background image Abbreviation/ Acronym Meaning VASI . Visual Approach Slope Indicator VCOA . Visual Climb Over the Airport VDA . Vertical Descent Angle VDP . Visual Descent Point VFR . Visual Flight Rules VGSI Visual Glide Slope Indicator VHF . Very High Frequency VIP Video Integrator Processor VLOS Visual Line of Sight VMC Visual Meteorological Conditions MINI . . Instrument flight minimum speed, utilized in complying with minimum limit speed requirements for instrument flight VNAV Vertical Navigation NE . Never exceed speed NEI . Instrument flight never exceed speed, utilized instead of V NE for compliance with maximum limit speed requirements for instrument flight VO Visual Observer VOR . Very High Frequency Omni - directional Range VORTAC . VHF Omni - directional Range/Tactical Air Navigation VOT . VOR Test Facility VR VFR Military Training Route REF . The reference landing approach speed, usually about 1.3 times V so plus 50 percent of the wind gust speed in excess of the mean wind speed. Abbreviation/ Acronym Meaning SO . . The stalling speed or the minimum steady flight speed in the landing configuration at maximum weight. VTF . Vector to Final VV Vertical Visibility VVI . Vertical Velocity Indicator . . Speed for best rate of climb YI . . Instrument climb speed, utilized instead of for compliance with the climb requirements for instrument flight WA AIRMET WAAS . Wide Area Augmentation System WFO . Weather Forecast Office WGS - 84 World Geodetic System of 1984 WMO World Meteorological Organization WMS Wide - Area Master Station WMSC . Weather Message Switching Center WMSCR Weather Message Switching Center Replacement WP Waypoint WRA Weather Reconnaissance Area WRS . Wide - Area Ground Reference Station WS SIGMET WSO Weather Service Office WSP . Weather Systems Processor WST . Convective Significant Meteorological Information WW . Severe Weather Watch Bulletin Abbreviations/Acronyms Appendix 3 -