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safety risks. At and below 200 feet AGL there are numerous power lines, antenna towers, etc., that are not marked
and lighted and/or charted as obstructions and, therefore, may not be seen in time to avoid a collision. Notices
to Air Missions NOTAM are issued on those lighted structures experiencing temporary light outages. However,
some time may pass before the FAA is notified of these outages, and the NOTAM issued, thus pilot vigilance
is imperative. Additionally, new obstructions may not be on current charts because the information was not
received prior to the FAA publishing the chart.
b. Antenna Towers.
Extreme caution should be exercised when flying less than 2,000 feet AGL because of
numerous skeletal structures, such as radio and television antenna towers, that exceed 1,000 feet AGL with some
extending higher than 2,000 feet AGL. Most skeletal structures are supported by guy wires which are very
difficult to see in good weather and can be invisible at dusk or during periods of reduced visibility. These wires
can extend about 1,500 feet horizontally from a structure; therefore, all skeletal structures should be avoided
horizontally by at least 2,000 feet.
c. Overhead Wires.
Overhead transmission and utility lines often span approaches to runways, natural
flyways such as lakes, rivers, gorges, and canyons, and cross other landmarks pilots frequently follow such as
highways, railroad tracks, etc. As with antenna towers, these power transmission and/or utility lines and the
supporting structures of these lines may not always be readily visible. The wires may be virtually impossible to
see under certain conditions. Spherical markers may be used to identify overhead wires and catenary
transmission lines and may be lighted. In some locations, the supporting structures of overhead transmission lines
are equipped with unique sequence flashing white strobe light systems to indicate that there are wires between
the structures. The flash sequence for the wire support structures will be middle, top, and bottom with all lights
on the same level flashing simultaneously. However, not all power transmission and/or utility lines require notice
to the FAA as they do not exceed 200 feet AGL or meet the obstruction standard of 14 CFR Part 77 and, therefore,
are not marked and/or lighted. All pilots are cautioned to remain extremely vigilant for power transmission and/or
utility lines and their supporting structures when following natural flyways or during the approach and landing
phase. This is particularly important for seaplane and/or float equipped aircraft when landing on, or departing
from, unfamiliar lakes or rivers.
d. Wind Turbines
. The number, size, and height of individual wind turbines and wind turbine farms have
increased over time. The locations of wind turbine farms have also expanded to areas more commonly flown by
VFR pilots and to all regions of the United States. VFR pilots should be aware that many wind turbines are
exceeding 499 feet AGL in height, which may affect minimum safe VFR altitudes in uncontrolled airspace. In
addition, many wind turbines are encroaching on the 700 foot AGL floor of controlled airspace (Class E). Pilots
are cautioned to maintain appropriate safe distance (laterally, vertically, or both). Wind turbines are typically
charted on Visual Flight Rules (VFR) Sectional Charts and/or Terminal Area Charts. For a description of how
wind turbines and wind turbine farms are charted, refer to the
FAA Aeronautical Chart User’s Guide
. Wind
turbines are normally painted white or light gray to improve daytime conspicuity. They are typically lit with
medium
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intensity, flashing red lights, placed as high as possible on the turbine nacelle (not the blade tips), that
should be synchronized to flash together; however, not all wind turbine units within a farm need to be lighted,
depending on their location and height. Sometimes, only the perimeter of the wind turbine farm and an
arrangement of interior wind turbines are lit. Some wind turbine farms use Aircraft Detection Lighting Systems
(ADLS), which are proximity sensor
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based systems designed to detect aircraft as they approach the obstruction.
This system automatically activates the appropriate obstruction lights until they are no longer needed based on
the position of the transiting aircraft. This technology reduces the impact of nighttime lighting on nearby
communities and migratory birds and extends the life expectancy of the obstruction lights. For more information
on how obstructions such as wind turbines are marked and lighted, refer to Advisory Circular 70/7460
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1,
Obstruction Marking and Lighting. Pilots should be aware that wind turbines in motion could result in limitations
of air traffic services in the vicinity of the wind turbine farms.
REFERENCE
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AIM, Para 4-5-1, Radar.
e. Meteorological (MET) Evaluation Towers.
MET towers are used by wind energy companies to determine
feasible sites for wind turbines. Some of these towers are less than 200 feet AGL. These structures are portable,
Potential Flight Hazards
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