Glossary of Terms & Abbreviations

Flying Terms - What Do They Mean?

AFI - Advanced Ultralight Flight Instructor

AGL - Above Ground Level
A reference for measuring altitude or the height of obstructions based on the elevation of the average terrain in the area. Opposed to MSL.

Control surfaces located on the trailing edge of each wing. They work by moving in opposite directions, one up and one down to produce a “bank” that in turn results in the aircraft turning. They are operated by moving the “stick” from side to side or, on some planes by rotating the “yoke” left and right. The ailerons are the primary “turn” control of an aircraft.

A shape or surface generally consisting of smooth curves designed for smooth passage through the air. When used for the wing on an aircraft it will produce a lifting force as a result of air flowing over and around it.

Airport Landing Direction Indicator
A device which can be easily seen from pattern altitude, which indicates the direction in which landings should be made. These devices come in various designs and shapes and have several names. Among them are: Tetrahedron and Augmented Circle.

The speed a plane is moving through the air.

Airspeed Calibrated
The airspeed that is indicated by an air speed indicator (ASI) that has been calibrated to take into account the errors of that particular indicator and pressure measuring system. Most ASI's have some errors. Calibrated airspeed is the result after correcting for these errors.

ALT - Altimeter
The instrument that tells you what your altitude or height is.

The height of an aircraft above {MSL} mean sea level. It has nothing to do with an aircrafts height above the terrain.

Imagine an aircraft flying 1000ft above the sea towards 500ft cliffs. Before it gets to the cliffs it's at an altitude of 1000ft. After it passes the cliffs the aircraft is still at an altitude of 1000ft, but the ground is now only 500 feet below it.

Altitude is not to be confused with height.

Angle of Attack
The angle formed by and between the chord of the wing and the "Relative Wind". A wing will fly according to this angle of attack.

Angle of Climb
The angle formed by the vertical path the airplane is flying and the Earths surface in a climbing airplane.

Angle of Incidence
The built in angle the wing cord line makes with the longitudal axis (Roll Axis) of the airplane.

ASI - Air Speed Indicator
Fairly obviously, this is an instrument that indicates what your current airspeed is.

Aw - Wing Area
A wings span multiplied by its average cord ~ in sq. ft.

Ball Slip or Skid Indicator
A ball in a curved glass tube that rolls to the bottom center of the tube when the aileron and rudder inputs are properly coordinated.

As to “Balloon” in a landing attempt. An unintentional climb occurring right after the flair. It may be caused by ground effect, excessive airspeed, too much elevator input during the flair or failure to release a bit of elevator back pressure once decent rate has been stopped.

The angle of the horizontal axis of the wings relative to the horizon. For example, when the bank is zero degrees, the wings are level. At a bank of 90 degrees, the wings are vertical. For most planes, the maximum angle of bank in level flight is taken to be 60 degrees, as a rule of thumb.

Behind The Power Curve
A phrase relating to a flight condition whereby the plane needs more power then the engine can deliver. This can happen at any altitude, but is really only dangerous when flying low and slow. Because of the high Angle of Attack required by the low speed and the resulting high drag, more and more power is required to keep the plane in the air. The problem is that even with full throttle, you may not have enough power to gain speed or altitude, nor have the height to trade off for speed and don't dare to reduce the power.

BFI - Basic Ultralight Flight Instructor

Multiple unintentional touchdowns on a single landing attempt as frequently happens after a hard landing in which the pilot flairs a little too high, stalls and the aircraft drops to the runway then bounces back into the air, at times soaring a bit. The bounce can be stopped by the addition of a little throttle as the aircraft starts to drop.

Ceiling - Clouds
The height above the Earths surface of the lowest layer of clouds or obscuring smoke, haze or other phenomena reported as broken or overcast.

CFI - FAA Certified Flight Instructor
The kind of instructor you need to give instruction toward a private or higher pilots license.

CFII - FAA Certified Flight Instructor
Qualified to give instruction in instrument flying.

CG - Center of Gravity
The one point, usually located about ¼ of the way back from the leading edge of the wing and along the centerline of the fuselage, that if the aircraft were to be suspended it would balance in its normal level flight attitude. Because of the aircrafts aerodynamics and the effects of control surface movements on those dynamics, the CG must be located between permissible forward and rear locations if they are to generate enough power to maneuver the aircraft.

