brated in hundreds of feet per minute. VFO Variable Frequency Oscillator VFOP Visual Flight Rules Operations Panel VFR Visual Flight Rules VHF Very High Frequency. The portion of the radio spec-
trum from 30 to 300 MHz. VHS Very High Speed
VHSIC-2  Very High Speed Integrated Circuits - phase 2 
VIGV  Variable Integral Guide Vane 
VISTA  Virtual Integrated Software Testbed for Avionics 
VIU  Video Interface Unit 
V/L  VOR/Localizer 
VLSI  Very Large Scale Integration 
VLV  Valve 
V/M  Voltmeter 
Vmo  The maximum airspeed at which an aircraft is certi-
fied to operate. This can be a fixed number or a func-
tion of configuration (gear, flaps,etc.) or altitude, or 
both. 
VNAV  Vertical Navigation 
VNR  VHF Navigation Receiver 
Voispond  A calsel function that would automatically identify an 
aircraft by a voice recording. Voispond is not yet 
implemented. 
VOR  VHF Omnidirectional Radio Range. A system that pro-
vides bearing information to an aircraft. 
VOR/DME  A system in which a VOR and DME station are co-
located. 
VOR/MB  VOR/marker beacon 
VORTAC  A system in which a VOR and a TACAN station are co-
located. 
VOS  Velocity Of Sound 
VOX  Voice Transmission 
VPN  Vendor Part Number 
VR  Takeoff Rotation Velocity 
VRAM  Video Random Access Memory 
VS  Vertical Speed 
VSAT  Very Small Aperture Terminal 

VSCF  Variable Speed Constant Frequency 
VSCS  Voice Switching and Control System 
VSI  Vertical Speed Indicator 

VSL Advisory Vertical Speed Limit advisory may be preventive or
corrective (TCAS). 
VSM  Vertical Separation Minimum 
VSV  Variable Station Vane 
VSWR  Voltage-Standing Wave Ratio. The ratio of the ampli-
tude of the voltage (or electric field) at a voltage max-
imum to that of an adjacent voltage minimum. Vswr 
is a measurement of the mismatch between the load 
and the transmission line. 
VTO  Volumetric Top-Off 
VTOL  Vertical Takeoff and Landing 
W 
WAAS  Wide Area Augmentation System (Method of 
Differential GPS) 
WADGNSS  Wide Area Differential Global Navigation Satellite 
System 
WADGPS  Wide Area DGPS 
WAFS  World Area Forecast System 
WAI  Wing Anti-Ice 
WARC-92  World Administrative Radio Conference (1992) 
WARC-MOB  World Administrative Radio Conference for the Mobile