Diverse Vector Area (DVA). An airport may establish a  diverse vector area if it is necessary to vector aircraft below  the minimum vectoring altitude to assist in the efficient  flow of departing traffic. DVA design requirements are  outlined in FAA Order 8260.3 and allow for the vectoring  of aircraft immediately off the departure end of the runway  below the MVA.  Dynamic Magnetic Variation. A field that is simply a  computer model calculated value instead of a measured  value contained in the record for a waypoint.  EFVS Operation. An operation in which visibility conditions  require an EFVS to be used in lieu of natural vision to  perform an approach or landing, determine enhanced  flight visibility, identify required visual references, or  conduct a rollout.  Electronic Flight Bag (EFB). An electronic display system  intended primarily for flight deck or cabin use. EFB devices  can display a variety of aviation data or perform basic  calculations (e.g., performance data, fuel calculations, etc.).  In the past, some of these functions were traditionally  accomplished using paper references or were based on  data provided to the flight crew by an airline’s flight dispatch  function.The scope of the EFB system functionality may also  include various other hosted databases and applications.  Physical EFB displays may use various technologies,  formats, and forms of communication. These devices are  sometimes referred to as auxiliary performance computers  (APC) or laptop auxiliary performance computers (LAPC).  Ellipsoid of Revolution. The surface that results when an  ellipse is rotated about one of its axes.  En Route Obstacle Clearance Areas. Obstacle clearance  areas for en route planning are identified as primary,  secondary, and turning areas, and they are designed to  provide obstacle clearance route protection width for  airways and routes.  Enhanced Flight Vision System (EFVS). An installed aircraft  system which uses an electronic means to provide a display  of the forward external scene topography (the natural or  manmade features of a place or region especially in a way to  show their relative positions and elevation) through the use  of imaging sensors, including but not limited to forward- looking infrared, millimeter wave radiometry, millimeter  wave radar, or low-light level image intensification. An  EFVS includes the display element, sensors, computers and  power supplies, indications, and controls.  Fly-by (FB) Waypoint. A waypoint that requires the use of  turn anticipation to avoid overshooting the next flight  segment.  Floating Waypoints. Floating waypoints represent  airspace fixes at a point in space not directly associated  with a conventional airway. In many cases, they may be  established for such purposes as ATC metering fixes,  holding points, RNAV-direct routing, gateway waypoints,  STAR origination points leaving the en route structure,  and SID terminating points joining the en route structure.  Flight Information Region (FIR). A FIR is an airspace of  defined dimensions within which Flight Information Service  and Alerting Service are provided. Flight Information Service  (FIS) is a service provided for the purpose of giving advice  and information useful for the safe and efficient conduct  of flights. Alerting Service is a service provided to notify  appropriate organizations regarding aircraft in need of search  and rescue aid, and assist such organizations as required.  Flight Level (FL). A flight level is a level of constant  atmospheric pressure related to a reference datum of  29.92 "Hg. Each flight level is stated in three digits that  represents hundreds of feet. For example, FL 250 represents  an altimeter indication of 25,000 feet.  Note: Fix is a generic name for a geographical position  and is referred to as a fix, waypoint, intersection, reporting  point, etc.  Fix. A geographical position determined by visual reference  to the surface, by reference to one or more radio NAVAIDs,  by celestial plotting, or by another navigational device.  Final Approach and Takeoff Area (FATO). The FATO is a  defined heliport area over which the final approach to a  hover or a departure is made. The touchdown and lift-off  area (TLOF) where the helicopter is permitted to land is  normally centered in the FATO. A safety area is provided  around the FATO.  Feeder Route. A feeder route is a route depicted on IAP  charts to designate courses for aircraft to proceed from the  en route structure to the IAF. Feeder routes, also referred  to as approach transitions, technically are not considered  approach segments but are an integral part of many IAPs.  Expanded Service Volume. When ATC or a procedures  specialist requires the use of a NAVAID beyond the  limitations specified for standard service volume, an  expanded service volume (ESV) may be established. See  standard service volume.  Field. See database field.  G-4 