Check Lists
Lists of procedures, systems, items, actions and other routine things in or around an aircraft that should be checked on all flights. Examples of check lists include: Pre-flight inspection check list, where the aircraft's physical readiness for flight is checked. Engine start check list, where settings, switches and other things pertaining to safe engine start up and running are checked. Take-off or landing check list, where important things pertaining to these operations are set and checked.

CHT - Cylinder Head Temperature
A good check on the health of the cooling system for your engine.

The compass indicates the direction the aircraft is pointed. The reading should not be confused with the aircrafts track (direction of travel over the ground). Until the GPS came into use, the compass was the navigational instrument of choice for use in light aircraft.

Coordinated Flight
The control of the flight of an aircraft is like nothing a new student pilot has ever experienced. Because of the nature of an aircrafts balance and aerodynamics, all of its controls are interrelated, aerodynamically. To accomplish coordinated flight, all of the controls must be correctly used or applied. Move one control and all controls will be affected. This can and does generate many questions, confusion and sometimes just plain wrong ideas about flight control. The student should not despair, after a few hours of instruction they will get the hang of it and with practice usually turn out to be competent pilots.

The straight line distance between the leading and trailing edges of a wing.

The angle between the direction the plane is pointing (heading) and the path it actually travels over the ground (track). To "crab" is to turn the plane a small amount from its intended direction of flight in order to compensate for wind drift that otherwise would carry the plane to the side of the intended track.

Crow Hop(s)
An intentional takeoff to a low height followed by an immediate landing, which may be repeated several times on one run down the runway.

Dihedral Angle
The angle, as seen from the front of the aircraft, formed by the bottom surfaces of both wings, over the top, subtracted from 180 DEG'S. This angle has a lot to do with the longitudinal stability of the aircraft. In light aircraft these angles are approximately A) High Wing ~ 2 Deg's B) Mid Wing ~ 4 Deg's & C) Low Wing ~ 6 Deg's. Generally, less angles result in less positive stability and greater angles more stability.

The tail of an airplane, consisting of the the vertical stabilizer and rudder together with horizontal stabilizer and elevators.

ETA - Expected Time of Arrival

EGT - Exhaust Gas Temperature
A good check on the mixture and delivery of fuel from the carb(s) to your engine.

ETE - Expected Time Enroute

FBO - Fixed Base Operator
Fixed Base Operators are businesses usually located at airfields that provide aviation services to the flying public. These services include the sale of aircraft fuels, maintenance, ground and flying instruction, the rental of aircraft, hangars and tie-downs, to name a few.

The phase of a landing in which the vertical decent speed of an airplane is reduced in anticipation of touchdown. The "flair" refers to the transition from a descending to a horizontal flight path.

A control surface attached to the trailing edge of a wing that combines the action of ailerons and flaps. Flapperons achieve aileron action to produce a bank by moving in opposition (one goes up; the other goes down) and achieve the action of flaps by moving either up or down together while still being able to move in opposite directions for banking.

Inflight adjustable surfaces attached to the trailing edge of the wing (sometimes to the leading edge on more sophisticated airplanes) that alter the flight characteristics of the wing. "Lowering the flaps" increases the lift at the expense of increased drag.

The main fore and aft structure of an airplane where the pilot and passengers sit.

GPS - Global Positioning by Satellite
GPS is a godsend to pilots. It displays an accurate position and ground speed. Some advanced units also have a moving map display and read out the altitude. Th1s instrument renders all the other navigational equipment in airplanes redundant.

Ground Effect
A general term that refers to the increased lift exhibited by a wing when it operates near the ground. The ground effect diminishes with increasing altitude and become negligable when the altitude becomes equal to about one wingspan.

The speed that a plane is moving relative to the ground. With no wind, the ground speed will be the same as the airspeed. But when the wind is blowing, airspeed and ground speed will not be the same.

The direction the plane is pointing. The compass is the heading indicator in an ultralight aircraft.

The vertical distance between an aircraft and the terrain below.

