[Federal Register Volume 76, Number 122 (Friday, June 24, 2011)]
[Rules and Regulations]
[Pages 36983-36986]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2011-15746]



Federal Aviation Administration

14 CFR Part 77

[Docket No: FAA 2010-1326]

Marking Meteorological Evaluation Towers

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Policy statement.


SUMMARY: This action announces the FAA's recommended guidance for the 
voluntary marking of Meteorological Evaluation Towers (METs) erected in 
remote and rural areas that are less than 200 feet above ground level 
(AGL). This guidance will enhance the conspicuity of the towers for low 
level agricultural operations in the vicinity of these towers.

FOR FURTHER INFORMATION CONTACT: Sheri Edgett Baron, Obstruction 
Evaluation Group, Air Traffic Organization, AJV-15, Federal Aviation 
Administration, 800 Independence Avenue, SW., Washington, DC 20591; 
telephone: (202) 267-8783; e-mail: [email protected].


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. See 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.
    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

[[Page 36984]]

responsibilities to manage the navigable airspace safely and 
efficiently. See 14 CFR part 77 and FAA Order 7400.2, Procedures for 
Handling Airspace Matters.
    Part 77 specifies when notice must be filed with the FAA for the 
construction of a structure or alteration of (an existing) structure. 
In filing this notice, the proponent provides the required information 
and submits its marking and lighting plan for that proposal, if 
appropriate. Sponsors are encouraged to review the guidance in Advisory 
Circular No. 70/7460-1, Obstruction Marking and Lighting in devising 
the marking and lighting plan for the proposed structure. In conducting 
the aeronautical study, the FAA considers the proposed structure, 
including the marking and lighting plan, and determines the impact on 
air navigation. If the FAA issues a Determination of No Hazard to Air 
Navigation, the determination may be conditioned on the structure being 
marked and lighted in accordance with the determination. Unless notice 
is required under a separate paragraph of Sec.  77.9, the FAA does not 
study structures under 200 feet AGL at its site.

I. Background

    The FAA has been approached by operators, associations representing 
agricultural operators, and state governments concerning the visibility 
of METs in remote and rural areas that also have low-level flight 
operations. METs are used by wind energy companies to determine 
feasible sites for wind turbines. Some of these towers are less than 
200 feet AGL, usually at 198 feet or less. The 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. The METs that fall under the 200 
foot AGL threshold, specified in Sec.  77.9, are not subject to the 
notice requirements and do not trigger any aeronautical study by the 
    On January 5, 2011, the FAA published a document seeking comments 
on proposed guidance for the voluntary marking of METs less than 200 
feet AGL (76 FR 1326). The FAA agrees that marking these structures 
would enhance the conspicuity of these METs, particularly for low-level 
agricultural operations.
    The document set forth three recommendations for comment. First, 
the FAA recommended that the METs be painted in accordance with the 
criteria contained in Chapter 3, paragraphs 30-33 of AC No. 70/7460-1. 
In particular, paragraph 33 discusses the paint pattern used to mark 
structures based on size and shape. Section (d) of that paragraph 
specifically refers to communication towers and catenary support 
structures, poles, smokestacks and skeletal framework of storage tanks 
and similar structures. The METs addressed in this document are similar 
to the structures identified in this paragraph. Therefore, the FAA 
proposed the guidance recommended for these structures, which is 
alternating bands of aviation orange and white.
    Secondly, the FAA recommended spherical and/or flag markers be used 
in addition to the above paint pattern when additional conspicuity is 
necessary for aviation safety. Paragraph 34 provides recommended 
guidance for the use of spherical and flag markers.
    Lastly, the FAA proposed high visibility sleeves and/or flags on 
the outer guy wires of these METs. While AC No. 70/7460-1 does not 
contain this type of marking, the FAA specifically sought comments as 
whether this type of marking would be feasible and appropriate.

