Aeronautical Terms beginning with I

I Say Again

The message will be repeated.

IAF

Initial Approach Fix.

IAP

Instrument Approach Procedures.

IAS

Indicated Airspeed.

IAS

Indicated Airspeed.

IAWP

Initial Approach Waypoint

ICA

Initial Climb Area

ICAO

International Civil Aviation Organization.

ICAO

International Civil Aviation Organization.

Ice crystals

A type of precipitation composed of unbranched crystals in the form of needles, columns, or plates; usually having a very slight downward motion, may fall from a cloudless sky.

Ice Crystals

Ice crystals, which are often in high concentrations near convective weather systems and lower concentrations in stratus or cirrus clouds, can accrete within turbine engines and cause power loss when in high concentrations. Ice crystals are not typically detected by either conventional ice detectors or airborne radar, and typically do not accrete on external airframe surfaces.

Ice fog

A type of fog composed of minute suspended particles of ice; occurs at very low temperatures and may cause halo phenomena.

Ice needles

A form of ice crystals.

Ice pellets

Small, transparent or translucent, round or irregularly shaped pellets of ice. They may be (1) hard grains that rebound on striking a hard surface or (2) pellets of snow encased in ice.

Icing

In general, any deposit of ice forming on an object. Types include clear icing, rime icing, and glaze.

Icing

The accumulation of airframe ice. Types of icing are: Rime Ice, Clear Ice, Mixed.

Icing Envelopes

Icing envelopes used for the certification of aircraft for flight in icing conditions specify atmospheric icing conditions in terms of altitude, temperature, Liquid Water Content (LWC), and drop size represented by the Median Volume Diameter (MVD). The envelopes use the term mean effective diameter, but this equates to the MVD for the instrumentation and assumptions current at the time the envelopes were established.) There are two classes of icing envelopes: continuous maximum and intermittent maximum. The continuous maximum is for stratus-type clouds, and the intermittent maximum is for cumulus-type clouds.

Icing Intensity

Trace, Light, Moderate, Severe.

ICR

Integrated collaborative rerouting (ICR) is a process that builds on FEA/FCAs. The ICR process requires that a constraint is identified early. Traffic management may issue a planning (PLN) advisory describing the system constraint and providing route guidance. System stakeholders are allowed an opportunity to consider the area of concern, and provide early intent (EI) messages that communicate their decisions in response to the constraint. EI messages update enhanced traffic management system (ETMS) flight trajectories, monitor alert values and routing intentions. At the expiration of the EI window, traffic management can then analyze the customer responses and decide if the actions taken have resolved the issue, or if recommended routes, required routes, airspace flow programs (AFP) and/or other traffic management initiatives (TMIs) will be necessary to further reduce demand. ICR allows system stakeholders flexibility in managing their flights based on an identified NAS constraint, reducing the possibility of more restrictive initiatives. Traffic flow management (TFM) tools benefit from enhanced flight information and collaborative responses to system capacity actions.

Ident

Air Traffic Control request for a pilot to push the button on the transponder to identify return on the controllers scope.

Ident

Air Traffic Control request for a pilot to push the button on the transponder to identify return on the controller’s scope.

Idle thrust

The jet thrust obtained with the engine power control level set at the stop for the least thrust position at which it can be placed.

IF

Intermediate Fix

If No Transmission Received For (Time)

Used by ATC in radar approaches to prefix procedures which should be followed by the pilot in event of lost communications.

IFR

Instrument Flight Rules.

IFR

Instrument Flight Rules. A set of rules governing the conduct of flight under instrument meteorological conditions.

IFR (Instrument Flight Rules)

Rules that govern the procedure for conducting flight in weather conditions below VFR weather minimums. The term “IFR” also is used to define weather conditions and the type of flight plan under which an aircraft is operating.

IFR Aircraft

An aircraft conducting flight in accordance with instrument flight rules.

IFR conditions

Weather conditions below the minimum for flight under visual flight rules.

IFR Conditions

Weather conditions below the minimum for flight under visual flight rules.

IFR Departure Procedure

IFR Takeoff Minimums And Departure Procedures.

IFR Flight

IFR Aircraft.

IFR Landing Minimums

Landing Minimums.

IFR Military Training Routes (IR)

Routes used by the Department of Defense and associated Reserve and Air Guard units for the purpose of conducting low-altitude navigation and tactical training in both IFR and VFR weather conditions below 10,000 feet MSL at airspeeds in excess of 250 knots IAS.

