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Obstructions to Flight

Introduction:

  • Many structures exist that could significantly affect the safety of your flight when operating below 500' AGL, and particularly below 200' AGL despite FAR 91.119 allowing flight below 500' when over sparely populated areas or open water
  • At and below 200' AGL you are operating close to power lines, antenna towers, etc. which may or may not be lit
  • Notice to Airmen (NOTAMs) will typically be published for unlit structures but pilot vigilance is imperative in case the FAA has not yet been notified of outages
Communication Antennas
Figure 1: Communication Antennas

Antenna Towers:

  • Numerous skeletal structures such as radio and television antenna towers exceed 1,000' or 2,000' 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
  • Additionally, new towers may not be on your current chart because the information was not received prior to the printing of the chart

Overhead Wires:

  • 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 highway, railroad tracks, etc.
  • Supporting structures such as guy wires exist here as well
  • Some locations identify these obstructions with unique sequencing flashing white strobe light systems
    • However, many power lines do not require notice to the FAA and, therefore, are not marked and/or lighted
    • Many of those that do require notice do not exceed 200 feet AGL or meet the Obstruction Standard of 14 CFR Part 77 and, therefore, are not marked and/or lighted
  • Pilots are cautioned to remain extremely vigilant, especially in the case of seaplane and/or float equipped aircraft

Unmanned Balloons:

  • The majority of unmanned free balloons currently being operated have, extending below them, either a suspension device to which the payload or instrument package is attached or a trailing wire antenna, or both
  • Good judgment on the part of the pilot dictates that aircraft should remain well clear of all unmanned free balloons and flight below them should be avoided at all times
  • Pilots are urged to report any unmanned free balloons sighted to the nearest FAA ground facility with which communication is established in order to assist FAA ATC facilities to identify and flight follow unmanned free balloons operating in the airspace
Sectional Chart Key West Surveillance Balloon
Figure 2: Key West Balloon Hazard

Conclusion:

  • There are other objects or structures that could adversely affect your flight such as construction cranes near an airport, newly constructed buildings, new towers, etc.
  • Many of these structures do not meet charting requirements or may not yet be charted because of the charting cycle
  • Some structures do not require obstruction marking and/or lighting and some may not be marked and lighted even though the FAA recommended it

References: