Aviation Glossary

In my trip accounts, I often slip into aviation talk. Here's a short set of definitions that may make that more comprehensible. If you're a student pilot or looking at these for authoritative definitions, that's a bad idea. These are only here to help non-pilots read my trip reports, although I try to make them correct, I may skip over something or simplify for my intended audience. See the FAA pilot/controller glossary for real definitions.

Air Traffic Control (ATC)

A catch-all term for all the folks a pilot might be talking to in controlled airspace (or even outside it). ATC is concerned with keeping aircraft operating under IFR separated, helping pilots spot other aircraft and generally advising or controlling aircraft in real time (unlike an FSS).


A weather advisory indicating a hazard to flight for all aircraft over a given area. For example, when prevailing low ceilings are forecast or observed over a given area an IFR AIRMET is issued. Though AIRMETs are nominally for all aircraft, they are much more significant for small aircraft. A more severe aviation weather advisory is called a SIGMET.

Approach Control

The branch of ATC responsible for separating aircraft as they approach congested areas. They have detailed RADAR and generally deal with more aircraft in closer proximity than their brothers in center control.

Approach Plate

The detailed description of an instrument approach. These are the rules to safely conduct a given approach presented in a standard format.

Automated Terminal Information System

A recorded message giving the weather and relevant airport information for aircraft landing and departing. Pronounced Ay-tis.

Back Course

A localizer has a direction associated with it - toward the runway. Sometimes as part of an instrument approach a pilot has to fly the wrong way on the localizer path, which is called flying the back course. This can be confusing because on simple navigation systems, like mine, this means reacting backward to the system. The needle is saying "fly left" but because it's a back course the pilot has to fly right. Often a pilot has to fly a back course in the process of flying a procedure turn on an ILS.

Common Traffic Advisory Frequency (CTAF)

A CTAF is used to allow pilots to communicate their intentions and positions to each other while operating at an uncontrolled field (or one that is functioning as an uncontrolled field when the twoer is closed). At fields with a part-time tower, the tower frequency is usually used. Others use a unicom or multicom frequency, though sometimes a separate frequency is provided.

Center Control

The branch of ATC responsible for the high altitudes and wide open spaces. These guys cover more area than an approach control and generally the aircraft they're separating are farther apart to start with. The RADAR they have access to usually resolves aircraft locations more coarsely.

Class B Airspace

The tightly controlled airspace around a major commercial airport, like LAX. Operating VFR in class B is something of a pain.

Class C Airspace

The controlled airspace around a smaller, but sizable commercial airport, like Burbank. Operating VFR in class C is much less of a hassle than a Class B.

Cleared Approach

In quiet areas, ATC will sometimes clear a pilot to fly any instrument approach at an airport, essentially saying "any approach that's legal is acceptable to me." The term for this is "cleared approach." It almost never happens to me in the LA area.

Courtesy Car

A courtesy car, also called a crew car, is a car provided by an FBO to transient pilots for a fairly short time free of charge or at a nominal charge. This is to run short errands or grab a quick meal. It's a great service.

Distance Measuring Equipment (DME)

DME allows a pilot to determine the airplane's distance from a point on the ground that has a DME station. In and of itself, this is useful, but combined with a VOR, pilots can determine their location with excellent accuracy.

Like VORs, DME is supposed to be replaced by GPS, and in practice often is. Also like VORs, the abbreviation is universally used; no one says “distance measuring equipment.”

DME arc

A DME arc is a technique that allows a pilot to fly a curved course a fixed distance from a given point (navigation system). They're not used much in the busy controlled airspace I fly in around LAX.

Fixed Base Operator (FBO)

FBOs are the nice folks who provide services like fuel, flight planning facilities, phones, access to rental cars, rest rooms, showers, snooze rooms for pilots, and bunches of other useful things. They often have a flight school and some airplanes for rent as well. They're easy people to love.

No one says "fixed base operator" unless they're making a point.

Flight Following

Traffic advsories.

Flight Service Station (FSS)

A set of ground-based information centers that provide information to pilots about weather and other flight conditions. They are separate from ATC, and only deal with fairly slowly developing phenomena. An FSS cannot tell you that another aircraft is nearby, but does have time to read you weather forecasts. Pilots generally get a briefing from one before flight and can also contact them in flight to give or receive information about other conditions.

A pilot speaking to Flight Watch is speaking to an FSS.

Glideslope (GS)

The equipment in an ILS that provides vertical (up/down) guidance to a landing aircraft.

Go Around

To abort a landing. So called because after aborting, the pilot usually continues around the traffic pattern and lands on the next circuit.

The words are used as both noun and verb. One aborts by going around; the procedure is called a go around.

Instrument Approach (IAP)

A detailed IFR procedure intended to allow a pilot to land at an airport that is clouded over. When pilots say things like, "it's an easy approach" or "I had to take the approach" they generally are talking about an instrument approach. Because they're designed to be flown absolutely blind, IAPs are time-consuming.

In nearly all small planes, an IAP will not take a pilot clear to the ground, as commercial jets can. Depending on the equipment in the aircraft and airport, an IAP can usually get a pilot between 800 and 200 feet above the runway and the pilot lands the aircraft visually from there.

Instrument Departure (DP)

A set of instructions to follow under Instrument Flight rules when departing an airport. They guarantee clearance from obstacles and keep all the planes flying the departure going the same way.

Becasue they're meant to be flown blind, they don't always make much sense visually and usually take longer than a visual departure.

Instrument Flight Rules (IFR)

The set of rules that govern instrument flight. Filing IFR or departing IFR means that the pilot is operating under those rules. Aircraft are much more closely controlled under those rules and are permitted to fly through clouds as Air Traffic Control is keeping aircraft separated. To "be IFR" is to operate under these rules under a clearance from ATC. Sometimes pilots (including me) say IFR when we mean IMC, or refer to a field as "being IFR." When a field is IFR, it means that only departures and arrivals under IFR (or in some cases special VFR) are legal.

Instrument Landing System (ILS)

Although it sounds pretty generic, an ILS is a specific set of equipment used to provide a very accurate instrument approach. It provides both lateral (left/right) guidance through a localizer and vertical (up/down) guidance through a glideslope, all of which can be used completely blind outside the cockpit. Even fairly unsophisticated aircraft can use an ILS to get within 200' of most airports and this is the system that specially equipped and trained transport aircraft and pilots can use to land completely blind.

Instrument Meteorological Conditions (IMC)

Weather conditions bad enough that the pilot is controlling the aircraft only by reference to instruments. Basically a pilot in IMC is in a cloud, although there are other places where IMC can prevail.

Localizer (LOC)

A localizer is a very accurate navigation aid used in an ILS for lateral (left/right) guidance to the runway.

Minimum En Route Altitude (MEA)

The lowest altitude an aircraft can legally fly at under IFR on a given route. This is determined by the local terrain and navigation equipment.

Notice to Airmen (NOTAM)

An official notice about outages, temporary flight restrictions, or other transient conditions pilots might care about. These are issued by the FAA and distributed by (among other places) flight service stations.

Pilot Report

A report of actual conditions made by a pilot to ATC or flight service. These both help other pilots know what conditions are actually occurring and help weather forecasters evaluate and improve their predictions.

Pilot's Discretion

An IFR instruction (e.g., altitude change) that can be carried out when the pilot decides to carry it out. This allows a pilot to stay in favorable conditions or avoid unfavorable ones while remaining on an instrument clearance.

Precision Approach Path Indicator

A more accurate VASI. This 4-light visual glideslope indicator is calibrated to display smaller deviations than a VASI.

Procedure Turn

Depending on which way a pilot enters an instrument approach, in may be necessary to turn the aircraft back toward the airport in order to fly the approach. A procedure turn is the safe, controlled, time-consuming way to do this.

Progressive Taxi

Turn-by-turn directions on an airport. A pilot unfamiliar to a field that has a tower can request these directions.

Restricted Airspace

Airspace set aside for the exclusive use of some government agency, usually the military. These are permanent allocations, though the space may be unused at a given time and civilian aircraft allowed in.