IFR over-the-top

With respect to the operation of aircraft, the operation of an aircraft over-the-top on an IFR flight plan when cleared by air traffic control to maintain “VFR conditions” or “VFR conditions on top”.

IFR Takeoff Minimums And Departure Procedures

Title 14 Code of Federal Regulations Part 91, prescribes standard takeoff rules for certain civil users. At some airports, obstructions or other factors require the establishment of nonstandard takeoff minimums, departure procedures, or both to assist pilots in avoiding obstacles during climb to the minimum en route altitude. Those airports are listed in FAA/DOD Instrument Approach Procedures (IAPs) Charts under a section entitled “IFR Takeoff Minimums and Departure Procedures.” The FAA/DOD IAP chart legend illustrates the symbol used to alert the pilot to nonstandard takeoff minimums and departure procedures. When departing IFR from such airports or from any airports where there are no departure procedures, DPs, or ATC facilities available, pilots should advise ATC of any departure limitations. Controllers may query a pilot to determine acceptable departure directions, turns, or headings after takeoff. Pilots should be familiar with the departure procedures and must assure that their aircraft can meet or exceed any specified climb gradients.

IFSD

In-Flight Shutdown.

Igniter Plugs

The electrical device used to provide the spark for starting combustion in a turbine engine. Some igniters resemble spark plugs, while others, called glow plugs, have a coil of resistance wire that glows red hot when electrical current flows through the coil.

Illustrated talk

An oral presentation where the speaker relies heavily on visual aids to convey ideas to the listeners.

ILS

Instrument Landing System.

ILS

Instrument Landing System. A ground based precision approach system that provides course and vertical guidance to landing aircraft.

ILS Categories

1. Category I. An ILS approach procedure which provides for approach to a height above touchdown of not less than 200 feet and with runway visual range of not less than 1,800 feet. 2. Special Authorization Category I. An ILS approach procedure which provides for approach to a height above touchdown of not less than 150 feet and with runway visual range of not less than 1,400 feet, HUD to DH. 3. Category II. An ILS approach procedure which provides for approach to a height above touchdown of not less than 100 feet and with runway visual range of not less than 1,200 feet (with autoland or HUD to touchdown and noted on authorization, RVR 1,000 feet). 4. Special Authorization Category II with Reduced Lighting. An ILS approach procedure which provides for approach to a height above touchdown of not less than 100 feet and with runway visual range of not less than 1,200 feet with autoland or HUD to touchdown and noted on authorization (no touchdown zone and centerline lighting are required). 5. Category III: a. IIIA.-An ILS approach procedure which provides for approach without a decision height minimum and with runway visual range of not less than 700 feet. b. IIIB.-An ILS approach procedure which provides for approach without a decision height minimum and with runway visual range of not less than 150 feet. c. IIIC.-An ILS approach procedure which provides for approach without a decision height minimum and without runway visual range minimum.

ILS Category I

Provides for approach to a height above touchdown of not less than 200 feet, and with runway visual range of not less than 1,800 feet.

ILS Category II

Provides for approach to a height above touchdown of not less than 100 feet and with runway visual range of not less than 1,200 feet.

ILS Category IIIA

Provides for approach without a decision height minimum and with runway visual range of not less than 700 feet.

ILS Category IIIB

Provides for approach without a decision height minimum and with runway visual range of not less than 150 feet.

ILS Category IIIC

Provides for approach without a decision height minimum and without runway visual range minimum.

ILS PRM Approach

An instrument landing system (ILS) approach conducted to parallel runways whose extended centerlines are separated by less than 4,300 feet and the parallel runways have a Precision Runway Monitoring (PRM) system that permits simultaneous independent ILS approaches.

ILS/PRM

Instrument Landing System/Precision Runway Monitor

IM

ILS Inner Marker.

IMC

Instrument Meteorological Conditions.

IMC

Instrument Meteorological Conditions

Immediately

Used by ATC or pilots when such action compliance is required to avoid an imminent situation.

Impact Ice

Ice that forms on the wings and control surfaces or on the carburetor heat valve, the walls of the air scoop, or the carburetor units during flight. Impact ice collecting on the metering elements of the carburetor may upset fuel metering or stop carburetor fuel flow.

