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June 1, 2015 In News

Flash Experts Parse North American Obstruction Lighting

Editors of North American Windpower asked Flash Technology to provide technical expertise regarding the current state of North American obstruction lighting, including standards and lighting regulations. Flash provided the following insights.

Navigating North American Obstruction Lighting Standards

Aviation obstruction lights have been seen on tall structures since the 1930s with the advent of nighttime flights. In the 1990s came cell phone towers, and more recently, wind turbines have become a common sight on the North American landscape. All of these obstacles are considered intrusions to navigable airspace and require a means of warning to approaching pilots of the inherent danger of the obstruction.
Aviation obstruction lights have been seen on tall structures since the 1930s with the advent of nighttime flights. In the 1990s came cell phone towers, and more recently, wind turbines have become a common sight on the North American landscape. All of these obstacles are considered intrusions to navigable airspace and require a means of warning to approaching pilots of the inherent danger of the obstruction.

At this point, manufacturers and developers of wind farms are familiar with the U.S. standards for marking and lighting turbines, but how do those standards compare with those of Canada and Mexico? There are some similarities contained in their respective regulations, but also some subtle – and not so subtle – differences.

The U.S., Canada and Mexico are all member states of the International Civil Aviation Organization (ICAO). Created in 1944 and headquartered in Montreal, Canada, the ICAO is an agency of the United Nations whose mission is “to achieve its vision of safe, secure and sustainable development of civil aviation through the cooperation of its member states.”

The purpose of the ICAO is to set standards and regulations necessary for aviation safety, security, efficiency and regularity, as well as aviation environmental protection. Because the U.S., Canada and Mexico are all among the ICAO’s 191 member states, it is not surprising to find similarities in wind turbine marking among the three countries, yet each maintains some degree of autonomy in its standards. With wind turbine technology pushing towers and blades to new heights, all three countries have adopted standards specific to wind power plants in recent years.

ICAO

The ICAO regulation dealing with obstructions is Annex 14, Chapter 6 – Visual Aids for Denoting Obstacles. It offers guidelines for the characteristics of different obstruction lights and suggestions regarding how to paint and/or light different structures. In November 2009, wind turbines were finally recognized as something unique in Section 6.4 of Annex 14. Included in the ICAO recommendations for wind turbines are the following:

  • A wind turbine shall be painted and/or lighted if it is determined to be an obstacle;
  • The blades, nacelle and upper two-thirds of the supporting mast shall be painted white; and
  • When lighting is deemed necessary, medium-intensity lights should be used.

In the case of a wind farm, lights should be installed as follows:

  • The perimeter of the wind farm should be identified;
  • The spacing of lights should be in accordance with the recommendations of any other widely spaced obstacles;
  • Flashing lights, when used, should flash simultaneously;
  • The tallest wind turbines should be identified regardless; and
  • Obstacle lights should be installed on the nacelle in such a manner as to provide an unobstructed view for aircraft approaching from any direction.

 

U.S.

In the U.S., aviation safety is regulated by the Federal Aviation Administration (FAA). The FAA was created in 1958 to provide for safe and efficient use of national airspace, and it is the organization that sets the standards for aircraft warning lights. In general, the FAA requires obstructions 200 feet (approximately 61 meters) or higher to be marked (painted) or lit.

It was not very long ago that the FAA did not officially recognize the difference between a wind turbine and any other tall structure. That meant that it was common for every nacelle on a wind farm (as well as adjoining met towers) to be mounted with two flashing beacons day and night. This requirement obviously did not sit well with developers, owners and local communities.

In 2005, the FAA completed a study to determine the most effective and efficient technique for obstruction lighting of wind farms. The results of that study paved the way for changes made to the standards for marking and lighting wind turbines, and in 2007, the FAA published Advisory Circular 70/7460-1K CHG 2, which included the new Chapter 13: Marking and Lighting Wind Turbine Farms.