Sectional Chart

One of the brightly colored maps of the country used for flying VFR. They have a pretty impressive amount of data from topography to airspace boundaries and points of interest. Don't leave home without them.


A severe aviation weather advisory. The same sorts of things that would cause an AIRMET to be issued can cause a SIGMET to be issued, though a SIGMET means that the conditions are significantly more severe. SIGMETs are of operational importance to even large transport aircraft, and generally highlight conditions like observed thunderstorm systems (including tornadoes) and areas of reported or forecast severe icing. Because the conditions underlying a SIGMET are an issue for even large aircraft, pilots of small aircraft have to take them very seriously.

Special VFR

Make your own bad joke using “special” here.

Special VFR is a clearance to operate in controlled airspace when the weather is worse than required for VFR. Other aircraft are kept out of the area and aircraft operating special VFR have to remain out of the clouds.

Standard Instrument Arrival (STAR)

A standard arrival is an IFR procedure designed to bring traffic into a busy area in an orderly manner. A pilot will encounter one between the en route part of the flight and an instrument approach. They are the arrival equivalent of a instrument departure procedure

Traffic Advisories

ATC is not required to keep VFR traffic separated from other VFR traffic. If their workload permits and the pilot asks, ATC will inform pilots when there is other traffic in the area. I make extensive use of this service, but do recognize its limits. I've seen enough traffic very nearby that ATC didn't see to understand that RADAR is not omniscient.


A transponder is a piece of avionics that replies to a radar signal with a short identifier and (if it knows it) the altitude of the aircraft. This information makes ATC's life easier, which makes the pilot's easier. There are some areas, like class B airspace where a transponder is required.

VFR Flight Following

Traffic advsories.

VHF Omnidirectional Range (VOR)

These are ground-based radio navigational aids scattered around the country. Lines between them, called Victor airways, are the primary instrument flight paths throughout the country.

The actual equipment allows a pilot to determine the magnetic direction the airplane lies from a given VOR. This is a really useful thing to know and VORs have been a primary way of instrument navigation as well as being very helpful in VFR conditions. They are often colocated with DME, making them even more useful.

The FAA is planning to phase VORs out and use GPS everywhere. Even now a lot of flying to and from VORs is really done by GPS equipment that does not depend on the VOR transmitting.

Everyone calls these VORs. The full name is a trivia question. (And one I'd answered incorrectly until Mike Holt pointed it out to me.)

Visual Appraoch

An approach under IFR that is conducted visually rather than using an instrument approach. Almost always easier than shooting a full instrument approach.

Visual Approach Slope Indicator (VASI)

A pair of lights to the side of the runway that tells the pilot that the plane is on a safe and reasonable descent to the runway. Red lights over white is the right thing to see. It's only vertical (up/down) guidance.

Everyone pronounces the acronym rather than expanding it.

Visual Flight Rules (VFR)

If the weather is good enough, pilots can fly by looking out the window and avoiding hazards. There are some rules involved about how close a pilot can come to clouds, restricted or controlled airspace, and ground structures, and those rules are referred to as visual flight rules. Most small plane flying is conducted under VFR. A pilot might also say that the weather is VFR, meaning that the weather is clear enough that flight under visual flight rules is legal, or that an airport is VFR meaning that the weather at that airport is VFR.

Visual Glideslope Indicator

One or more lights that a pilot can use to ensure that the aircraft is on a reasonable descent path for a given runway. These provide guidance purely by visual means; no electronics is involved. The most common types are VASIs and PAPIs.

Visual Meteorological Conditions (VMC)

Weather good enough for VFR flight. Pilots often say VFR when they mean VMC.


Unicom is an unofficial communication frequency used at uncontrolled fields to communicate a variety of information. When there is a tower on the field, it is used to communicate with FBO operators to arrange things like parking, fuel, and other services.

At uncontrolled fields it generally functions as a CTAF on which pilots inform each other of their positions and intentions to avoid conflicts. When the unicom is monitored, services such as airport advisories or weather iformation may be available. Exactly what services are available varies widely.

This page written and maintained by Ted Faber.
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