Imagine an aircraft flying at an altitute of 1000ft above the sea and approaching 500ft cliffs. Before it gets to the cliffs it's height and altitude is 1000ft. After it passes the cliffs the aircraft is at a height of 500ft, but its altitude is still 1,000 feet.

IFR - Instrument Flight Rules
The system of rules and regulations established for flying without visual reference to the horizon or to landmarks on the ground. The term is also used, with tongue in check, by some pilots to indicate their mode of flying, as in "I follow rivers, roads, or railroads."

Kn (or Kt ) - Knot
A measure of speed equal to one nautical mile per hour, or 1.15 mph.

A polymer-based (plastic) material that is highly transparent.

Lp - Power Loading
The aircrafts weight divided by the engine HP. Most ultralights operate at a Lp of between 15 and 25 lbs/HP.

Note: Successful ultralight aircraft have been found to operate at maximum of 30 when the Lw and Lp are added together.

Lw - Wing Loading
The aircrafts weight divided by its wing area. Must ultralights operate at a Lw of between 3 and 7 lbs/ft squared.

Maneuvering Speed
The highest speed allowable for abrupt flight control inout. Below this speed the wing will stall before a maneuver can over stress the airframe.

MPH - Miles Per Hour

Mean sea level; reference for measuring altitude based on average (or mean) sea level.

Mush or Mushing
A flight condition were an aircraft is very close to the stall or critical angle of attack and seems reluctant to stall but seems to bog down instead in a relatively low sink rate decent.

Navaids - Aids to Navigation
In aviation, refers generally to VOR's and NDB's.

NDB - Non-Directional Beacon
This is simply a radio transmitter that sends out a signal.

Nautical Mile
A distance of 6,080 feet or 1.15 statute miles. Based on the distance covered by one minute of arc radiating out from the center of the Earth and measured along the surface of the Earth.

P Factor
A force that tends to yaw the nose of a plane to the right or left, depending on the direction of propeller rotation, when in a powered climb. The steeper the climb and the slower the airspeed the greater the force will be. This force may be countered by application of opposite rudder.

PAPIs - Precision Approach Path Indicators
A PAPI is a very bright light put at the end of a runway to allow you to fly in at the correct angle. It shows a white light when you are above the correct glideslope and a red light when you are below the correct glideslope (aircraft are meant to glide in to land, this means that if an engine fails at the last moment it doesn't matter because you are already gliding). They are usually installed in groups of four. A normal approach would use a 3º slope so the lights would be set at 2.7º, 2.9º, 3.1º and 3.3º. This means that the correct 3º slope would show 2 red and 2 white lights. Four whites means you are far too high and you should consider abandoning the approach and trying again. Four reds means you are destined to hit the floor before you reach the runway. Four whites bad, four reds very bad.

PIC - Pilot in Command
The person who bears the ultimate responsibility for the safe and lawful operation of an aircraft. In the case of an flight crew, the pilot in command may not be the person actually doing the flying.

Refers to the nose-high or nose-low attitude of an airplane relative to the horizon.

Pitch Axis
An imaginary horizontal line running through the length of the wing and passing through the aircraft C.G.. The aircraft raises and lowers its nose about this axis. These pitch movements are controlled by the elevators.

Pitot Tube
A small open-ended tube typically no larger than one-quarter inch in diameter that extends forward into air that is largely undisturbed by the aerodynamics of the plane. Air impinging on the front of the tube produces a pressure that the ASI translates to airspeed.

PPC - Powered Parachute

Pressure Altitude
Height, based on the standard atmospheres sea level pressure. (See Standard Pressure)

Prohibited Area
Airspace designated on flying charts and maps that indicate areas over which flying in airspace is prohibited.

PSRU - Propeller Speed Reduction Unit
Otherwise known as the “prop drive” or “redrive”.

An aircraft that has the propeller mounted at the rear of the engine and seems intent on pushing the engine or plane forward.

Relative Wind
The relative direction the air is moving, relative to a wing, as it approaches the wing. Since this direction is relative to the wing and it’s direction of motion, it has no orientation with the ground, earth or horizon as far as the wing is concerned. What is important about the relative wind is the angle it forms with the wing's cord, as it is this angle, which to a very large degree, that determines the lift, drag and stall of the wing.