Among the recommendations specific to wind turbines and wind farms were the following:

  • Not all units within a wind farm need to be lighted. Definition of the periphery of the installation is essential. However, lighting of interior wind turbines is of lesser importance unless they are taller than the peripheral units;
  • Obstruction lights within a group of wind turbines should have unlighted separations or gaps of no more than half of a statute mile if the integrity of the group appearance is to be maintained. This is especially critical if the arrangement of objects is essentially linear;
  • Any array of flashing or pulsed obstruction lighting should be synchronized or flash simultaneously;
  • Nighttime wind turbine obstruction lighting should consist of the preferred FAA L-864 aviation red-colored flashing lights; and
  • Daytime lighting of wind turbine farms is not required, as long as the turbine structures are painted in a bright white color or light off-white color most often found on wind turbines.

 

There are some similarities contained in obstruction lighting for North American countries but also some differences.

 

Canada

In Canada, airspace is controlled by Transport Canada. Similar to the FAA’s Advisory Circulars, Transport Canada publishes Canadian Aviation Regulations (CARs), and the one that mandates obstacle marking is CAR Standard 621: Obstruction Marking and Lighting.

Just like the FAA had to make some adjustments in its standards as wind farms became more prominent, Transport Canada published an updated CAR 621 in December 2011 containing a new chapter entitled Chapter 12 Wind Turbines and Wind Farms.

The recommendations are very similar to the FAA and ICAO recommendations for marking and lighting wind turbines:

  • For the purpose of “day protection,” wind turbines of a wind farm are painted a white or an off-white color;
  • A wind turbine is lighted with a CL-864 medium-intensity red flashing beacon for nighttime hours;
  • A group of wind turbines is indicated to pilots by installation of CL-864 medium-intensity red flashing beacons on specified wind turbines on the perimeter of the wind farm;
  • The lights are located so as to define the wind farm and spaced at a horizontal distance in the order of 900 meters for given directions of aircraft approach;
  • In addition to the perimeter lights, the dominant (highest in absolute height) wind turbine within the wind farm is also required to be lighted; and
  • All indicator lighting provided for a wind farm flashes simultaneously.

 

Mexico

Mexican airspace falls under the jurisdiction of the Direccion General de Aeronáutica Civil (DGAC), and its standards are published in Circulares Obligatoria. For obstruction lighting, the Circular Obligatoria is DA-04/07 R-1, and its most recent version came out in April 2012 with a chapter dedicated specifically to wind turbines. Although there are some similarities, the Mexican regulation is decidedly different from the ICAO, FAA and Transport Canada standards.

The Mexican standard is similar to marking for lattice towers and requires daytime marking beyond the white paint recommended by the other authorities. It allows for two ways to warn pilots of a wind turbine invading the airspace in daylight hours: bands of orange paint over the standard white or off-white paint or a medium-intensity white flashing beacon (ICAO Type A/FAA L-865). If paint is desired, the paint scheme involves both the support structure and the blades. The support structure requires one two-meter-wide band of aviation orange paint at one-third of the height from the ground level and another painted beneath the nacelle at a distance of one-third the length of the blades. On the blades, the DGAC requires three horizontal stripes of equal width on the last third of the blade tip, starting with aviation orange on the inside, a white stripe in the middle and a final orange stripe.

If paint is not desired, a medium-intensity dual lighting system may be employed, consisting of a medium-intensity white flashing beacon in the day (ICAO Type A/FAA L-865) and switching to a medium-intensity red flashing beacon at night (ICAO Type B/FAA L-864). Like the U.S., Canada and ICAO specifications, the DGAC suggests that if there is a group of turbines in the same location, lighting and marking may be limited to every 900 meters.

It must be noted that all four of the regulations (ICAO, FAA, Transport Canada and DGAC) are guidelines, and the local civil aviation authorities must conduct an aeronautical study before any turbines or towers are installed. The local authority may require more or less stringent marking or lighting depending upon local air traffic, as well as proximity to an airport or flight path and neighboring residences.