Meteorological Evaluation Towers (MET) are placed in remote locations to gather wind resource data for one or two years. These MET towers vary in height from 60 to 100m (197 to 328 ft) above ground level (AGL) and are getting taller to provide the best wind data. Typically, towers under 200-ft AGL require no marking or lighting. This changed with an agricultural pilot’s fatal collision with an unmarked MET tower in January 2011. The National Agricultural Aviation Association helped with suggestions and comments to improve the safety of low flying agricultural operations.
The LEDBEACON3 from TWR Lighting is one product of LED light developments. It consumes less than 6W. The company also provides remote monitoring equipment for several MET towers with the DM900 Wireless Remote.
The FAA provides guidance for the voluntary marking of MET towers erected in remote and rural areas that are less than 200-ft AGL. This guidance will enhance the towers’ visibility for low-level agricultural operations. First, if towers are not going to be lit for visability during both day and night then they should be painted in alternating bands of aviation orange and white paint in equal width with bands at the top and bottom ends colored orange for daytime marking. Second, towers should have high visibly sleeves installed on the outer guy wires for daytime marking. Third, towers should have high visibly orange spherical marker balls attached to the guy wires for daytime marking. Fourth, they will be lit with an appropriate FAA approved lighting system for nighttime marking. The FAA intends, at a future date, to amend the advisory circular AC70-7460-1K to include guidance on sleeves.
The FAA requires a sponsor to submit FAA Form 7460-1 for all structures over 200 ft. The FAA then reviews the location, height, and hazard to aviation, and provides its determination along with their marking and lighting recommendation.
It’s not hard to see how unmarked MET tower could blend into background haze. Towers less than 200 ft once required no marking or lighting. This changed with an agricultural pilot’s fatal collision with an unmarked MET tower in January 2011.
The Advisory Circular AC70-7460 provides guidelines for marking and lighting structures for daytime and nighttime hours. Painting the structure as discussed or using a white medium intensity (MI) flashing light increases daytime conspicuity. Red or white MI flashing systems provide nighttime visibility. However, a white flashing light (L-865) at night is not community friendly.
MET towers from 200 to 350-ft AGL require a red MI obstruction lighting composed of one flashing omnidirectional beacon (L-864) at the top of the structure and two or more steady burning (L-810) lights at the intermediate level for nighttime conspicuity.
MET towers from 351 to 500-ft AGL require a red MI obstruction lighting composed of one flashing omnidirectional beacon (L-864) at the top of structure, two flashing omnidirectional beacons (L864’s) at the mid-level, and three steady burning (L-810) lights at the one-quarter and three-quarter levels for nighttime conspicuity.
These lighting systems must be monitored every 24-hours by visual or automatic means. It is extremely important to visually inspect obstruction lighting in all operating intensities at least once daily. When using remote monitoring devices, the communication status and operational status of the system should be confirmed at least once daily. For each structure, a daily log should be maintained to record the lighting system’s status.
A few companies like ours offer an optional monitoring service that includes filing the FAA Notice to Airman (Notam) with Flight Service Station (FSS), notifying particular company personnel of site issues by email, phone call, or fax, along with removal of Notam after resolving a site issue, and monthly electronic site reports.
Wind turbines are fairly obvious but MET towers are less visible. TWR’s Lighting & Solar Systems meet the requirements of FAA’s Engineering Brief # 76, which requires seven days of autonomy. The company also provides wire sleeves and marker balls to provide complete MET tower marking and lighting.
The major challenge in lighting MET towers has been the unavailability of local utility power in areas where utility-scale wind farms are planned. Therefore, the towers need power from a temporary source.
Previous generations of obstruction lighting have used incandescent lamps, strobe tubes, and quartz halogen lamps as light sources which are neither energy efficient nor practical for use with solar power. Thanks to advancements in light-emitting diodes (LED), the industry can replace the power-hungry light sources with LEDs, which consume considerably less. One result is the MI L864 LED Beacon (LEDBEACON3) that consumes less than 6W. This system still meets or exceeds all photometric requirements of 2,000 Candela red-light output.
LEDs also allow economically powering obstruction lights with solar panels. This temporary power source has become a preferred choice with several companies providing wind assessment. The setup consists of batteries to power the lights and solar panels to charge the batteries.
TWR Lighting has developed an MI Red LED Lighting System operating on 24 Vdc, the lowest power consumption available. A light kit (part number LK1A1MET24VDC) consumes only 142W over a 24 hour operating period. This power consumption is about 25% of what our 120-Vac MI System consumes.
The 24-Vdc lights can be powered by a 175-W solar panel across all U.S. regions. The company has partnered with a solar-panel supplier to provide an MI lighting setup with solar panels for less than $10,000 per installation. WPE
By: James Syzdek, Director of Business Developmen-Wind Energy, TWR Lighting Inc., Orga Aviation Lighting Inc.
Filed Under: Obstruction lighting, Safety, Towers
