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 and performance. A method of attitude instrument
flying in which one instrument is used for making attitude
changes, and the other instruments are used to monitor the
progress of the change.
Control display unit. A display interfaced with the master
computer, providing the pilot with a single control point
for all navigations 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. It includes
Class A, Class B, Class C, Class D, and Class E airspace.
Control pressures. The amount of physical exertion on the
control column necessary to achieve the desired attitude.
Convective weather. Unstable, rising air found in
cumiliform clouds.
Convective SIGMET. Weather advisory concerning
convective weather significant to the safety of all aircraft,
including thunderstorms, hail, and tornadoes.
Coordinated flight. Flight with a minimum disturbance of
the forces maintaining equilibrium, established via effective
control use.
COP. See changeover point.
Coriolis illusion. The illusion of rotation or movement in an
entirely different axis, caused by an abrupt head movement,
while in a prolonged constant rate turn that has ceased
stimulating the brain’s motion sensing system.
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 localizer or glide slope antennas.
CRM. See crew resource management.
Cross-check. The first fundamental skill of instrument flight,
also known as “scan,” the continuous and logical observation
of instruments for attitude and performance information.
Cruise clearance. An ATC clearance issued to allow a
pilot to conduct flight at any altitude from the minimum
IFR altitude up to and including the altitude specified in the
clearance. Also authorizes a pilot 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.
DA. See decision altitude.
D.C. Direct current.
Dark adaptation. 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 compass card to rotate
toward South.
Decision altitude (DA). A specified altitude in the precision
approach, charted in feet 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 the precision
approach, charted in height above threshold elevation,
at which a decision must be made either to continue the
approach or to execute a missed approach.
Deice. The act of removing ice accumulation from an
aircraft structure.
Density altitude. Pressure altitude corrected for nonstandard
temperature. Density altitude is used in computing the
performance of an aircraft and its engines.
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. Deviation error is different
on each heading.
DGPS. Differential global positioning system.
DH. See decision height.
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 attitude 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 access to the system. Pilots can request
specific types of weather briefings and other pertinent data
for planned flights.
Distance circle. See reference circle.
Distance measuring equipment (DME). A pulse-type
electronic navigation system that shows the pilot, by an
instrument-panel indication, the number of nautical miles
between the aircraft and a ground station or waypoint.
DME. See distance measuring equipment.
DME arc. A flight track that is a constant distance from the
station or waypoint.
DOD. Department of Defense.
Doghouse. A turn-and-slip indicator dial mark in the shape
of a doghouse.
Domestic Reduced Vertical Separation Minimum
(DRVSM). Additional flight levels between FL 290 and FL
410 to provide operational, traffic, and airspace efficiency.
Double gimbal. A type of mount used for the gyro in an
attitude instrument. The axes of the two gimbals are at right
angles to the spin axis of the gyro, allowing free motion in
two planes around the gyro.
DP. See departure procedure.
Drag. The net aerodynamic force parallel to the relative
wind, usually the sum of two components: induced drag
and parasite drag.
Drag curve. The curve created when plotting induced drag
and parasite drag.
DUATS. See direct user access terminal system.
Duplex. Transmitting on one frequency and receiving on a
separate frequency.
Eddy currents. Current induced in a metal cup or disc when
it is crossed by lines of flux from a moving magnet.
EFAS. See En Route Flight Advisory Service.
EFC. See expect-further-clearance.
Electronic flight display (EFD). For the purpose of
standardization, any flight instrument display that uses
LCD or other image-producing system (Cathode Ray Tube
[CRT], etc.)
Elevator illusion. The sensation of being in a climb or
descent, caused by the kind of abrupt vertical accelerations
that result from up- or downdrafts.
Emergency. A distress or urgent condition.
Emphasis error. The result of giving too much attention
to a particular instrument during the cross-check, instead of
relying on a combination of instruments necessary for attitude
and performance information.
EM wave. Electromagnetic wave.
Encoding altimeter. A special type of pressure altimeter
used to send a signal to the air traffic controller on the ground,
showing the pressure altitude the aircraft is flying.
En route facilities ring. Depicted in the plan view of IAP
charts, a circle which designates NAVAIDs, fixes, and
intersections that are part of the en route low altitude airway
structure.
