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Proposed Rule

Marking Meteorological Evaluation Towers

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Federal Aviation Administration (FAA), DOT.


Proposed revision to Advisory Circular; request for comments.


The FAA is considering revising its current Advisory Circular on Obstruction Marking and Lighting to include guidance for Meteorological Evaluation Towers (METs). These towers are erected in remote and rural areas, often are less than 200 feet above ground level (AGL), and fall outside of FAA regulations governing tall structures and their impact on navigable airspace. The proposed marking guidance would enhance the conspicuity of the towers and address the safety related concerns of low level agricultural operations. The FAA seeks comment on the proposed guidance.


Comments must be received on or before February 4, 2011.


You may send comments identified by docket number FAA 2010-1326 using any of the following methods:

  • Federal eRulemaking Portal: Go to and follow the online instructions for sending your comments electronically.
  • Mail: Send Comments to Docket Operations, M-30; U.S. Department of Transportation, 1200 New Jersey Avenue, SE., West Building Ground Floor, Room W12-140, West Building Ground Floor, Washington, DC 20590-0001.
  • Hand Delivery: Take comments to Docket Operations in Room W12-140 of the West Building Ground Floor at 1200 New Jersey Avenue, SE., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.
  • Fax: (202) 493-2251.
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Sheri Edgett-Barron, Obstruction Evaluation Services, Air Traffic Organization, AJV-15, Federal Aviation Administration, 800 Independence Avenue, SW., Washington, DC 20591; telephone: (202) 267-8783; e-mail:

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14 CFR Part 77

Title 49 of the United States Code (U.S.C.), section 40103(a)(1), provides that the “United States Government has exclusive sovereignty of airspace of the United States.” Paragraph (b) of this section directs the FAA to “develop plans and policy for the use of the navigable airspace and assign by regulation or order the use of the airspace necessary to ensure the safety of aircraft and the efficient use of the airspace.”

In recognition of the threat tall structures can pose to aviation safety, 49 U.S.C. 44718 directed the FAA to promulgate regulations requiring notice of proposed structures or alterations of existing structures when the notice will promote safety in air commerce and the efficient use and preservation of the navigable airspace and of airport traffic capacity at public-use airports. (14 CFR part 77.) The agency was further directed to study such structures and determine the extent of any adverse impacts on the safe and efficient use of the airspace, facilities or equipment.Start Printed Page 491

Consistent with the above statutory and regulatory framework, the FAA has adopted policy to establish the standards for which the FAA identifies “obstructions” and “hazards” in the navigable airspace in furtherance of its responsibilities to manage the navigable airspace safely and efficiently. See 14 CFR part 77, and FAA Order 7400.2, Procedures for Handling Airspace Matters. The FAA issues a determination advising whether the structure would be a hazard to air navigation. The FAA may condition its determination of no hazard with the structure appropriately being marked and lighted, as specified in the determination. FAA criteria for marking and lighting of tall structures are found in Advisory Circular No. 70/7460-1, Obstruction Marking and Lighting.

Unless within the vicinity of an airport,[1] proponents of new structures or alterations of existing structures must file notice with the FAA for “any construction or alteration of more than 200 feet in height above the ground level at its site.” 14 CFR 77.13(a)(1). Consequently, as the FAA does not study these structures there is no FAA determination that would specify the marking of these structures.


The emphasis to discover sources of renewable energy in the United States has prompted individuals and companies to explore all means of energy generation. Wind energy, converted into electrical energy by wind turbines, is widely pursued as a viable alternative. In order to determine if a site meets requirements to construct a wind turbine or wind farm, companies erect METs. These towers are used to gather wind data necessary for site evaluation and development of wind energy projects. The data generally is gathered over a year to ascertain if the targeted area represents a potential location for the installation of wind turbines.

Requirements to file notice under part 77 generally do not apply to structures at heights lower than 200 feet AGL unless close to an airport environment. Therefore, the FAA does not have a database of MET locations, nor does it conduct an aeronautical study to determine whether the particular structure would be hazardous to aviation. These towers are often installed in remote or rural areas, just under 200 feet above ground level (AGL), usually at 198 feet or less. These structures are portable, erected in a matter of hours, installed with guyed wires and constructed from a galvanized material often making them difficult to see in certain atmospheric conditions.

While the METs described above are not subject to the provisions of part 77 and therefore, the FAA does not conduct aeronautical studies to determine whether these structures are obstructions and adversely impact air navigation, the FAA does acknowledge that these towers under certain conditions may be difficult to see by low-level agricultural flights operating under visual flight rules. The color, portability of these towers, their placement in rural and remote areas, and their ability to be erected quickly are factors that pilots should be aware of when conducting operations in these areas.

The FAA has received complaints and inquiries from agricultural operations in remote or rural areas regarding the safety impacts of these towers on low-level agricultural operations. In addition, representatives from the National Agricultural Aviation Association (NAAA) met with the FAA on November 16, 2010 to discuss safety specific concerns of the aerial application industry. The NAAA suggested safety guidelines and marking and lighting criteria in order to reduce the risks for aerial applications. A copy of the material provided by NAAA has been placed in the docket.

Proposed Guidance

The FAA is considering revising AC No. 70/7460-1, Obstruction Marking and Lighting, to include guidance for the voluntary marking of METs that are less than 200 feet AGL. The FAA recognizes the need to enhance the conspicuity of these METs, particularly for low-level agricultural operations and seeks public comment on the guidance provided below.

The FAA recommends that the towers be painted in accordance to the marking criteria contained in Chapter 3, paragraphs 30-33 of AC No. 70/7460-1. In particular, we reference paragraph 33(d), which discusses alternate bands of aviation orange and white paint for skeletal framework of storage tanks and similar structures, and towers that have cables attached. The FAA also recommends spherical and/or flag markers be used in addition to aviation orange and white paint when additional conspicuity is necessary. Markers should be installed and displayed according to the existing standards contained in Chapter 3, paragraph 34 of AC No. 70/70460-1.

The FAA is also considering recommending high visibility sleeves on the outer guy wires of these METs. While the current Obstruction Marking and Lighting Advisory Circular does not contain such guidance for high visibility sleeves, the FAA specifically seeks comments on this recommendation.

The FAA anticipates that a uniform and consistent scheme for voluntarily marking these METs would enhance safety by making these towers more readily identifiable for agricultural operations.

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Issued in Washington, DC, on December 29, 2010.

Edith V. Parish,

Manager, Airspace, Regulations and ATC Procedures Group.

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1.  14 CFR 77.13(a), paragraphs (2), (3), (4) and (5) are not relevant to this issue.

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[FR Doc. 2010-33310 Filed 1-4-11; 8:45 am]