extended centreline of the runway or normal approach and departure paths and to existing obstructions; b) the amount by which the surface is infringed; c) the gradient presented by the obstacle to the surface origin; d) the type of air traffic at the aerodrome; and e) the instrument approach procedures published for the aerodrome. Safety measures could be as follows: a) promulgation in the UK AIP of appropriate information; b) marking and/or lighting of the obstacle; c) variation of the runway distances declared as available; d) limitation of the use of the runway to visual approaches only; e) restrictions on the type of traffic. 02/09/2020 Page 3 of 8
Longstone – Cornwall Airport Impact Review Version 1.1 OLS ASSESSMENT The OLS are defined in accordance with the runway physical characteristics. The airport runway 12/30 has a maximum declared distance of 3044m (rwy 30 TODA), making it a code 4 instrumented runway. The proposed turbine lies at a range of 13.0km from the runway threshold and 14.2km from the runway reference point, placing it under the Outer Horizontal Surface and the Approach Surface. The turbine tip height is 383m (1257ft) AOD. OHS The Outer Horizontal Surface (OHS) extends at a level of 267m AOD, out to 15km from the runway reference point. The turbine penetrates this surface by 116m. Approach Surface The approach surface is horizontal at the same elevation as the OHS at the point of the turbine. It has a width of approximately 3500m each side of the runway centre-line at the range of 13km from the runway threshold. The turbine lies approximately 1810m from the runway centre-line and hence the turbine penetrates the approach surface by the same amount as the OHS, ie 116m. OBSTACLE ENVIRONMENT Proposed turbines and existing obstacles: CAA VFR chart 1:250,000 The proposed turbine lies in an area of existing obstacles, having a maximum height of 1286ft (392m) AOD. This highest obstacles is directly on the approach path to runway 30. It penetrates the OHS and approach surface by 125m. The proposed turbine does not affect the minimum altitude for aircraft either flying on an approach to runway 30 or transiting south to north across the existing obstacle field. The minimum altitude is set by the highest significant obstacle. 02/09/2020 Page 4 of 8
Longstone – Cornwall Airport Impact Review Version 1.1 Further analysis of the operational impact of the proposed turbine as a physical obstruction is covered in a separate report by Cyrrus. IFP IMPACTS One of the functions of the OLS is to safeguard the Instrument Flight Procedures (IFP). In the case of Cornwall Airport, the IFPs have already been designed to prevent any conflict with the existing obstacle on the approach path of height 1286ft. Instrument Flight Procedures must be designed and assessed by organisations approved by the CAA. Cyruss is a CAA approved IFP design organisation and it has assessed the proposed turbine for impacts to the IFPs. This is the subject of a separate Cyruss report; which determined no impacts to the IFPs. TURBINE MARKING The proposed wind turbine, as an obstacle, should be promulgated through the usual channels to ensure that it appears on all relevant charts and databases. In addition consideration should be given to the need for aviation lighting, at the discretion of the airport. Such lighting would operate either continuously or from dusk until dawn and in conditions of poor visibility. As such the lighting primarily serves to alert IFR traffic, but can highlight obstacles in unpredictable conditions where VFR traffic has found it necessary to reduce height. Promulgation of wind turbine developments The need to promulgate the existence of tall structures that might constitute a significant aviation obstruction is self-evident. LPAs routinely advise the DGC (Defence Geographic Centre). Through the updated promulgation of a database document, the SARG Aeronautical Charts and Data section is advised of all such developments and update aviation charts accordingly. All structures (including wind turbines and anemometer masts) in excess of 300 ft in height are depicted on charts and details of each wind turbine are promulgated in the UK AIP, ENR 5.4 (CAP 32) 9.2. By exception, structures less than 300 ft high may be promulgated for civil aviation en-route purposes if their presence is deemed to be of navigational significance. Lighting The current requirements for lighting onshore are specified by law in the Air Navigation Order (2016) Article 222. This requires that all obstacles over 150m above ground level are fitted with medium intensity steady red lights positioned as close as possible to the top of the obstacle. In this case the turbines are below 150m tall and there is therefore no statutory requirement for them to be lit. It is principally for the airport to initially decide if there is a specific requirement for lighting the turbines because of their height and location. The CAA will provide advice and recommendations regarding any extra lighting requirements for aviation obstruction purposes where, owing to the nature or location of the structure, it presents a significant hazard to air navigation. However, in general terms, structures less than 150 m (492 ft) high, which are outside the immediate vicinity of an aerodrome, are not routinely lit; unless the ‘by virtue of its nature or location’ argument is maintained. If the airport suggests and can support such a need, the CAA (sponsor of policy for aviation obstruction lighting) would wish, in generic terms, to support such a claim. However, this would only be done where it can reasonably be argued that the structure(s), by virtue of its/their location and nature, could be considered a significant navigational hazard. 02/09/2020 Page 5 of 8
Longstone – Cornwall Airport Impact Review Version 1.1
RADAR IMPACTS
Early dialogue with the airport, subsequent meetings and a report produced by APD, determined that the airport
considered radar impacts not to be of concern. Subsequently the airport has asked Cyrrus to consider the turbine
separation required to prevent track initiation. This is the issue addressed in this section.
It is important to note that this was identified by the airport as of importance in the event of an application for
multiple turbines, or upon submission of a subsequent application in the case of a single turbine application. It has
been agreed with the airport that a radar assessment is required before any additional turbine applications,
subsequent to this one.