En Route Flight Advisory Service (EFAS). An en route
weather-only AFSS service.
En route high-altitude charts. Aeronautical charts for en
route instrument navigation at or above 18,000 feet MSL.
En route low-altitude charts. Aeronautical charts for en
route IFR navigation below 18,000 feet MSL.
Equivalent airspeed. Airspeed equivalent to CAS in
standard atmosphere at sea level. As the airspeed and pressure
altitude increase, the CAS becomes higher than it should be,
and a correction for compression must be subtracted from
the CAS.
Expect-further-clearance (EFC). The time a pilot can
expect to receive clearance beyond a clearance limit.
FAA. Federal Aviation Administration.
FAF. See final approach fix.
False horizon. Inaccurate visual information for aligning the
aircraft, caused by various natural and geometric formations
that disorient the pilot from the actual horizon.
Federal airways. Class E airspace areas that extend upward
from 1,200 feet to, but not including, 18,000 feet MSL, unless
otherwise specified.
Feeder facilities. Used by ATC to direct aircraft to
intervening fixes between the en route structure and the
initial approach fix.
Final approach. Part of an instrument approach
procedure in which alignment and descent for landing are
accomplished.
Final approach fix (FAF). The fix from which the IFR
final approach to an airport is executed, and which identifies
the beginning of the final approach segment. An FAF is
designated on government charts by a Maltese cross symbol
for nonprecision approaches, and a lightning bolt symbol for
precision approaches.
Fixating. Staring at a single instrument, thereby interrupting
the cross-check process.
FL. See flight level.
Flight configurations. Adjusting the aircraft control surfaces
(including flaps and landing gear) in a manner that will
achieve a specified attitude.
Flight director indicator (FDI). One of the major components
of a flight director system, it provides steering commands that
the pilot (or the autopilot, if coupled) follows.
Flight level (FL). A measure of altitude (in hundreds of feet)
used by aircraft flying above 18,000 feet with the altimeter
set at 29.92" Hg.
Flight management system (FMS). Provides pilot and crew
with highly accurate and automatic long-range navigation
capability, blending available inputs from long- and short-
range sensors.
Flightpath. The line, course, or track along which an aircraft
is flying or is intended to be flown.
Flight patterns. Basic maneuvers, flown by reference to the
instruments rather than outside visual cues, for the purpose
of practicing basic attitude flying. The patterns simulate
maneuvers encountered on instrument flights such as holding
patterns, procedure turns, and approaches.
Flight strips. Paper strips containing instrument flight
information, used by ATC when processing flight plans.
FMS. See flight management system.
Form drag. The drag created because of the shape of a
component or the aircraft.
Fundamental skills. Pilot skills of instrument cross-check,
instrument interpretation, and aircraft control.
Glideslope (GS). Part of the ILS that projects a radio beam
upward at an angle of approximately 3° from the approach
end of an instrument runway. The glideslope provides
vertical guidance to aircraft on the final approach course for
the aircraft to follow when making an ILS approach along
the localizer path.
Glideslope intercept altitude. The minimum altitude of an
intermediate approach segment prescribed for a precision
approach that ensures obstacle clearance.
Global landing system (GLS). An instrument approach with
lateral and vertical guidance with integrity limits (similar to
barometric vertical navigation (BRO VNAV).
Global navigation satellite systems (GNSS). Satellite
navigation systems that provide autonomous geo-spatial
positioning with global coverage. It allows small electronic
receivers to determine their location (longitude, latitude, and
altitude) to within a few meters using time signals transmitted
along a line of sight by radio from satellites.
GNSS. See global navigation satellite systems.
Global positioning system (GPS). Navigation system
that uses satellite rather than ground-based transmitters for
location information.
Goniometer. As used in radio frequency (RF) antenna
systems, a direction-sensing device consisting of two fixed
loops of wire oriented 90° from each other, which separately
sense received signal strength and send those signals to two
rotors (also oriented 90°) in the sealed direction-indicating
instrument. The rotors are attached to the direction-indicating
needle of the instrument and rotated by a small motor until
minimum magnetic field is sensed near the rotors.
GPS. See global positioning system.
GPS Approach Overlay Program. An authorization for
pilots to use GPS avionics under IFR for flying designated
existing nonprecision instrument approach procedures, with
the exception of LOC, LDA, and SDF procedures.
