Wind Turbine Wake Plumes are a Hazard to Aviation Safety

Introduction

December 2009, Australia is the first country to draw Wind Turbine Wake Plume extents to the attention of the aviation community despite both developer's and researcher's awareness of the velocity deficit, and the wake turbulence behind turbines well before this timeframe.

I like to refer to the phenomenon as a Wake Plume because it has both elements of wake tubulence and a plume which tends to be contained, rather than diverging downwind from the turbine.

Around September 2008 I studied Wind Farm Wake Turbulence after I had become aware that Epuron had lodged a development application for the Gullen Range Wind Farm to be situated near the Crookwell Aerodrome, an aerdrome I have used for several training flights, and one which was subjected to my Private Pilot Licence (PPL) flight test.

Crookwell Aerodrome (YCRL) is a 2953' AMSL high elevation airport, comprised of a relatively short 950 metre grass runway that is shielded by a ridge on the western side, which makes takeoffs to the west from runway 27 challenging, and these features make it an interesting training strip for Private and Commerical licences. It is known that at least one Authorised Testing Officer (ATO) uses the strip for the Commercial Pilot Flight Test, and several ATO's have used it for PPL flight tests, and this aerodrome is also very important to the local Crookwell area when it is used for fire fighting operations.

I forwarded my initial findings on Wake Plumes between the 5 and 8 Sep 2008 to the Upper Lachlan Shire Council, NSW Planning, and to the Civil Aviation Safety Authority (CASA), with the view to have the Wake Plumes taken into consideration when reviewing the development application. I subsequently sent them again to the Crookwell Upper Lachlan Shire Council on the 21 Sep 2008.

The Lachlan Upper Shire Council, and NSW Planning authorities sought information from various aviation experts and authorities, but since Crookwell Aerodrome was an Authorised Landing Area (ALA) the official CASA response was Crookwell Airstrip is not covered under CASA's legal jurisdiction and thus has no comments to provide regarding the proposal. This response is a direct citation taken from page 16 of the Director Generals Assessment.

The development was subsequently approved by the NSW Minister for Planning with conditions of approval that included the rejection of 11 wind turbines in order to preserve the aerodrome. Another condition was that lighting is NOT to be installed, other than low intensity lighting, and that the proponent is to engage with CASA to determine the extent of hazard lighting. The conditions also included the removal of the plus or minus 250 metres turbine placement variation from the development application.

The aforementioned approval was granted in the time-frane before three NSW Environment and Planning court hearings could be heard, citing that the development was a Major Project under section 75B(1)(a) of the Environment Planning and Assessment Act 1979.

CASA AC 139-18(0) Obstacle Marking and Lighting for Wind Farms was subsequently withdrawm, and several wind farms now have the priviledge of silent running with no obstacle lighting for pilots at night, despite turbine blade tips being in excess of 110m above the ground level.

To date more than a year later, there has been no national aviation authority undergoing studies of the Wake Plume phenomenon. However, CASA informed me on the 7 Dec 2009 that they are now studying it and proposing to draft some legislation that will be available for public comment. This is a first for Australia, and indeed the World Wide Aviation community, and I believe I would not have become aware of the phenomenon had the wind farm development near Crookwell Aerodrome Australia been situated further from the aerodrome and gone unnoticed.

CASA also lists Project AS 06/07 Assessment of obstacles including wind turbines and exhaust plumes, dated 19 Jul 2006, which was recently renamed and is based on CASR Manual of Standards Part 139 - Aerodromes, and CASR Part 173 - Airspace, neither of which afford any protection against turbines unless they are proposed in close proximity to a registered or certified aerodrome and have appropriately operating airspace. At the time of writing (Dec 2009), this legislation has no regard for Wind Turbine Wake Plume, although it has mention of vertical plumes from chimneys. CASA has been working on this project since 2006.

What I believe is that we need legislation that can be used irrespective of the registration status of the aerodromes and irrespective of where a turbine is located, and that legislation needs to be enforceable against a developer, and not necessarily leaving the onus on a pilot or an aerdrome operator.

If you are aware of other runways affected by the threat of wind power generating turbines I would be interested to help. I have appeared as a witness in the NSW Environment and Planning Court to contest the placement of turbines under the potential threat of Aviation Safety represented by these Wake Plumes. I believe the protection can be afforded to the aerodrome operations under due dilligence and duty of care, despite the present lack of the Aviation legal framework, which CASA have recently informed me, it is now in the process of rectfying.

Ralph Holland 2008-2009 - you may contact the author at:

Gullen Range Wind Farm - Crookwell

My first defence of the Crookwell Aerodrome was back in Sep 2008 when I summarised some research Turbine Wake Plume and analysed the Epuron Gullen Range - Aviation Hazard Report and criticised it on 11 counts which you can find here in Generic Circuit and forwarded to the planning authorities for their consideration.

I did not realise just how significant these Wake Plumes were in strength and extent when I initially forwarded the papers.

Under increasing awareness brought about by investigations and reports that were submitted to the NSW Environment and Planning Court, I became aware that the Wake Plume extended much further than my original searches had found. I searched for more research papers and was suprised. The data showed that the Wake Plumes do not diverge as people would expect, and that they could extend several kilometres downwind from the turbines, further the plume starts out largely contained by the blade disk behind the turbine and eventually becomes bound between the ground and outer-extremeties of the blade disk, i.e. the plume fills in behind the turbine and the ground and continues downwind for some distance..