Impingement

The striking and adherence of a water droplet on an aircraft surface. The impingement rate is the rate at which droplets of a given size collect on a particular surface. In general, impingement rates are higher for larger drops and smaller components, such as a very high frequency (VHF) or a Global Positioning System (GPS) antenna.

In-flight shutdown (IFSD)

For ETOPS only, when an engine ceases to function (when the airplane is airborne) and is shutdown, whether self induced, flightcrew initiated or caused by an external influence. The FAA considers IFSD for all causes: for example, flameout, internal failure, flightcrew initiated shutdown, foreign object ingestion, icing, inability to obtain or control desired thrust or power, and cycling of the start control, however briefly, even if the engine operates normally for the remainder of the flight. This definition excludes the airborne cessation of the functioning of an engine when immediately followed by an automatic engine relight and when an engine does not achieve desired thrust or power but is not shutdown.

Inclinometer

An instrument consisting of a curved glass tube, housing a glass ball, and damped with a fluid similar to kerosene. It may be used to indicate inclination, as a level, or, as used in the turn indicators, to show the relationship between gravity and centrifugal force in a turn.

Inclinometer

Increase Speed To (Speed)

Speed Adjustment.

Indefinite ceiling

A ceiling classification denoting vertical visibility into a surface based obscuration.

Index Point

A location specified by the aircraft manufacturer from which arms used in weight and balance computations are measured. Arms measured from the index point are called index arms.

Indicated Airspeed (IAS)

The direct instrument reading obtained from the airspeed indicator, uncorrected for variations in atmospheric density, installation error, or instrument error. Manufacturers use this airspeed as the basis for determining airplane performance. Takeoff, landing, and stall speeds listed in the AFM or POH are indicated airspeeds and do not normally vary with altitude or temperature.

Indicated airspeed (IAS)

Shown on the dial of the instrument airspeed indicator on an aircraft. Directly related to calibrated airspeed (CAS), IAS includes instrument errors and position error.

Indicated Altitude

The altitude read directly from the altimeter (uncorrected) when it is set to the current altimeter setting.

Indirect indication

A reflection of aircraft pitch-and-bank attitude by the instruments other than the attitude indicator.

Indirect indication

A reflection of aircraft pitch-and-bank attitude by instruments other than the attitude indicator.

Induced Drag

That part of total drag which is created by the production of lift. Induced drag increases with a decrease in airspeed.

Induced drag

Drag caused by the same factors that produce lift; its amount varies inversely with airspeed. As airspeed decreases, the angle of attack must increase, in turn increasing induced drag.

Induction icing

A type of ice in the induction system that reduces the amount of air available for combustion. The most commonly found induction icing is carburetor icing.

Induction icing

A type of ice in the induction system that reduces the amount of air available for combustion. The most commonly found induction icing is carburetor icing.

Induction Manifold

The part of the engine that distributes intake air to the cylinders.

Inertia

The opposition which a body offers to a change of motion.

Inertial Navigation System

An RNAV system which is a form of self-contained navigation.

Inertial navigation system (INS)

A computer-based navigation system that tracks the movement of an aircraft via signals produced by onboard accelerometers. The initial location of the aircraft is entered into the computer, and all subsequent movement of the aircraft is sensed and used to keep the position updated. An INS does not require any inputs from outside signals.

Inertial navigation system (INS)

Inflight Refueling

Aerial Refueling.

Inflight Weather Advisory

Weather Advisory.

Initial Approach

The segment between the initial approach fix and the intermediate fix or the point where the aircraft is established on the intermediate course or final approach course.

Initial approach fix (IAF)

The fix depicted on IAP charts where the instrument approach procedure (IAP) begins unless otherwise authorized by ATC.

Initial Approach Segment

Segments Of An Instrument Approach Procedure.

Initial Climb

This stage of the climb begins when the airplane leaves the ground, and a pitch attitude has been established to climb away from the takeoff area.

Initial Climb Area (ICA)

An area beginning at the departure end of runway (DER) to provide unrestricted climb to at least 400 feet above DER elevation.

Inner Marker

A marker beacon used with an ILS (CAT II) precision approach located between the middle marker and the end of the ILS runway, transmitting a radiation pattern keyed at six dots per second and indicating to the pilot, both aurally and visually, that he/she is at the designated decision height (DH), normally 100 feet above the touchdown zone elevation, on the ILS CAT II approach. It also marks progress during a CAT III approach.

Inner Marker Beacon

Inner Marker.