Graveyard spiral. The illusion of the cessation of a turn
while still in a prolonged, coordinated, constant rate turn,
which can lead a disoriented pilot to a loss of control of the
aircraft.
Great circle route. The shortest distance across the surface
of a sphere (the Earth) between two points on the surface.
Ground proximity warning system (GPWS). A system
designed to determine an aircraft’s clearance above the Earth
and provides limited predictability about aircraft position
relative to rising terrain.
Groundspeed. Speed over the ground, either closing speed to
the station or waypoint, or speed over the ground in whatever
direction the aircraft is going at the moment, depending upon
the navigation system used.
GS. See glide slope.
GWPS. See ground proximity warning system.
HAA. See height above airport.
HAL. See height above landing.
HAT. See height above touchdown elevation.
Hazardous attitudes. Five aeronautical decision-making
attitudes that may contribute to poor pilot judgment:
antiauthority, impulsivity, invulnerability, machismo, and
resignation.
Hazardous Inflight Weather Advisory Service (HIWAS).
Service providing recorded weather forecasts broadcast to
airborne pilots over selected VORs.
Head-up display (HUD). A special type of flight viewing
screen that allows the pilot to watch the flight instruments
and other data while looking through the windshield of the
aircraft for other traffic, the approach lights, or the runway.
Height above airport (HAA). The height of the MDA above
the published airport elevation.
Height above landing (HAL). The height above a designated
helicopter landing area used for helicopter instrument
approach procedures.
Height above touchdown elevation (HAT). The DA/DH or
MDA above the highest runway elevation in the touchdown
zone (first 3,000 feet of the runway).
HF. High frequency.
Hg. Abbreviation for mercury, from the Latin
hydrargyrum.
HIWAS. See Hazardous Inflight Weather Advisory
Service.
Holding. A predetermined maneuver that keeps aircraft
within a specified airspace while awaiting further clearance
from ATC.
Holding pattern. A racetrack pattern, involving two turns
and two legs, used to keep an aircraft within a prescribed
airspace with respect to a geographic fix. A standard pattern
uses right turns; nonstandard patterns use left turns.
Homing. Flying the aircraft on any heading required to keep
the needle pointing to the 0° relative bearing position.
Horizontal situation indicator (HSI). A flight navigation
instrument that combines the heading indicator with a CDI,
in order to provide the pilot with better situational awareness
of location with respect to the courseline.
HSI. See horizontal situation indicator.
HUD. See head-up display.
Human factors. A multidisciplinary field encompassing the
behavioral and social sciences, engineering, and physiology,
to consider the variables that influence individual and
crew performance for the purpose of optimizing human
performance and reducing errors.
Hypoxia. A state of oxygen deficiency in the body sufficient
to impair functions of the brain and other organs.
IAF. See initial approach fix.
IAP. See instrument approach procedures.
IAS. See indicated airspeed.
ICAO. See International Civil Aviation Organization.
Ident. Air Traffic Control request for a pilot to push
the button on the transponder to identify return on the
controller’s scope.
IFR. See instrument flight rules.
ILS. See instrument landing system.
ILS categories. Categories of instrument approach
procedures allowed at airports equipped with the following
types of instrument landing systems:
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.
IMC. See instrument meteorological conditions.
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.
Indirect indication. A reflection of aircraft pitch-and-bank
attitude by the instruments other than the attitude indicator.
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.
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.
Initial approach fix (IAF). The fix depicted on IAP charts
where the instrument approach procedure (IAP) begins unless
otherwise authorized by ATC.
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. See inertial navigation system.
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).
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 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 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 takeoff. Using the instruments rather than
outside visual cues to maintain runway heading and execute
a safe takeoff.
Interference drag. Drag generated by the collision of
airstreams creating eddy currents, turbulence, or restrictions
to smooth flow.
International Civil Aviation Organization (ICAO). The
United Nations agency for developing the principles and
techniques of international air navigation, and fostering planning
and development of international civil air transport.
International standard atmosphere (IAS). A model of
standard variation of pressure and temperature.
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. A solid-state electronic device that converts D.C.
into A.C. current of the proper voltage and frequency to
operate A.C. gyro instruments.
