necessary to avoid it. This may involve following another aircraft or keeping it in sight until it is no longer a factor. 

(See SEE AND AVOID.) (Refer to 14 CFR Part 91.) 

VLF- 

(See VERY LOW FREQUENCY.) 

VMC- 

(See VISUAL METEOROLOGICAL CONDITIONS.) 

VOICE SWITCHING AND CONTROL SYSTEM (VSCS)- A computer controlled switching system that provides air traffic controllers with all voice circuits (air to ground and ground to ground) necessary for air traffic control. 

(Refer to AIM.) 

VOR- A ground-based electronic navigation aid transmitting very high frequency navigation signals, 360 degrees in azimuth, oriented from magnetic north. Used as the basis for navigation in the National Airspace System. The VOR periodically identifies itself by Morse Code and may have an additional voice identification feature. Voice features may be used by ATC or FSS for transmitting instructions/in- formation to pilots. 

(See NAVIGATIONAL AID.) (Refer to AIM.) 

VOR TEST SIGNAL- 

(See VOT.) 

VORTAC- A navigation aid providing VOR azimuth, TACAN azimuth, and TACAN distance measuring equipment (DME) at one site. 

(See DISTANCE MEASURING EQUIPMENT.) (See NAVIGATIONAL AID.) (See TACAN.) (See VOR.) (Refer to AIM.) 

VORTICES- Circular patterns of air created by the movement of an airfoil through the air when generating lift. As an airfoil moves through the atmosphere in sustained flight, an area of area of low pressure is created above it. The air flowing from the high pressure area to the low pressure area around and about the tips of the airfoil tends to roll up into two rapidly rotating vortices, cylindrical in shape. These vortices are the most predominant parts of aircraft wake turbulence and their rotational force is dependent upon the wing loading, gross weight, and speed of the generating aircraft. The vortices from medium to super aircraft can be of extremely high velocity and hazardous to smaller aircraft. 

(See AIRCRAFT CLASSES.) (See WAKE TURBULENCE.) (Refer to AIM.) 

VOT- A ground facility which emits a test signal to check VOR receiver accuracy. Some VOTs are available to the user while airborne, and others are limited to ground use only. 

(See CHART SUPPLEMENT U.S.) (Refer to 14 CFR Part 91.) (Refer to AIM.) 

VR- 

(See VFR MILITARY TRAINING ROUTES.) 

VSCS- 

(See VOICE SWITCHING AND CONTROL SYSTEM.) 

VTA- 

(See VERTEX TIME OF ARRIVAL.) 

VTOL AIRCRAFT- 

(See VERTICAL TAKEOFF AND LANDING AIRCRAFT.) 

