Instrument Flying Handbook Glossary (part 1)

Terms taken from the glossary of the FAA’s Instrument Flying Handbook

Absolute Accuracy

The ability to determine present position in space independently, a skill often used by pilots

Absolute Altitude

The actual distance between an aircraft and the terrain over which it flies

Absolute Pressure

Pressure measured from the reference of zero pressure or a vacuum

A.C.

Alternating current

Acceleration Error

A magnetic compass error apparent when the aircraft accelerates while flying on an easterly or westerly heading, causing the compass card to rotate toward North

Accelerometer

A part of an inertial navigation system (INS) that accurately measures the force of acceleration in one direction

Adverse Yaw

A flight condition occurring at the beginning of a turn in which the nose starts to move opposite the direction the turn is being made. This is caused by the induced drag produced by the downward-deflected aileron holding the wing back as it rises in the turn

Aeronautical Decision Making (ADM)

A systematic approach to the mental process used by pilots to consistently determine the best course of action in response to a given set of circumstances

Agonic Line

An irregular imaginary line across the surface of the Earth along which the magnetic and geographic poles are in alignment, and there is no magnetic variation

Aircraft Approach Category

A performance grouping of aircraft based on a speed of 1.3 times the stall speed of a given aircraft (in landing configuration, at maximum landing weight)

Air Data Computer (ADC)

An aircraft computer that receives and processes pitot pressure, static pressure, and temperature to calculate very precise altitude, indicated and true airspeed, and air temperature

AIRMET

An inflight weather advisory issued to amend an area forecast, containing information regarding potentially hazardous weather, specifically dangerous to aircraft with limited equipment, instruments, or pilot qualifications

Airport Diagram

The section of an instrument approach procedure chart that shows a detailed diagram of the airport, including surface features and configuration

Airport/Facility Directory (A/FD)

An FAA publication containing information on all airports, communications, and NAVAIDs

Airport Surface Detection Equipment (ASDE)

Radar equipment designed to detect the features and traffic on an airport’s surface, used by control towers to augment visual observation

Airport Surveillance Radar (ASR)

Approach control radar used to detect and display aircraft positions in terminal areas

Airport Surveillance Radar Approach

An instrument approach in which ATC issues instructions based on aircraft position in relation to final approach course and distance from the end of the runway, as displayed on a controller’s radar

Air Route Traffic Control Center (ARTCC)

Provides ATC service to aircraft operating on an IFR flight plan within controlled airspace, mainly during the en route phase of flight

Airspeed Indicator

A differential pressure gauge that measures the dynamic pressure of the air through which the aircraft is flying, using it to display an aircraft’s airspeed to the pilot

Air Traffic Control Radar Beacon System (ATCRBS)

Also know as Secondary Surveillance Radar (SSR), ATCRBS is an interrogating unit that sends a coded sequence to an aircraft’s transponder, which answers the code in a preselected sequence and sends a message back to the ground equipment, providing a strong return signal, positive aircraft identification, and other data

Airway

A route based on a centerline extending from one navigation aid to another, used to establish a round for procedures between terminal areas

Alert Area

An area in which there is a high volume of pilot training or unusual type of aeronautic activity

Almanac Data

Information the GPS can obtain from a satellite, which approximates the orbital locations of all satellites in a constellation and can be used by the GPS receiver to know what satellites to look for at a given time

Alternate Airport

Designated in an IFR flight plan, and used to provide a suitable alternative destination if the intended airport becomes inadvisable

Alternate Static Source Valve

A valve in the instrument static air system that supplies reference air pressure to the altimeter, airspeed indicator, and vertical speed indicator if the normal static port becomes clogged or iced over

Altimeter Setting

Station pressure (barometric pressure at the location the reading is taken) corrected for the station’s height above sea level

Amendment Status

The circulation date and revision number of an instrument approach procedure, printed above the procedure identification

Ammeter

An instrument that measures the amount of current flowing through an electrical load

Aneroid

A sealed, flat capsule made of thin disks of corrugated metal soldered together, evacuated by pumping all the air out of it; the component in an altimeter or barometer that measures the absolute pressure of the air

Aneroid Barometer

An instrument that measures the absolute pressure of the atmosphere by balancing the weight of the air above it against the spring action of the aneroid

Angle of Attack (AoA)

The acute angle formed between the chord line of an airfoil and the direction of the air striking the airfoil