Inner-Approach OFZ

The inner-approach OFZ (Obstacle Free Zone)is a defined volume of airspace centered on the approach area. The inner-approach OFZ applies only to runways with an approach lighting system. The inner-approach OFZ begins 200 feet from the runway threshold at the same elevation as the runway threshold and extends 200 feet beyond the last light unit in the approach lighting system. The width of the inner-approach OFZ is the same as the runway OFZ and rises at a slope of 50 (horizontal) to 1 (vertical) from the beginning.

Inner-Transitional OFZ

The inner transitional surface OFZ (Obstacle Free Zone) is a defined volume of airspace along the sides of the runway and inner-approach OFZ and applies only to precision instrument runways. The inner-transitional surface OFZ slopes 3 (horizontal) to 1 (vertical) out from the edges of the runway OFZ and inner-approach OFZ to a height of 150 feet above the established airport elevation.

Inoperative components

Higher minimums are prescribed when the specified visual aids are not functioning; this information is listed in the Inoperative Components Table found in the United States Terminal Procedures Publications.

INS

Inertial Navigation System.

Insight

The grouping of perceptions into meaningful wholes. Creating insight is one of the instructor’s major responsibilities.

Insolation

Incoming solar radiation falling upon the earth and its atmosphere.

Instability

A general term to indicate various states of the atmosphere in which spontaneous convection will occur when prescribed criteria are met; indicative of turbulence. Types include: absolute instability, conditionally unstable air, convective instability.

Instantaneous vertical speed indicator (IVSI)

Assists in interpretation by instantaneously indicating the rate of climb or descent at a given moment with little or no lag as displayed in a vertical speed indicator (VSI).

Instantaneous vertical speed indicator (IVSI)

Assists in interpretation by instantaneously indicating the rate of climb or descent at a given moment with little or no lag as displayed in a vertical speed indicator (VSI).

Instructional aids

Devices that assist an instructor in the teaching-learning process. They are supplementary training devices, and are not self-supporting.

Instrument

A device using an internal mechanism to show visually or aurally the attitude, altitude, or operation of an aircraft or aircraft part. It includes electronic devices for automatically controlling an aircraft in flight.

Instrument Approach

Instrument Approach Procedure.

Instrument approach procedure (IAP)

A series of predetermined maneuvers by reference to flight instruments with specified protection from obstacles and assurance of navigation signal reception capability. It begins from the initial approach fix, or where applicable, from the beginning of a defined arrival route to a point:
(1) From which a landing can be completed; or
(2) If a landing is not completed, to a position at which holding or en route obstacle clearance criteria apply.

Instrument approach procedures (IAP)

A series of predetermined maneuvers for the orderly transfer of an aircraft under IFR from the beginning of the initial approach to a landing or to a point from which a landing may be made visually.

Instrument Approach Procedures (IAP) Charts

Portray the aeronautical data which is required to execute an instrument approach to an airport. These charts depict the procedures, including all related data, and the airport diagram. Each procedure is designated for use with a specific type of electronic navigation system including NDB, TACAN, VOR, ILS/MLS, and RNAV. These charts are identified by the type of navigational aid(s) which provide final approach guidance.

Instrument Approach Waypoint

Fixes used in defining RNAV IAPs, including the feeder waypoint (FWP), the initial approach waypoint (IAWP), the intermediate waypoint (IWP), the final approach waypoint (FAWP), the RWY WP, and the APT WP, when required.

Instrument Departure Procedure (DP)

A preplanned instrument flight rule (IFR) departure procedure published for pilot use, in graphic or textual format, that provides obstruction clearance from the terminal area to the appropriate en route structure. There are two types of DP, Obstacle Departure Procedure (ODP), printed either textually or graphically, and, Standard Instrument Departure (SID), which is always printed graphically.

Instrument Departure Procedure (DP) Charts

Designed to expedite clearance delivery and to facilitate transition between takeoff and en route operations. Each DP is presented as a separate chart and may serve a single airport or more than one airport in a given geographical location.

Instrument flight rules (IFR)

Rules and regulations established by the Federal Aviation Administration to govern flight under conditions in which flight by outside visual reference is not safe. IFR flight depends upon flying by reference to instruments in the flight deck, and navigation is accomplished by reference to electronic signals.

Instrument flight rules (IFR)

Instrument Landing System (ILS)

A precision instrument approach system that normally consists of the following electronic components and visual aids; localizer, glide slope, outer marker, middle marker, and approach lights.