Restricted Area
Airspace designated on flying charts and maps that indicate areas, while not wholly prohibited, are subject to restriction. Flight in this airspace may be authorized by the controlling facility, also shown on the charts and maps.

Roll Axis
An imaginary horizontal line running through the length of the fuselage and passing through the C.G., about which the aircraft rotates into or out of a bank. These movements are controlled be the ailerons or Flaperons.

The movable vertical surface on the tail of an airplane that controls yaw, the side-to-side movement of the nose of the plane. Typically operated by two foot pedals in the cockpit.

Sectional Chart
Maps intended primarily for persons flying and navigating by visual reference to landmarks. Each “sectional” covers only a section of a geographic area. Sectionals show cities and towns, major highways, rivers, obstructions, as well as airports, navaids, etc. The scale on a sectional is 1 : 500,000. (Approx. 8 statute miles to the inch.)

Sink or Sink Rate
A downward vertical speed, as may be indicated on a VSI, Variometer or the pit of your stomach.

An undesirable flight condition in a turn in which centrifugal force causes the plane to slide toward the outside of the turn. A skid results when the rudder input is excessive for the angle of bank and stick backpressure.

The opposite of a skid. A flight condition in which the plane is banked and slides through the air toward the low wing. Not to be confused with a Slip to Landing.

Slip to Landing
A purposeful flight attitude whereby the aircraft is put into a steep decent by cross controlling the Alerons and Rudder. That is to say, left rudder and right aleron for a slip to the right. This results in a steep and controlable dive with very little if any increase in airspeed.

Spin or Tailspin
A flight condition in which one or both wings are stalled with the plane descending in a steep nose-down attitude together with a fairly rapid rate of rotation. Typically regarded as a dangerous maneuver as considerable altitude is required for recovery.

Stabilizer - Horizontal
The fixed horizontal part of the tail of an airplane.

Stabilizer - Vertical
The fixed vertical part of the tail of an airplane.

Stall or Wing Stall
Loss of sustaining lift generated by the wing due to excessive angle of attack and separation of airflow from the top surface of the wing.

Standard Pressure
Whenever flying and unsure of the current barametric pressure, the pilot should set the standard pressure into the altimeter. The standard pressure setting in USA is 92.29, Canada and Europe is 1013.2. (See Presure Altitude)

Static Air
Refers to the undisturbed barometric pressure in the vicinity of an airplane, or to the system provided for sensing this pressure. A static air pressure source is required for the ASI, VSI, and altimeter. The air pressure inside the nose of an ultralight is usually adequate for this purpose.

Tail Dragger
Aircraft landing gear arrangement having a tail wheel with the main wheels located forward of the planes C.G..

Tail Feathers
The surfaces that make up the tail of an airplane, namely rudder, elevators, and stabilizers.

In flying, a thermal is a sharply defined column of rising air. A thermal is likely to occur over a surface that readily absorbs and reflects heat, then communicates this heat to the air. A sharp bump is ofen felt when a plane flies through a thermal.

Traffic Advisories
Radio information about airport and aircraft operations on or around non-towered airports. The information may be requested by tuning your radio to the frequency used at the airport for communications and transmitting a request for "traffic or field advisories", preceded with the airport name and your aircraft type and identification.

Traffic Pattern - Sometimes Called Circuits
The FAA has established standard rules for flight operations such as, taking off, departing, approaching and landing at airfields. These rules are a pilot's bible for safely operating around airports. See "Piloting & Navigation"

Tricycle Landing Gear
Aircraft landing gear arrangement having a nose wheel and the main wheels located to the rear of the planes C.G..

The control that increases or decreases the engine RPM. This is the primary climb and decent control of the aircraft.

The forward directed force that moves a plane through the air.

Thrust Line
The line of action of thrust. For propeller-driven planes, the thrust line passes through the center of the prop shaft.

The direction of travel of an airplane relative to the ground. Because of sideways drift caused by the wind, the track may not be in exactly the same direction as the plane's heading.

A term that refers to the location of an aircraft engine in the front of the fuselage or on the leading edge of the wing with the prop out in front of the engine.

