§ 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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