Date of submission : 20 – 11 – 2011 . Day of submission : Sunday . Grade : 11 .

1. Physics Project ( Term 1 ) Impact of wind on navigation • Date of submission : 20 – 11 – 2011 . • Day of submission : Sunday . • Grade : 11 . • Section : 51 . • Group names : • Maitha Ali . • Salha Salem . • Rafeea Ali . 1

2. Potential effect of wind turbines on navigational systems • Introduction : • The Working Group for Wind Energy, Defence and Civil Aviation Interests has to date focused on the impact of wind turbines on radar. However, at the meeting held on 12 Sep 01, it was suggested that consideration be given to assessing the impact on aeronautical navigation aids . • Although significant work has been undertaken to establish the effects of wind turbines on radar, no work has been specifically commissioned in respect of the potential effects on aeronautical navigation aids. However, due to uncertainty concerning the issues, it was agreed that the CAA would develop a paper to identify areas where additional work may be needed to determine both the effects and the restrictions necessary to achieve an acceptable level of safeguarding. 2

3. Aim: • The aim of this project information is to review those aeronautical navigation systems that may be degraded by the effects of wind turbines but require further investigation of the effects to determine appropriate protection. This project does not attempt to be a technical examination but is merely an assessment of the situation against which further technical work can be planned. 3

4. Background: • It is recognized that wind turbines do not transmit or radiate other than the generation of background noise similar to any non-transmitting electrical device. However, the physical characteristics of a wind farm and its operation are known to have an effect on the performance of primary radar. In respect of navigational aids, the impact on performance is potentially less obvious but could be of a similar nature. In essence, the siting of wind turbines in close proximity to a navigation aid may result in an effect on the coverage of the radiated Signals. 4

5. The particular aids of interest, which employ ground based components, are: - Non-Directional Beacons (NDB) . - Distance Measuring Equipment (DME) . - Instrument Landing System (ILS) . - MicrowaveLanding System (MLS) - VHF Omni-directional Radio Range (VOR) - TACAN • In addition, satellite based navigation systems (GPS) and airborne radars (e.g. Airborne Early Warning (AEW)) need to be considered. In addition, there are specific MOD issues that may affect aviation generally in terms of the effects on Terrain Following Radar (TFR). 5

6. Potential Impact of Wind Turbines: • As already stated, wind turbines do not emit RF transmissions but, through the nature of their physical characteristics, have the potential to affect the operating characteristics and performance of aviation surveillance and navigation systems. This has already been clearly identified in the case of primary radar. This is likely to occur if the turbines are located in a position that could affect the radiated signal pattern from a particular aid. • Each navigation aid has an associated area of Designated OperationalCoverage (DOC), which is the volume of airspace (e.g. a circle 25 nm radius, sea level to 10000 ft) in which the service is protected. Within this volume, the aim is to ensure that the aircraft using the navigation aid can rely on the continuity and integrity necessary to meet the approved standards of use. 6

7. Therefore, it would be possible to determine the likelihood of performance degradation by simply considering the proposed siting of wind turbines versus the DOC of a particular navigation aid. However, given the propagation characteristics of antennas, it is possible that the siting of a wind turbine adjacent to, but not infringing, a DOC, may cause an effect on the radiated signal characteristics which affects performance within the DOC. • In considering the potential effects and ensuring that an Air Traffic Service(ATS) provider can take the appropriate measures to satisfy safety requirements, it is necessary to consider the current notification process and availability of information. Within the Site Safeguarding process, proposed wind turbine developments within a 30 km radius of an airport or area radar/navigation aid will be notified to the appropriate ATS provider. 7

8. Taking into account the proposed location, terrain screening and physical characteristics of the turbine, coupled with antenna patterns and DOC information appropriate to the navigation aid concerned, it would be possible for the ATS provider to determine whether or not a valid objection to the proposal existed. However, given the variable factors, it is necessary to review each proposal on a case-by-case basis. 8

9. Although the factors described above would appear to meet the majority of situations concerning navigation aids listed at para 5, the situation is not so clear in the case of precision approach aids. ILS and MLS provide a means by which aircraft can, to a high degree of accuracy, position themselves for an approach to a runway in low visibility conditions. These systems are required to perform to high standards of accuracy and integrity within a very critical stage of flight. Furthermore, within the DOC, these systems are very sensitive to physical effects, which can result in degradation of performance. In this respect, there is a likelihood that wind turbine effects could be harder to define, thereby making it difficult for service providers to determine whether or not there is a potential impact on aviation. • In addition to the more traditional navigation aids detailed above, there is a need to briefly consider GPS and the airborne radars. 9

10. GPS is unlikely to be affected by wind turbine developments unless physical obscuration occurred. As this would occur only if the turbines were between the GPS receiver on an aircraft and the satellite constellation, this is not considered to be a realistic issue of concern from an aviation perspective. • Turning to airborne radars (e.g. AEW, TFR, Weather radars etc), the effects will be similar to those experienced by ground based primary radars. However, they will be transitory and have to be treated in the same way as any other physical response detected by a mobile platform. Nevertheless, there is potentially a more complex issue in respect of TFR equipped military aircraft. The physical size of wind turbines is such that they create a physical obstruction in low-flying training areas. Therefore, their detection on radar, or their effect on TFR performance, becomes a more critical issue. 10

11. Furthermore, having been detected, does this in itself have a causal effect that creates a further affect between military aircraft and other operators. However, there may be other issues outside of affecting TFR performance that may also need to be addressed. These include charting, impact on adjacent traffic, use of Collision Warning Systems etc. 11

12. Conclusion: • Having considered the potential effects on aeronautical systems other than primary radar, it is concluded that: - Wind turbines may cause an effect on the performance of a ground based navigation aid within its DOC. However, the extent of this will have to be assessed on a case-by-case basis. - The current notification process will enable ATS providers to make a valid assessment of each wind turbine proposal in relation to the performance and technical characteristics of navigation aids. - There is a concern that the effects on precision approach aids such as ILS and MLS are harder to define and that a study of the potential effects to define the necessary protection requirements would assist both service providers and the renewable energy industry, 12

13. - It is considered to be highly unlikely that there would be an adverse effect of GPS operations. • Although there is an effect for airborne radar platforms such as AEW, there is no apparent requirement for further studies. However, there is valid MOD concern in respect of effects of TFR that should be further assessed in order to quantify the exact implications. From this, the need for detailed investigations can be determined. - It should be noted that the CAA will monitor occurrence reports and will, should it be deemed necessary, request further work to be carried out if there is evidence that suggests wind turbine developments may be the cause of any degradation in performance of aeronautical safety of life systems. 13

14. Recommendations: • It is recommended that: - A study is initiated to determine the possible effects of wind turbine developments on precision approach aids and to recommend the necessary protection criteria. - An assessment is undertaken of the potential effects of wind turbine developments on TFR performance and the consequential impact on low-flying training and its interaction with other airspace users. - The CAA continues to monitor occurrence reports and briefs the Working Group for Wind Energy, Defence and Civil Aviation Interests of any occurrences that could require further investigation into the effects of wind turbine development. 14