Trim Tab
A small aerodynamic surface typically attached to the rearmost part of the rudder, aileron, or elevator that produces a deflection of the control surface without input from the pilot. Used to trim (establish the desirable hands-off attitude) the plane. Elevator trim is most common. A trim tab may be only ground adjustable or it may be in-flight adjustable via a control located in the cockpit.

Turn Coordinator
The turn coordinator gauge shows how coordinated a turn is. (See "Piloting & Navication" from the Main Page Menu)

UL - Ultralight Aircraft
Very basic and light aircraft that meets the requirements of 4910.13 Part 103 of the Federal Aviation Regulations. Part 103 states, a powered aircraft with a maximum weight of 254 pounds, capable of carrying only one person, a maximum stall speed of 28 mph, maximum level speed of 63 mph and carrying a maximun of 5 gallons of fuel.

The Variometer gives the same readings as the VSI but because of internal electronic data conditioning circuits there is less lag time in its display and is widely used by the glider and soaring communities. It can operate on 9V battery power.

Pertaining to the distance one can see and identify objects. In aviation, there are several types of visibility, like ground and runway visibility. Each has its own ramifications to flight operations.

VFR - Crusing Altitudes
These are rules set by the Federal Aviation regulations for cruising altitude. These rules only apply when flying 3,000 ft. or higher above the ground. For VFR flight, they state that when flying in a generally Easterly direction, (0º - 179º), the airplane should fly at odd thousands of feet, plus 500 feet. When flying generally Westerly, (180º - 359º), the altitude flow should be even thousands of feet, plus 500 feet. It may be wise to remember that IFR traffic may be flying just 500 feet above or below you!

VFR - Visual Flight Rules
The rules you have to follow when flying in VMC.

Generally clear of clouds and with visual reference (sight) with the horizon and ground.

VMC - Visual Meterological Conditions
This is a complex phrase for a very simple concept. "Visual Meteorological" means "when the weather is good enough for you to see things", ie. no clouds, no fog. Without an instrument rating, the private pilots license only allows you to fly in VMC, meaning you must stay clear of clouds and you must be able to see the horizon and ground at all times.

VNE - Velocity Never Exceed (Airspeed)
The maximum speed approved for safe stress levels on an airplane.

VOR - VHF Omni Range
A very complicated radio transmitter, located on the ground, which transmits 2 signals at the same time. Thus allowing an instrument in the cockpit to work out where the airplane is in relation to that ground based transmitter beacon. This instrument (also called a VOR) has a needle which swings left and right of a vertical line representing the course set into it with the provided knob. A scale around the outside of the instruments face shows the chosen course. To fly a specific course to or from the beacon the needle will swing left or right to tell you which way to fly. Needle to the left, fly left, needle to the right, fly right. The instrument will also indicate whether you are going TO or FROM the beacon on the set in course.

VSI - Vertical Speed Indicator
A sensitive barometric instrument, which displays the rate of ascent or descent of an aircraft in increments of 100’s of feet per minute. It is most useful for climbing or descending at a specific rate. Some pilots find it somewhat useful for finding and evaluating thermals when soaring, although the Variometer is the preferred instrument for this purpose.

Wake Turbulence
Air turbulence resulting from the passage of an aircraft. The turbulent air may be at and/or below the passing plane altitude or may be along the ground in the case of a plane taking off or landing. The heavier the aircraft, the more severe the turbulence wake is likely to be.

This wake will move outward, backward and downward from a passing plane at a rate of about 500 feet per minute for a period of about two (2) minutes and can cause problems for passing aircraft as far back as two miles and 1,000 ft. below the aircraft before dissipating. Therefore, if you are approaching a passing plane which is at a higher altitude, be aware you may fly into that planes wake up to two minutes following its passing.

Wind speed
The speed the air (wind) is moving relative to the ground.

WOT - Wide Open Throttle
Full engine power.

Yaw Axis
An imaginary vertical line passing through the C.G. (center of gravity) of the plane. It’s about this axis the aircraft “wags it’s tail” meaning the whole tail moving from side to side. These movements are controlled by the rudder, which in turn is controlled by the foot peddles in the cockpit.