II. Summary of Comments and FAA Response

    The comment period closed on February 4, 2011 and the FAA received 
approximately 460 comments from individuals, aviation associations, 
industry users, aviation businesses, emergency medical services, state 
governments and state departments of transportation. Many comments 
received were in response to the January 10, 2011 fatal accident 
involving a Rockwell International S-2R aircraft that collided with a 
MET during an aerial application in Oakley, California. Most commenters 
supported a goal of improving the safety of certain aviation operations 
in the vicinity of METs that are less than 200 feet in height. Some 
commenters supported various forms of marking the METs not proposed in 
the document, and others supported marking and lighting METs. Only 3 
commenters opposed the proposed guidance.
    The comments covered the following general areas of the proposal: 
marking and lighting METS, the advantages and disadvantages of affixing 
sleeves and spherical marker balls, establishing a database of METs, 
and making the guidance for marking mandatory.
    The American Wind Energy Association (AWEA) and California Wind 
Energy Association favored enhancing pilot safety. AWEA supported 
painting the METs as proposed, but commented that painting the top \1/
3\ of the tower would be sufficient. The National Agricultural Aviation 
Association (NAAA) commented that the marking provisions should apply 
to any tower over 50 feet AGL. NAAA further contends that paint must be 
applied to the entire vertical length of the tower in order to be 
effective. Transport Canada, which recently issued an Advisory Circular 
\1\ for marking of METs, recommend painting the entire support mast.

    \1\ Transport Canada Advisory Circular No. 600-001, Marking of 
Meteorological Towers (Mar. 3, 2011).

    The FAA agrees that painting the entire structure will provide the 
best visibility for pilots. As aerial applicators fly close to the 
vegetation and well below 200 feet AGL, the MET should be visible 
against the terrain as well as the sky. Therefore, the most effective 
painting scheme would entail painting the entire structure with 
alternating bands of aviation orange and white paint, as described in 
AC No. 70/7460-1, paragraphs 30-33. These provisions also recommend 
that the paint should be replaced when faded or otherwise deteriorated.
    The FAA received varying comments on the usage and length of 
sleeves on METs. Several commenters, including AWEA and Iberdrola, 
stated that there is a practical limit as to how much weight the guy 
wires can sustain and a limited percentage of wires can bear the 
additional weight of sheathing. AWEA also stated that sleeves could add 
significant stress, particularly in icing situations, and undermine the 
structural integrity of the tower and lead to failure.
    Commenters indicated that the length of the sleeve should be 
determined on a case-by-case basis, and result in a sheath that is 
sufficient to rise above tall crops or other land cover but still 
remain visible to pilots. The Helicopter Association International 
recommended at least 16 feet of high visibility sleeves on guy wires at 
the anchor point to extend above any surrounding crop. Other commenters 
recommended sheathing in a range of 6-10 feet.
    The FAA received similar comments from Iberdrola, AWEA, NAAA and 
other agricultural associations on the use of spherical marker balls. 
These commenters stated that marker balls can attract significant 
icing, which increase loads on the tower and can lead to tower failure, 
as well as interfere with instrumentation and affect accuracy of MET 
readings. Various agricultural associations and others supported the 
use of spherical marker balls painted aviation orange. EcoEnergy uses 4 
high visibility cable balls on the outer guy wires. Iowa Agricultural 
Aviation Association recommended 8 total

[[Page 36985]]

