Aviation Terms

VOR (Very high frequency Omnidirectional Radio)
The backbone of civil aviation radionavigation in the United States. A transmitter on the ground broadcasts a radio signal which is modulated differently in different directions. A receiver aboard the aircraft decodes the signal and determines which direction from the transmitter the airplane is located. Most airplanes have two VOR receivers, so that if one malfunctions, the other can be used. Often it is useful to have two working VORs, so that one can be used to keep the airplane on course, and the other can be used to determine how far along the course the airplane is.
ADF (Automatic Direction Finder)
A radionavigation method that was widely used before the advent of VOR. Although in principle it provides the same information as VOR, it is less accurate and harder to use. A transmitter on the ground called an NDB (non-directional beacon) broadcasts a signal, and an airborne receiver determines the direction from which the signal is arriving.
ILS (Instrument Landing System)
A radionavigation system that can guide an airplane down to a runway in clouds and/or low visibility. Easy to use and accurate, ILS is often successful when the cloud ceiling is as low as 200 feet above the runway.
DME (Distance Measuring Equipment)
A radionavigation system that measures the distance from an aircraft to a transmitter on the ground. Often used in conjunction with VOR.
GPS (Global Positioning System)
A satellite-based navigation system that is the wave of the future not only for aviation, but for all kinds of transportation as well as surveying, outdoor recreation, and many other applications. Originally developed by the military, GPS now has dozens of civilian uses as well. Portable receivers costing less than $200 can put this capability in the hands of almost anyone.
VFR (Visual Flight Rules)
A set of flight operating rules that assumes that the visibility is good enough to fly the airplane with visual reference to the horizon and to approach an airport by visual reference. It is illegal and usually unsafe for a VFR flight to penetrate a cloud.
IFR (Instrument Flight Rules)
A set of flight operating rules that does NOT rely on any visual references, but rather on the airplane's instruments, except where visual flight is specifically required on approach to an airport. IFR flight requires certain equipment in the airplane and that the pilot be instrument rated (which I am).
The orientation of an airplane with respect to the horizon, i.e. whether its nose is pitched up or down, and whether the wings are banked left or right.
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