Isogonic lines. Lines drawn across aeronautical charts to
connect points having the same magnetic variation.
IVSI. See instantaneous vertical speed indicator.
Jet route. A route designated to serve flight operations from
18,000 feet MSL up to and including FL 450.
Jet stream. A high-velocity narrow stream of winds, usually
found near the upper limit of the troposphere, which flows
generally from west to east.
KIAS. Knots indicated airspeed.
Kollsman window. A barometric scale window of a
sensitive altimeter used to adjust the altitude for the
altimeter setting.
LAAS. See local area augmentation system.
Lag. The delay that occurs before an instrument needle attains
a stable indication.
Land as soon as possible. ATC instruction to pilot. Land
without delay at the nearest suitable area, such as an open
field, at which a safe approach and landing is assured.
Land as soon as practical. ATC instruction to pilot. The
landing site and duration of flight are at the discretion of the
pilot. Extended flight beyond the nearest approved landing
area is not recommended.
Land immediately. ATC instruction to pilot. The urgency
of the landing is paramount. The primary consideration is
to ensure the survival of the occupants. Landing in trees,
water, or other unsafe areas should be considered only as
a last resort.
LDA. See localizer-type directional aid.
Lead radial. The radial at which the turn from the DME arc
to the inbound course is started.
Leans, the. A physical sensation caused by an abrupt
correction of a banked attitude entered too slowly to
stimulate the motion sensing system in the inner ear. The
abrupt correction can create the illusion of banking in the
opposite direction.
Lift. A component of the total aerodynamic force on an airfoil
and acts perpendicular to the relative wind.
Lines of flux. Invisible lines of magnetic force passing
between the poles of a magnet.
L/MF. See low or medium frequency.
LMM. See locator middle marker.
Load factor. The ratio of a specified load to the total weight
of the aircraft. The specified load is expressed in terms of
any of the following: aerodynamic forces, inertial forces, or
ground or water reactions.
Loadmeter. A type of ammeter installed between the generator
output and the main bus in an aircraft electrical system.
LOC. See localizer.
Local area augmentation system (LAAS). A differential
global positioning system (DGPS) that improves the accuracy
of the system by determining position error from the GPS
satellites, then transmitting the error, or corrective factors,
to the airborne GPS receiver.
Localizer (LOC). The portion of an ILS that gives left/right
guidance information down the centerline of the instrument
runway for final approach.
Localizer-type directional aid (LDA). A NAVAID used
for nonprecision instrument approaches with utility and
accuracy comparable to a localizer but which is not a part
of a complete ILS and is not aligned with the runway. Some
LDAs are equipped with a glide slope.
Locator middle marker (LMM). Nondirectional radio
beacon (NDB) compass locator, collocated with a middle
marker (MM).
Locator outer marker (LOM). NDB compass locator,
collocated with an outer marker (OM).
LOM. See locator outer marker.
Long range navigation (LORAN). An electronic
navigational system by which hyperbolic lines of position
are determined by measuring the difference in the time of
reception of synchronized pulse signals from two fixed
transmitters. LORAN A operates in the 1750 to 1950 kHz
frequency band. LORAN C and D operate in the 100 to 110
kHz frequency band.
LORAN. See long range navigation.
Low or medium frequency. A frequency range between
190–535 kHz with the medium frequency above 300
kHz. Generally associated with nondirectional beacons
transmitting a continuous carrier with either a 400 or 1,020
Hz modulation.
Lubber line. The reference line used in a magnetic compass
or heading indicator.
MAA. See maximum authorized altitude.
Mach number. The ratio of the true airspeed of the aircraft
to the speed of sound in the same atmospheric conditions,
named in honor of Ernst Mach, late 19th century physicist.
Mach meter. The instrument that displays the ratio of the
speed of sound to the true airspeed an aircraft is flying.
Magnetic bearing (MB). The direction to or from a radio
transmitting station measured relative to magnetic north.
Magnetic heading (MH). The direction an aircraft is pointed
with respect to magnetic north.
Mandatory altitude. An altitude depicted on an instrument
approach chart with the altitude value both underscored and
overscored. Aircraft are required to maintain altitude at the
depicted value.
Mandatory block altitude. An altitude depicted on an
instrument approach chart with two underscored and
overscored altitude values between which aircraft are
required to maintain altitude.