marker balls. Iberdrola uses 4 marker balls installed just above 
ground-based sheathing to enhance visibility of the furthest extent of 
guy wires and a second set of 4 marker balls installed approximately 45 
meters AGL to enhance visibility of the painted tower segment that 
delineates the tallest extent of the tower. Iberdola strongly 
discouraged consideration of additional maker balls (more than 8) on 
METs as structural integrity limits are encroached upon with further 
    Additionally, a few comments supported the use of marker flags in 
conjunction with spherical marker balls. The commenters also noted that 
flags may be useful as a visual aid, but are subject to rapid 
deterioration from weather conditions such as wind, snow, and ice.
    The FAA concludes that sleeves and spherical marker balls will 
enhance the conspicuity of METs particularly for low flying 
agricultural and other aviation operations. The FAA recommends one high 
visibility sleeve on each guy wire anchor point that will reach a 
height well above the crop or vegetation canopy, and another sleeve 
installed on each of the outer guy wires. The FAA recognizes that 
certain weather conditions may affect the placement and use of high 
visibility sleeves on guy wires, and that the length should be 
determined on a case-by-case basis.
    Spherical markers may have different placement standards, depending 
on the company that manufactures them. Varying placement standards and 
other factors such as weather play a role in the placement of spherical 
markers and flexibility is needed when determining their position on 
the METs. As a general recommendation, that FAA recommends a total of 8 
high visibility spherical marker (or cable) balls of aviation orange 
color attached to the guy wires; four marker balls should be attached 
to guy wires at the top of the tower no further than 15 feet from the 
top wire connection to the tower, and 4 marker balls at or below the 
mid point of the structure on the outer guy wires. As stated 
previously, the FAA recognizes that the varying factors identified 
above may result in the placement or number of marker balls used and 
should be addressed on a case-by-case basis. The use of sleeves should 
not impact the placement of spherical marker balls.
    Existing guidance in AC 70/7460, paragraph 34(b) states that flags 
are used to mark certain structures or objects when it is technically 
impractical to use spherical markers or painting. The FAA recommends 
spherical markers and paint, however, the FAA did not receive 
sufficient data on the use of flags on the guy wires that support METs 
to provide recommendations on their use for these towers.
    NAAA, HAI, and others submitted various recommendations for 
lighting METs. The comments recommended varied uses of red lights and 
white strobe lights. Some commenters also stated that a recommendation 
for lights would require a Notice to Airmen (NOTAM) to be issued when 
the lights were not operational.\2\

    \2\ The FAA notes that a NOTAM is issued for light outages only 
for structures subject to an FAA determination that specifies 

    Lighting studies indicate that red lights are difficult to see 
during the day, and that the most acceptable lighting configuration 
would be the use of a high intensity white strobe. The FAA acknowledges 
that the addition of lights may make METs more visible to agricultural 
and other low flying operations. The FAA concludes, however, that it 
would not be practical to recommend lights for the METs addressed in 
this document. The remoteness of many MET locations does not allow for 
pre-existing power sources, and strobe lights require more power than 
red lights. While solar lights may be a possible option, the FAA has 
not studied solar lighting and therefore, cannot provide 
recommendations for flight visibility.
    Additionally, when the FAA conducts an aeronautical study, it 
reviews many factors in determining whether lighting is necessary. 
These factors include height, location, proximity to an airport, flight 
activity in the area, and complexity of terrain. Without a similar 
evaluation process, the FAA cannot recommend lighting for METs. It is 
important to note that the FAA does not recommending lighting in every 
aeronautical study.
    The State of Minnesota commented that it is important to collect 
and share information METs siting in a timely manner, and that 
recommendations to mark and light METs should not hinder any growth 
aspirations of the wind industry. NAAA proposed that the FAA establish 
a database that catalogues all tower locations, similar to the 
initiative by the State of Wyoming.
    It is not feasible for the FAA to maintain a national database for 
structures that are less than 200 feet AGL and otherwise not subject to 
the notice requirement in part 77. The FAA does not object to a state 
or local jurisdiction maintaining or providing a source of information 
that would inform pilots as to the location or planned location of 
these towers or for some other zoning, planning or public welfare 
    Many commenters responded that marking and lighting of METs should 
be mandatory. The FAA also received comments from the Experimental 
Aircraft Association, the National Association of State Aviation 
Officials, and others recommending changes to part 77 so that the FAA 
may study different structures at heights constructed less than 200 
feet. NAAA also commented that upon adoption of revised standards, any 
towers erected before the adoption date shall be marked within six 
months after the effective date.
    The purpose of this proposal was to address a limited population of 
METs that are not studied under part 77, but are difficult to see by 
certain low level aircraft operations. The guidance is recommended to 
landowners and developers siting these towers in remote, rural 
agricultural areas. The guidance recommended here is not necessary for 
METs that are erected in urban areas and far removed from areas where 
rural agricultural spraying operations are conducted. Landowners and 
developers must exercise discretion in determining if the METs will be 
erected in this type area where these operations are conducted and 
whether the marking and painting would enhance the visibility of these 
structures to low-level flight operations.
    The FAA received comments pertaining to environmental impact issues 
and vegetation management. The Marin Audubon Society supporting the 
inclusion of guidance for measures to reduce the risk of collision for 
aircraft and birds. Other commenters claimed that steady red lights 
attract and confuse birds and that sleeves and skeletal framework of 
METs should be designed to make them visible for birds.
    Three commenters opposed the proposal. One commenter was concerned 
that the proposal would be expanded to include amateur radio antenna 
supports. Another commenter was concerned with light pollution and 
applicability regardless of terrain and other factors. The remaining 
commenter inaccurately referred to this notice of policy as a notice of 
proposed rulemaking to amend the regulations in part 77. This commenter 
also argued that some developers may follow the guidance and others may 
not, which may introduce potential for pilots to presume that all METs 
will be marked and could result in failure to identify and avoid 
unmarked towers. The commenter contends that developers that choose to 
voluntarily mark and