Instrument landing system (ILS)

An electronic system that provides both horizontal and vertical guidance to a specific runway, used to execute a precision instrument approach procedure.

Instrument meteorological conditions (IMC)

Meteorological conditions expressed in terms of visibility, distance from clouds, and ceiling less than the minimums specified for visual meteorological conditions, requiring operations to be conducted under IFR.

Instrument meteorological conditions (IMC).

Instrument Procedure with Vertical Guidance (IPV)

Satellite or Flight Management System (FMS) lateral navigation (LNAV) with computed positive vertical guidance based on barometric or satellite elevation. This term has been renamed APV.

Instrument proficiency check

An evaluation ride based on the instrument rating practical test standard which is required to regain instrument flying privileges when the privileges have expired due to lack of currency.

Instrument Runway

A runway equipped with electronic and visual navigation aids for which a precision or nonprecision approach procedure having straight-in landing minimums has been approved.

Instrument takeoff

Using the instruments rather than outside visual cues to maintain runway heading and execute a safe takeoff.

INT

Intersection.

Integral Fuel Tank

A portion of the aircraft structure, usually a wing, which is sealed off and used as a fuel tank. When a wing is used as an integral fuel tank, it is called a “wet wing.”

Integrated flight instruction

A technique of flight instruction in which students are taught to perform flight maneuvers by reference to both the flight instruments and to outside visual references from the time the maneuver is first introduced. Handling of the controls is the same regardless of whether flight instruments or outside references are being used.

Integrity

The ability of a system to provide timely warnings to users when the system should not be used for navigation.

Intensity

A principle of learning in which a dramatic or exciting learning experience is likely to be remembered longer than a boring experience. Students experiencing the real thing will learn more than when they are merely told about the real thing.

Intercooler

A device used to reduce the temperature of the compressed air before it enters the fuel metering device. The resulting cooler air has a higher density, which permits the engine to be operated with a higher power setting.

Interference

(1) A theory of forgetting proposing that a person forgets something because a certain experience overshadows it, or the learning of similar things has intervened. (2) Barriers to effective communication that are caused by physiological, environmental, and psychological factors outside the direct control of the instructor. The instructor must take these factors into account in order to communicate effectively.

Interference drag

Drag generated by the collision of airstreams creating eddy currents, turbulence, or restrictions to smooth flow.

Interference drag

Drag generated by the collision of airstreams creating eddy currents, turbulence, or restrictions to smooth flow.

Intermediate Approach

The segment between the intermediate fix or point and the final approach fix.

Intermediate Approach Segment

Segments Of An Instrument Approach Procedure.

Intermediate Fix

The fix that identifies the beginning of the intermediate approach segment of an instrument approach procedure. The fix is not normally identified on the instrument approach chart as an intermediate fix (IF).

Internal Combustion Engines

An engine that produces power as a result of expanding hot gases from the combustion of fuel and air within the engine itself. A steam engine where coal is burned to heat up water inside the engine is an example of an external combustion engine.

International Airport

Relating to international flight, it means: a. An airport of entry which has been designated by the Secretary of Treasury or Commissioner of Customs as an international airport for customs service. b. A landing rights airport at which specific permission to land must be obtained from customs authorities in advance of contemplated use. c. Airports designated under the Convention on International Civil Aviation as an airport for use by international commercial air transport and/or international general aviation.

International Civil Aviation Organization (ICAO)

ICAO is a specialized agency of the United Nations whose objective is to develop standard principles and techniques of international air navigation and to promote development of civil aviation.

International Civil Aviation Organization [ICAO]

A specialized agency of the United Nations whose objective is to develop the principles and techniques of international air navigation and to foster planning and development of international civil air transport. Regions include: 1. African-Indian Ocean Region 2. Caribbean Region 3. European Region 4. Middle East/Asia Region 5. North American Region 6. North Atlantic Region 7. Pacific Region 8. South American Region

International Flight Information Manual

A publication designed primarily as a pilot’s preflight planning guide for flights into foreign airspace and for flights returning to the U.S. from foreign locations.

International standard atmosphere (IAS)

A model of standard variation of pressure and temperature.

International standard atmosphere (IAS)

A model of standard variation of pressure and temperature.

Interpolate

To determine a value in a series between two known values.

Interpolation

The estimation of an intermediate value of a quantity that falls between marked values in a series. Example: In a measurement of length, with a rule that is marked in eighths of an inch, the value falls between 3/8 inch and 1/2 inch. The estimated (interpolated) value might then be said to be 7/16 inch.