Anti-ice

Preventing the accumulation of ice on an aircraft via a system designed for that purpose

Approach Lighting System (ALS)

A lighting system designed to penetrate the atmosphere far enough from touchdown to give directional, distance, and glide path information for safe transition from instrument to visual flight

Area Chart

Part of the low-altitude en route chart series, this chart gives terminal data at a larger scale for congested areas

Area Navigation (RNAV)

Allows pilots to fly a selected course (via waypoints) to a predetermined point without the need to overfly ground-based navigation facilities

Atmospheric Propagation Delay

A bending of the electromagnetic wave from the satellite that creates an error in the GPS system

Attitude Heading and Reference Systems (AHRS)

A system with three-axis sensors which provides heading, altitude, and yaw information for aircraft. These systems are designed to replace traditional mechanical gyroscopic flight instruments and provide better reliability and accuracy

Attitude Director Indicator (ADI)

An aircraft attitude instrument that incorporated flight command bars to provide pitch and roll commands

Attitude Indicator

The foundation for all instrument flight; reflects the airplanes attitude in reference to the horizon

Attitude Instrument Flying

Controlling the aircraft by reference to the instruments rather than by outside visual cues

Autokinesis

A nighttime visual illusion that causes stationary light to appear as if they are moving, which becomes apparent after several seconds of staring at said light

Automated Weather Observation System (AWOS)

Automated weather reporting system consisting of various sensors, a processor, a computer-generated voice subsystem, and a transmitter to broadcast weather data

Automated Weather Observing System (ASOS)

Weather reporting system which provides surface observations every minute via digitized voice broadcasts and printed reports

Automatic Dependent Surveillance-Broadcast (ADS-B)

A device used in aircraft that repeatedly broadcasts a message that included aircraft position, velocity, and sometimes other information

Automatic Direction Finder (ADF)

Electronic navigation equipment that operates in the low and medium frequency bands. Used in conjunction with the ground-based NDB, this instrument displays the direction from the nose of the aircraft to the station being received

Automatic Terminal Information Service (ATIS)

The continuous broadcast of recorded non-control information in select terminal areas, meant to improve controller effectiveness and relieve frequency congestion by automating repetitive transmission of essential, routine information

Aviation Medical Examiner (AME)

A physician with training in aviation medicine designated by the Civil Aerospace Medical Institute (CAMI)

Azimuth Card

A card that may be set, gyroscopically controlled, or driven by a remote compass

Back Course (BC)

The reciprocal of the localizer course for an ILS. When flying this approach, an aircraft approaches the instrument runway from the end at which the localizer antennas are installed

Baro-aiding

A method of augmenting the GPS integrity solution by using a non-satellite input source. To ensure this method works, the current altimeter setting must be entered as described in the operating manual

Barometric Scale

A scale on the dial of the altimeter to which the pilot sets the barometric pressure level from which the altitude shown by the pointers is measured

Block Altitude

A block of altitudes assigned by ATC to allow altitude deviations; for example, “maintain block altitude nine to eleven thousand”

Cage

The black markings on the ball instrument indicating its neutral position

Calibrated

The instrument indication compared with a standard value to determine the accuracy of the instrument

Calibrated Orifice

A hole of specific diameter used to delay the pressure change, such as in a vertical speed indicator

Calibrated Airspeed

The speed at which the aircraft is moving through the air, found by correcting IAS for instrument and position errors

Changeover Point (CP)

A point along the route or airway segment where changeover between two navigation facilities or waypoints should occur

Circling Approach

A maneuver initiated by the pilot to align the aircraft with a runway for landing when a straight-in landing from an instrument approach is not feasible

Class A Airspace

From 18000’ MSL to FL600, over contiguous states and Alaska with a 12 NM border from the coast

Class B Airspace

From surface to 10000’ MSL surrounding the busiest airports, individually tailored and consisting of two or more layers above the surface. ATC clearance is required to operate within the area

Class C Airspace

From the surface to 4000’ MSL above airport elevation surrounding airports with operating control towers equipped with radar approach control and having a large volume of IFR traffic. Usually consists of a 5NM core and a 10NM shelf 1200’ to 4000’ above airport elevation

Class D Airspace

From surface to 2500’ above airport elevation surrounding airport with an operational control tower, designed to contain instrument procedures

Class E Airspace

Controlled airspace that is not class A, B, C, or D

Class G Airspace

Uncontrolled airspace (except when associated with a temporary control tower)