[[Page 36986]]

light their METs would incur additional costs and time delays and this 
affects their ability to compete with others in the market. As stated 
previously, the FAA is not amending the regulations to require notice 
for structures less than 200 feet AGL in non-airport environments. The 
FAA is providing this information to enhance the visibility of 
structures that otherwise may be difficult to see due to the terrain 
and the nature of specific operations conducted around these METs. 
While this guidance is not mandatory, the FAA anticipates that in the 
interest of aviation safety, developers and landowners will consider 
this guidance for METs erected in the environments described in this 

III. Policy

    The FAA recommends voluntary marking of METs less than 200 feet AGL 
in accordance with marking guidance contained in this document and 
Advisory Circular 70-7460-l, Obstruction Marking and Lighting. The FAA 
notes that historically this guidance has not been applied to the 
voluntary marking of METs less than 200 feet AGL. However, the FAA 
recognizes the need to address safety impacts to low-level flight 
operations due to the construction of METs in remote and rural areas, 
especially as agricultural spraying season approaches. Due to the 
growing concerns expressed by operators, associations representing 
agricultural operators, and state and local governments throughout the 
agricultural industry, the FAA believes that voluntary marking of METs 
less than 200 AGL in remote and rural areas enhance the visibility of 
these structures to low level agricultural operations in the vicinity 
of these towers.
    The FAA recommends that landowners and developers use guidance 
contained in Advisory Circular 70/7460-1, Obstruction marking and 
Lighting for the voluntary marking of METs less than 200 feet AGL. METs 
should be painted in accordance to criteria contained in Chapter 3, 
paragraphs 30-33 of AC No. 70/7460-1, specifically, with alternate 
bands of aviation orange and white paint. In addition, paragraph 34 
states that all markings should be replaced when faded or otherwise 
deteriorated. The FAA recommends that high visibility sleeves be 
installed on the outer guy wires of METs as described in this document. 
The FAA intends, at a future date, to amend the advisory circular to 
include guidance on sleeves. Additionally, the FAA recommends high 
visibility spherical marker (or cable) balls of aviation orange color 
are attached to the guy wires. Spherical markers should be installed 
and displayed in accordance to guidance contained in this document and 
additional standards contained in Chapter 3, paragraph 34 of AC No. 70/
70460-1. The FAA, however, recognizes various weather conditions and 
manufacturing placement standards may affect the placement and use of 
high visibility sleeves and/or spherical markers. Thus, flexibility is 
needed when determining sleeve length and marker placement on METs.

    Issued in Washington, DC, on June 20, 2011.
Dennis E. Roberts,
Director, ATO Airspace Services, AJV-1.
[FR Doc. 2011-15746 Filed 6-23-11; 8:45 am]