Interrogator

The ground-based surveillance radar beacon transmitter-receiver, which normally scans in synchronism with a primary radar, transmitting discrete radio signals which repetitiously request all transponders on the mode being used to reply. The replies received are mixed with the primary radar returns and displayed on the same plan position indicator (radar scope). Also, applied to the airborne element of the TACAN/DME system.

Intersecting Runways

Two or more runways which cross or meet within their lengths.

Intersection

A. A point defined by any combination of courses, radials, or bearings of two or more navigational aids.
B. Used to describe the point where two runways, a runway and a taxiway, or two taxiways cross or meet.

Intersection Departure

A departure from any runway intersection except the end of the runway.

Intersection Takeoff

Intersection Departure.

Interstage Turbine Temperature (ITT)

The temperature of the gases between the high pressure and low pressure turbines.

Interstate air commerce

The carriage by aircraft of persons or property for compensation or hire, or the carriage of mail by aircraft, or the operation or navigation of aircraft in the conduct or furtherance of a business or vocation, in commerce between a place in any State of the United States, or the District of Columbia, and a place in any other State of the United States, or the District of Columbia; or between places in the same State of the United States through the airspace over any place outside thereof; or between places in the same territory or possession of the United States, or the District of Columbia.

Interstate air transportation

The carriage by aircraft of persons or property as a common carrier for compensation or hire, or the carriage of mail by aircraft in commerce:
(1) Between a place in a State or the District of Columbia and another place in another State or the District of Columbia;
(2) Between places in the same State through the airspace over any place outside that State; or
(3) Between places in the same possession of the United States;
Whether that commerce moves wholly by aircraft of partly by aircraft and partly by other forms of transportation.

Intertropical convergence zone

The boundary zone between the trade wind system of the Northern and Southern Hemispheres; it is characterized in maritime climates by showery precipitation with cumulonimbus clouds sometimes extending to great heights.

Into A.C

Current of the proper voltage and frequency to operate A.C. gyro instruments.

Intrastate air transportation

The carriage of persons or property as a common carrier for compensation or hire, by turbojet-powered aircraft capable of carrying thirty or more persons, wholly within the same State of the United States.

Inversion

An increase in temperature with height-a reversal of the normal decrease with height in the troposphere; may also be applied to other meteorological properties.

Inversion

An increase in temperature with altitude.

Inversion illusion

The feeling that the aircraft is tumbling backwards, caused by an abrupt change from climb to straight- and-level flight while in situations lacking visual reference.

Inversion illusion

The feeling that the aircraft is tumbling backwards, caused by an abrupt change from climb to straight-and-level flight while in situations lacking visual reference.

Inverter

An electrical device that changes DC to AC power.

IPV

Instrument Procedure With Vertical Guidance (This term has been renamed APV)

IR

IFR Military Training Route

IRU

Inertial Reference Unit

ISA (International Standard Atmosphere)

Standard atmospheric conditions consisting of a temperature of 59°F (15°C), and a barometric pressure of 29.92 in. Hg. (1013.2 mb) at sea level. ISA values can be calculated for various altitudes using a standard lapse rate of approximately 2°C per 1,000 feet.

Iso echo

In radar circuitry, a circuit that reverses signal strength above a specified intensity level, thus causing a void on the scope in the most intense portion of an echo when maximum intensity is greater than the specified level.

Isobar

A line of equal or constant barometric pressure.

Isobars

Lines which connect points of equal barometric pressure.

Isogonic lines

Lines drawn across aeronautical charts to connect points having the same magnetic variation.

Isogonic lines

Lines drawn across aeronautical charts to connect points having the same magnetic variation.

Isoheight

On a weather chart, a line of equal height; same as contour (1).

Isoline

A line of equal value of a variable quantity, i.e., an isoline of temperature is an isotherm, etc. Isobars (A line of equal or constant barometric pressure.) and isotachs (A line of equal or constant wind speed.) are examples.

Isoshear

A line of equal wind shear.

Isotach

A line of equal or constant wind speed.

Isotherm

A line of equal or constant temperature.

Isothermal

Of equal or constant temperature, with respect to either space or time; more commonly, temperature with height; a zero lapse rate.

IVSI

Instantaneous Vertical Speed Indicator.

IVSI

Instantaneous Vertical Speed Indicator.

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