Clean Configuration

A configuration in which all flight control surfaces have been placed to create minimum drag; in most aircraft this means flaps and gear retracted

Clearance

ATC permission for an aircraft to proceed under specified conditions within controlled airspace

Clearance Delivery

Control tower personnel responsible for transmitting departure clearances to IFR flights

Clearance Limit

The fix, point, or location to which an aircraft is cleared when issued an ATC clearance

Clearance on Request

An IFR clearance not yet received after filing a flight plan

Clearance Void Time

The time at which the departure clearance is automatically cancelled if takeoff has not been made. The pilot must obtain a new clearance if not departed by this time

Clear Ice

Glossy, clear, or translucent ice formed by the relatively slow freezing of large water droplets

Compass Course

A true course corrected for variation and deviation errors

Compass Locator

A low-power, low- or medium-frequency (L/MF) radio beacon installed at the site of the outer or middle marker of an ILS

Compass Rose

A circle split into 360° increments, printed on navigational charts to show the amount of compass variation at different locations, or on instruments to indicate direction

Computer Navigation Fix

A point used to define a navigation track for an airborne computer system such as GPS or FMS

Concentric Rings

Dashed-line circles depicted in the plan view of IAP charts, outside of the reference circle, that show en route and feeder facilities

Cone of Confusion

A cone-shaped volume of airspace directly above a VOR station where no signal is received, causing the CDI to fluctuate

Control Display Unit

A display interfaced with the master computer, providing the pilot with a single control point for all navigation systems, thereby reducing the number of required flight deck panels

Controlled Airspace

An airspace of defined dimensions within which ATC service is provided to IFR and VFR flights in accordance with the airspace classification. Includes Class A, B, C, D, and E airspace

Control Pressures

The amount of physical pressure required on the control column to achieve desired attitude

Convective Weather

Unstable, rising air, such as that found in cumuliform clouds

Convective SIGMET

Weather advisory concerning convective weather significant to the safety of all aircraft; includes tornadoes, hail, and thunderstorms

Coordinated Flight

Flight with a minimum disturbance of the forces maintaining equilibrium, established via effective control use

Coriolis Illusion

The illusion of rotation or movement in a different axis while in a constant rate turn, caused by abrupt head movement

Crew Resource Management (CRM)

The effective use of all available resources: human, hardware, and information

Critical Areas

Areas where disturbances to the ILS localizer and glide slope courses may occur when surface vehicles or aircraft operate near the equipment’s antennas

Cross-check

The first fundamental skill of instrument flight, also called a “scan” of flight deck instruments

Cruise Clearance

An ATC clearance issued to allow a pilot to fly at any altitude from the minimum IFR altitude up to and including the clearance-specified altitude; also allows pilots to proceed to and make an approach at the destination airport

Current Induction

An electrical current being induced into or generated in any conductor that is crossed by lines of flux from any magnet

Dark Adaption

Physical and chemical adjustments of the eye that make vision possible in relative darkness

Deceleration Error

A magnetic compass error that occurs when the aircraft decelerates while flying on an easterly or westerly heading, causing the compás card to rotate toward South

Decision Altitude (DA)

A specified altitude in the precision approach, charted in MSL, at which a missed approach must be initiated if the required visual reference to continue the approach has not been established

Decision Height (DH)

A specified altitude in a precision approach, charted in height above threshold elevation, at which a decision must be made either to continue the approach or execute a missed approach

De-ice

The act of removing ice accumulation from an aircraft structure

Density Altitude

Pressure altitude corrected for nonstandard temperature; used in computing aircraft and engine performance

Departure Procedure (DP)

Preplanned IFR ATC departure, published for pilot use in textual and graphic format

Deviation

A magnetic compass error caused by local magnetic fields within the aircraft, different on each heading

Differential Global Positioning System (DGPS)

A system that improves the accuracy of Global Navigation Satellite Systems (GNSS) by measuring changes in variables to provide satellite positioning corrections

Direct Indication

The true and instantaneous reflection of aircraft pitch and bank altitude by the miniature aircraft, relative to the horizon bar of the attitude indicator

Direct User Access Terminal System (DUATS)

A system that provides current FAA weather and flight plan filing services to certified civil pilots via personal computer, modem, or telephone; pilots can request specific types of weather briefings and other data for planned flights