(2)
Routes defined by Air Traffic Control as specific navigational aid radials or courses.

(3)
Routes defined by Air Traffic Control as direct to or between navigational aids.

SUNSET AND SUNRISE - The mean solar times of sunset and sunrise as published in the Nautical Almanac, converted to local standard time for the locality concerned. Within Alaska, the end of evening civil twilight and the beginning of morning civil twilight, as defined for each locality.
SUPER HIGH FREQUENCY/SHF - The frequency band between 3 and 30 gigahertz (gHz). The elevation and azimuth stations of the Microwave Landing System operate from 5031 megahertz to 5091 megahertz in this spectrum.
SURFACE AREA (P/CG) - The airspace contained by the lateral boundary of the Class B, C, D, or E airspace designated for an airport that begins at the surface and extends upward.

SURVEILLANCE APPROACH (P/CG) - An instrument approach wherein the air traffic controller issues instructions, for pilot compliance, based on aircraft position in relation to the final approach course (azimuth), and the distance (range) from the end of the runway as displayed on the controller's radar scope. The controller will provide recommended altitudes on final approach if requested by the pilot. (See PAR Approach)