MAP. See missed approach point.
Margin identification. The top and bottom areas on an
instrument approach chart that depict information about
the procedure, including airport location and procedure
identification.
Marker beacon. A low-powered transmitter that directs its
signal upward in a small, fan-shaped pattern. Used along the
flight path when approaching an airport for landing, marker
beacons indicate both aurally and visually when the aircraft
is directly over the facility.
Maximum altitude. An altitude depicted on an instrument
approach chart with overscored altitude value at which or
below aircraft are required to maintain altitude.
Maximum authorized altitude (MAA). A published altitude
representing the maximum usable altitude or flight level for
an airspace structure or route segment.
MB. See magnetic bearing.
MCA. See minimum crossing altitude.
MDA. See minimum descent altitude.
MEA. See minimum en route altitude.
Mean sea level. The average height of the surface of the
sea at a particular location for all stages of the tide over a
19-year period.
MFD. See multi-function display.
MH. See magnetic heading.
MHz. Megahertz.
Microwave landing system (MLS). A precision instrument
approach system operating in the microwave spectrum which
normally consists of an azimuth station, elevation station,
and precision distance measuring equipment.
Mileage breakdown. A fix indicating a course change
that appears on the chart as an “x” at a break between two
segments of a federal airway.
Military operations area (MOA). Airspace established for
the purpose of separating certain military training activities
from IFR traffic.
Military training route (MTR). Airspace of defined vertical
and lateral dimensions established for the conduct of military
training at airspeeds in excess of 250 knots indicated airspeed
(KIAS).
Minimum altitude. An altitude depicted on an instrument
approach chart with the altitude value underscored. Aircraft are
required to maintain altitude at or above the depicted value.
Minimum crossing altitude (MCA). The lowest allowed
altitude at certain fixes an aircraft must cross when proceeding
in the direction of a higher minimum en route altitude
(MEA).
Minimum descent altitude (MDA). The lowest altitude (in
feet MSL) to which descent is authorized on final approach,
or during circle-to-land maneuvering in execution of a
nonprecision approach.
Minimum en route altitude (MEA). The lowest published
altitude between radio fixes that ensures acceptable
navigational signal coverage and meets obstacle clearance
requirements between those fixes.
Minimum obstruction clearance altitude (MOCA). The
lowest published altitude in effect between radio fixes on VOR
airways, off-airway routes, or route segments, which meets
obstacle clearance requirements for the entire route segment
and which ensures acceptable navigational signal coverage
only within 25 statute (22 nautical) miles of a VOR.
Minimum reception altitude (MRA). The lowest altitude
at which an airway intersection can be determined.
Minimum safe altitude (MSA). The minimum altitude
depicted on approach charts which provides at least 1,000 feet
of obstacle clearance for emergency use within a specified
distance from the listed navigation facility.
Minimum vectoring altitude (MVA). An IFR altitude lower
than the minimum en route altitude (MEA) that provides
terrain and obstacle clearance.
Minimums section. The area on an IAP chart that displays the
lowest altitude and visibility requirements for the approach.
Missed approach. A maneuver conducted by a pilot when an
instrument approach cannot be completed to a landing.
Missed approach point (MAP). A point prescribed in each
instrument approach at which a missed approach procedure
shall be executed if the required visual reference has not
been established.
Mixed ice. A mixture of clear ice and rime ice.
MLS. See microwave landing system.
MM. Middle marker.
MOA. See military operations area.
MOCA. See minimum obstruction clearance altitude.
Mode C. Altitude reporting transponder mode.
MRA. See minimum reception altitude.
MSA. See minimum safe altitude.
MSL. See mean sea level.
MTR. See military training route.
Multi-function display (MFD). Small screen (CRT or LCD)
in an aircraft that can be used to display information to the
pilot in numerous configurable ways. Often an MFD will be
used in concert with a Primary Flight Display.
MVA. See minimum vectoring altitude.
NACG. See National Aeronautical Charting Group.
NAS. See National Airspace System.
National Airspace System (NAS). The common network of
United States airspace—air navigation facilities, equipment
and services, airports or landing areas; aeronautical charts,
information and services; rules, regulations and procedures,
technical information; and manpower and material.