§ 87.483   Audio visual warning systems.

   An audio visual warning system (AVWS) is a radar-based obstacle
   avoidance system. AVWS activates obstruction lighting and transmits VHF
   audible warnings to alert pilots of potential collisions with
   land-based obstructions. The AVWS operations are limited to locations
   where natural and man-made obstructions exist. The continuously
   operating radar calculates the location, direction and groundspeed of
   nearby aircraft that enter one of two warning zones reasonably
   established by the licensee. As aircraft enter the first warning zone,
   the AVWS activates obstruction lighting. If the aircraft continues
   toward the obstacle and enters the second warning zone, the VHF radio
   transmits an audible warning describing the obstacle.

   (a) Radiodetermination (radar) frequencies. Frequencies authorized
   under § 87.475(b)(8) of this chapter are available for use by an AVWS.
   The frequency coordination requirements in § 87.475(a) of this chapter
   apply.

   (b) VHF audible warning frequencies. Frequencies authorized under
   § 87.187(j), § 87.217(a), § 87.241(b), and § 87.323(b) (excluding 121.950
   MHz) of this chapter are available for use by an AVWS. Multiple
   frequencies may be authorized for an individual station, depending on
   need and the use of frequencies assigned in the vicinity of a proposed
   AVWS facility. Use of these frequencies is subject to the following
   limitations:

   (1) The output power shall not exceed −3 dBm watts for each frequency
   authorized.

   (2) The antenna used in transmitting the audible warnings must be
   omnidirectional with a maximum gain equal to or lower than a half-wave
   centerfed dipole above 30 degrees elevation, and a maximum gain of + 5
   dBi from horizontal up to 30 degrees elevation.

   (3) The audible warning shall not exceed two seconds in duration. No
   more than six audible warnings may be transmitted in a single transmit
   cycle, which shall not exceed 12 seconds in duration. An interval of at
   least twenty seconds must occur between transmit cycles.

   [ 78 FR 61207 , Oct. 3, 2013]

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Subpart R [Reserved]

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Subpart S—Automatic Weather Stations (AWOS/ASOS)

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