The Primary radar is a Selex ATCR-33. The display is plot and track extracted, meaning it only displays returns that
it can associate with a track.
The radar also has Moving Target Detection (MTD). From the observations of airport air traffic controllers, the
MTD filter appears to be effective in removing returns from isolated single turbines. Consequently, a false track
will only be generated by wind turbines when they are sufficiently close to one another for their returns to be
associated as a moving aircraft, such that a track is initiated.
Note that this will also only occur when the turbines generate returns on consecutive scans. In the event that a
track is initiated it will be displayed as a primary only return. This track will disappear if the turbines don’t generate
returns to sustain it. This will invariably happen at some point as turbines do not always generate returns even at
the most problematic yaw angle relative to the radar sensor. Most radars have a coast function, meaning that they
will look for a return that can be associated with an established track for 2 or three scans before dropping the
track in their internal processing. No returns would be displayed during coasting, only associated real returns will
be displayed.
The remainder of this section considers radar clutter generation, through track initiation, as the impact of concern
raised by the airport. The scope is limited to this issue on the basis of airport Air Traffic Controller observations.
They have determined that the operational turbines have not caused significant desensitisation, plot distortion or
plot seduction issues.
RADAR SETTINGS
A number of radar settings will influence both the detection of turbines and the frequency with which they might
generate clutter; unwanted displayed returns. The factors influencing this are:
• The visibility and radar cross section of the turbines*
• The yaw angle of the turbines
• The physical tilt of the radar
• Radar beam switching range
• CFAR settings, weather settings
• STC (Sensitivity Time Control)
• MTD/MTI filter settings
• Channel selection
Some settings are internal, set-up during commissioning and not available to controllers as a live variable.
* Note that the proposed turbine is both visible to the Cornwall radar and with sufficient cross section to be
detectable.
FALSE TRACK GENERATION (FALSE ALARM RATES)
The processing in modern radars can prevent a single turbine from generating false plots and false tracks, broadly
described as radar clutter. By observation this is the case for the existing primary radar installed at Cornwall
Airport. Any future radar will be at least as capable of turbine clutter suppression.
Multiple Turbines
False track initiation both occurs more frequently and is sustained for longer periods where the radar can see a
large cluster of turbines. This has been observed by Air Traffic Control at the airport, on occasion, at the Carland
Cross Wind Farm. It is also greatly reduced where turbines are separated further, acting as individual
02/09/2020 Page 6 of 8Longstone – Cornwall Airport Impact Review Version 1.1 developments rather than a wind farm. This is because the tracking algorithms within the radar processing, will not associate returns that are not consistent with an aircraft. A track will be initiated and displayed if the radar typically sees 3 returns from the previous 5 scans; these from a combination of returns from two or more turbines. Some radars also compare return amplitude to remove ‘angels’ acting as an additional filter to remove irregular returns such as generated by wind turbines. Once a track is initiated the processor will store direction and speed. It will then look for the next associated return within a window related to that speed and direction, allowing pre-determined flexibility on speed and direction changes. All the filters and track initiation algorithms will act to reduce the incidence of false track generation, because that is their purpose. As a result of the observed MTD filtering, requiring more than 1 turbine to generate a false track, there is a maximum separation between adjacent turbines that will allow false track generation. Note that track initiation algorithms will act to reduce the search window for returns to generate new tracks. The track initiation parameters of the Cornwall Airport PSR are not known, therefore the worst case turbine separation to avoid track generation completely is also not know. In practice, where two or three turbines are close enough to enable clutter generation, it would be likely to happen infrequently and when the wind is in certain directions. Where a track is initiated it is unlikely to be sustained for more than a couple of scans as the returns from the small number of well separated turbines, especially if not in a straight or nearly straight line, will not replicate a potential aircraft track. Because of the complexities of the radar detection and processing functions, it is not possible to reliably determine the frequency with which false plots would be generated in a given situation. The best means of estimating this is by reference to the real impacts of operating turbines visible to the radar. Carland Cross is not comparable with more modern developments, having 10 turbines at small separation distances of circa 330m. The proposed turbine would not replicate the false tracks generated by Carland Cross. Carland Cross Wind Farm Layout 02/09/2020 Page 7 of 8
Longstone – Cornwall Airport Impact Review Version 1.1 CONCLUSIONS This review has examined the impacts of the Clean Earth Energy proposed Longstone turbine. The scope was based on extensive discussions with the airport, focusing on the three key concerns identified by Cornwall Airport Newquay; namely the infringement of the Obstacle Limitation Surfaces (OLS), the generation of false tracks on the primary radar and exacerbation of the existing airspace management issues affecting IFR traffic on final approach to runway 30. This report covers the first two points with airspace management covered by a separate report conducted by Cyrrus. The OLS assessment determined that the proposed turbine did penetrate both the Outer Horizontal Surface and the Approach Surface for runway 30. The existing obstacles exceed the height of the proposed turbine and remain the dominant obstacles in the area; thus the proposed turbine does not change the local minimum altitude of approaching or transiting aircraft and as a consequence has no operational impacts. The radar impact assessment determined that the proposed turbine would be detectable. As an individual turbine development, there is very little scope for the generation of false primary radar tracks. It has been agreed with the airport that a radar assessment is required before any additional turbine applications, subsequent to this one. In the event that the turbine is constructed, the introduction of new obstacles should be promulgated in the usual way. The airport will need to consider the need for lighting the turbine. 02/09/2020 Page 8 of 8
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