Offshore Wind Farm Helicopter Search and Rescue Trials 8 Report of the Officer Commanding C Flight, 22 Squadron
( Comment by Colin Brown) Offshore Wind Farm Helicopter Search and Rescue Trials INTRODUCTION 1. On 22 Mar 05 an informal trial examining Sea King HAR.3 radar performance in relation to offshore wind farms was carried out on behalf of the MCA. The MSS-modified aircraft carried out the trial at the North Hoyle wind farm, which is situated approx 5nm NNW of Rhylf. North Hoyle (fig 1) contains 30 turbines in a regular grid of 6 rows and 5 columns, with the rows orientated approx ENE / WSW. The rows and columns are spaced approx 300m and 700m apart respectively. 2. Weather conditions for the trial were broken medium-level cloud, nil precipitation, wind southerly at 20 kts and sea state 3. Although a small fishing vessel had been chartered for use as a target, its arrival at the wind farm was delayed; fortuitously, the wind farm workboat (‘Celtic Wind’, similar in size to a Mersey-class lifeboat) was present and was used as a target for the majority of the trial. The aircraft operating crew was a standard SAR crew with no formal trials experience. Fig 1 – North Hoyle Offshore Windfarm RESULTS 3. Sea King Radar Performance. Side lobe returns were found to extend approximately 100m to either side of each turbine, with the sidelobe depth estimated at less than 50m. The target, which was moving between the turbines within the wind farm, was tracked from the aircraft positioned in the 50 ft hover between 0.25 and 0.5 nm clear of the sides of the wind farm. These results are consistent with those found during the MCA / QinetiQ trials of July and August 2004 ( ref. 1) and would be expected with respect to the Sea King’s comparatively wide horizontal beam width. See also figure 28 4. The target could be tracked to a distance of approximately 100m from each turbine. Beyond this point the target could be recognised at a slightly closer range to the turbine, but only if it had been previously identified at a greater separation and radar processing continuously adjusted. In summary, the minimum radar detection range from a turbine is estimated to be 100m. Possession of a chart of the wind farm layout is considered to be extremely desirable to allow the radar operator to accurately interpret radar returns. As with marine radar systems, detection of vessels close to turbines, ie. at distances less than 100m, is difficult even at short range. Large scale plans of wind farm layouts will be necessary for all emergency service activities as will the short range marking and lighting of individual turbines 5. Thermal Imager Performance. The RAF Sea King is equipped with an externally-mounted FLIR Systems Inc STAR-Q infra-red and TV camera assembly. As the infra-red camera cannot ‘see’ through airborne moisture, it would be of verylimited use in fog, drizzle or rain. It would, however, perform well in haze (dry airborne particulates). The target vessel was easily located within the wind farm complex, and workmen on turbine ladders and work platforms were clearly identified at a range of approximately 1 nm. See figures 17 to 21. In restricted visibility, and in the absence of voice communications where casualties might report positions within the marked turbines configuration, radar would be the major means of casualty detection 6. Homer Performance. The Sea King radio homer system utilises the lateral displacement of a vertical bar on an instrument to indicate the sense of a target relative to the aircraft heading (ie left, right or directly ahead / astern). A ‘spoking’ direction indicator is not fitted. With both the aircraft and the target vessel inside the wind farm, at a range of approximately 1 nm, the homer system performed accurately on FM Ch 67 with no apparent degradation. In the previous trials, RNLI lifeboat VHF Direction Finding equipment had been found to operate satisfactorily within the wind farm, except when very close [<50m] from turbines 7. VHF FM Radio Performance. Radio checks were carried out in the 50 ft hover on FM Ch 0 to both Holyhead and Liverpool Coastguards, with the aircraft laterally displaced from the wind farm by approximately 0.3 nm. The aircraft was positioned to place the entire wind farm complex between the aircraft and the relevant land-based aerial. (Checks were carried out to Holyhead CG from east of turbine 25, and to Liverpool from west of turbine 16.) Comms were very clear in bothcases, with no apparent degradation of performance. Communications with the MCA operators on board “ Lady Gwen ll” were also fully satisfactory 8. Compass Performance. With the aircraft situated inside the wind farm, no deviation was apparent on any compass system. 9. Aircraft Power Requirement. The power requirement rose from approximately 70% matched torques when hovering at 50 ft in clear air to just below 80% matched torques when hovering at 50 ft in the lee of the wind farm, at approximately 0.3 nm from the turbines. No noticeable increase in turbulence was encountered. See reference 2 and also reference 3 10. At North Hoyle, the turbine blades cannot be remotely braked. Instead, they can be remotely feathered, then manually locked in an upright-Y configuration from within the ‘pod’ at the top of the upright shaft to allow helicopter winching acces. IF however, the blades are feathered but not manually locked, they may still rotate slowly (as was observed during the trial). Unless the blades can be confirmed as having been manually locked, therefore, helicopter rescue from a wind turbine would be extremely, if not prohibitively, hazardous. See Fig 22 illustrating the configuration required for an MCA compliant active safety management system. Annex 4 of MCA’s MGN 2754 explains these and is attached to this report as an Annex SURFACE RESCUE WITHIN A WINDFARM 11. Visual Conditions. In good visibility, a helicopter could be safely flown into a regularly-spaced wind farm complex. Rescue from the surface could obviously only be carried out, however, if the target was sufficiently clear of the turbines for the rotating blades not to pose a hazard. The pilot’s judgement would be the deciding factor in this issue, although it is considered that a helicopter could not safely be positioned laterally from the turbine within a range equal to the span of the turbine blades Launching a surface rescue vessel in all cases would be appropriate. See comment following the next section 12. Fog. While a Sea King could be safely (albeit slowly) navigated down the wider lanes at North Hoyle in poor visibility under internal radar control, in order to effect a surface rescue the radar operator must leave the radar console to operate the rescue hoist. In conditions of poor visibility this situation would result in the helicopter crew being unable to maintain a safe separation from the turbines. In foggy conditions, therefore, a helicopter would not be able to safely effect a surface rescue within a wind farm and would best be employed as a radar search platform outside the wind farm. Surface vessels should be used to effect a rescue in fog. Offshore wind farms, particularly the proposed Round 2 sites, can be a considerable distance offshore. Therefore passage times for surface craft may be a significant factor. Figures 13 and 14 respectively indicate the positions the proposed wind farm sites and the position of RNLI stations with the types of lifeboat stationed at each 13. Radar Searching. While it would be possible for the helicopter radar operator to verbally direct a rescue vessel onto the target, the most efficient method would seem to be to relate the target’s position to a specific turbine and allow the surface vessel to proceed to that location, eg ‘300m south of turbine 18’. Clearly, this would require the radar operator to have a reference copy of the wind farm plan. Interpretation of an extensive and irregularly-spaced wind farm complex would be extremely challenging, even with an accurate plan available. Turbines which are irregularly spaced, either by design to reduce visual seascape effect from ashore [ see figure 28 ] or because of geological problems during installation, would cause the above search method to be difficult Original Signed J M STANLEY Squadron Leader Officer Commanding Distribution:
2 Research initiatives for improving the safety of offshore helicopter operations” BMT Fluid 3 Mechanics and CAA, 2004 3 The Effect of Wind Turbine Wakes on Wind-Driven Craft” by: CD Ziesler, 2001 4 Marine Guidance Note 275 (M) Proposed UK Offshore Renewable Energy Installations - Guidance on Navigational Safety Issues” MCA July 2004 |