This later realisation can be found in my presentation material, which was presented as part of my evidence in the NSW Environment and Planning court. This was an open process, with the proponent, the court and CASA receiving ALL my submissions and then followed by a hearing in court.

I also, just a few months earlier, had the opportunity to fly-by the Cullerin Wind Farm and video Windmills in the Mist while the turbine blades where just protruding above the cloud. This was originally to show the danger of white blades just protruding from white clouds, and to my suprise and delight, I could see down to the ground in streams behind the turbines. This was confirmation that I was on the right track with my investigations into the effects of these wake plumes extending downwind from power generating turbines.

At about this time I fully disclosed the extent to CASA, and forwarded the video evidence and presentation, which was just before I found that the Wake Plumes could extend even further. I performed some more searching after I received the joint expert witness aviation report from the NSW Environment and Planning just before the court proceedings and I found that the plumes can extend more than 15 kilometres over the ideal surface of the ocean. Evidenced in the Syntehtic Aperture Radar (SAR) data obtained from measurements of wind velocities around the Horne Rev offshore windfarm near Denmark. This is not insignificant when you understand just what comprises these Wake Plumes.

My presentation material is in two parts, the first summaries several researcher's measured data, while the second presents a need for a buffer zone around the turbines to prevent their placement interfering with aircraft. This material was presented to court for consideration, and it is a difficult subject since there was currently no national avaiation authority studying the phenomenon, and no aviation legal framework to protect the unregistered Crookwell Aerodrome. My presentation was, however, based on Aviation Safety and appealed to the common law processes of due-dilligence and duty-of-care of the state planners.

The proposed turbine locations near Crookwell Areodrome, can been seen in Google Earth data which I derived from the Gullen Coordinates. I have only included the Northern cluster, and some of the Southern Cluster, because it tooks hours to form this data and I lost time before the court hearing, as well as interest in the remaining turbines because of the extent of the distances in my study. I included the last of which were swept by the buffer zone, and the first of which were completely anhialated. The whole preparation of which was onerous, and performed at my expense, at the expense of several days of the work I do for my living, some sleepless hours, and at times when there was no clear resolution in sight. I am glad that I managed to perservere - there is nothing like an enthusiast doing something they believe is right - for they tend never to give-up. My wife will confirm that I am obsessive - and I believe that personality trait (or defect) assisted in this case.

I was mainly concerned with the turbines in close proximity of the aerodrome, and those that would be intercepted by the CAT-B aircraft circling area, as well as those that later fell within the 15 kilometre buffer zone.

The 15 kilometre buffer was a late submission derived from SAR data for offshore wind farms, where the Wake Plume is propagating over the perfect boundary represented by the sea. I suspect that the wake propagation distance would be less over land, and particularly land with the surface roughness, and with trees etc, as found in the Crookwell area. Because of this uncertaintly I actually called for a scientific study of the Wake Plume, velocity deficit, turbulence and extent by physical measurement of exising wind farms in the area, as well as using scale models in a wind-tunnel taking local terrain roughness into account in my dispositions to the court, and I still believe such a study should be commissioned.

It is my belief that the Wake Plume represents a Safety Hazard to Aviation, in that in parts it represents a void to flight, and in other parts represents a wind-sheer, velocity deficit, and turbulence. I believe that the Wake Plume may result in accidents if pilots happen to fly into it, or across it, and it is with this basis of reasoning that I have been petitioning CASA and intend to pertition ICAO to raise awareness of the dangers. I also have supporting evidence provided by Richard Thompson's personal account of flying into, and luckily out of, such a turbine Wake Plume.

In my opinion, the rejected 11 turbines are not enough, because there are still several turbines within the CAT-B circling area, and no real allowance has been made for a buffer from these, and other, turbines. There is no buffer protection against the Wake Plumes, as can be seen in the following image, and I am dissappointed that this has caught the aviation community off guard, and that the appropriate authorities have not been able to take the full extent of the Wake Plume into account - Ralph Holland 13 Dec 2009.

Legislation and No Fly Zones

I believe that a buffer zone is required around a power generating Wind Turbine to isolate aircraft and pilots from the affects of the Turbine Wake Plumes. Experimental evidence shows that the Wake Plume extends several kilometres downwind from the turbines, and other research shows that the Velocity Deficit effect is strengthened behind Wind Turbine clusters. In my opinion, the remaining turbines will present their Wake Plume towards the Crookwell Aerodrome under South-Westerly wind conditions.

CASA has indicated that it is studying and proposing to draft legislation and instrumentation for these obstructions, and it is probable that such legislation will determine safe and reasonable distances, which may lead to the imposition of Restricted or Danger Areas - no fly zones - around wind turbines.

With the remaining turbines still relatively close to Crookwell Aerodrome, the aerodrome is still under threat of closure. Subsequent CASA legislation runs the risk of closing the aerodrome after the Wind Farm development approval process is completed.

It is also probable that the requirements for markings and lighting will be more inline with the European standards of orange or red striped-blades and nacelle obstacle lights. Again it is probable that this legislation will be drafted after the development approval resulting in yet another unsafe situation, as we have with the Lake George Capital Wind Farm turbines that are unlit, with their blades too poking out of clouds.

These turbine hazard findings will be required to be promulgated through pilot education schemes to reinforce that Wind Turbines and Wake Plumes are to be avoided, and I await the new CASA legislation and monitor their projects, but it may be too late for Crookwell Aerodrome.