G-16
Indirect indication. A reflection of aircraft pitch-and-bank
attitude by 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.
Intercooler. A device used to reduce the temperatures 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 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.
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.
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.
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.
Isobars. Lines which connect points of equal barometric
pressure.
Isogonic lines. Lines drawn across aeronautical charts to
connect points having the same magnetic variation.
IVSI. See instantaneous vertical speed indicator.
G-17
J
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.
Judgment. The mental process of recognizing and analyzing
all pertinent information in a particular situation, a rational
evaluation of alternative actions in response to it, and a timely
decision on which action to take.
K
KIAS. Knots indicated airspeed.
Knot. The knot is a unit of speed equal to one nautical mile
(1.852 km) per hour, approximately 1.151 mph.
Kollsman window. A barometric scale window of a
sensitive altimeter used to adjust the altitude for the
altimeter setting.
L
LAAS. See local area augmentation system.
Lag. The delay that occurs before an instrument needle attains
a stable indication.
Land breeze. A coastal breeze flowing from land to sea
caused by temperature differences when the sea surface is
warmer than the adjacent land. The land breeze usually occurs
at night and alternates with the sea breeze that blows in the
opposite direction by day.
Land as soon as possible. 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. 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. 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.
Lateral axis. An imaginary line passing through the center
of gravity of an airplane and extending across the airplane
from wingtip to wingtip.
Lateral stability (rolling). The stability about the
longitudinal axis of an aircraft. Rolling stability or the ability
of an airplane to return to level flight due to a disturbance
that causes one of the wings to drop.
Latitude. Measurement north or south of the equator in
degrees, minutes, and seconds. Lines of latitude are also
referred to as parallels.
LDA. See localizer-type directional aid.
Lead radial. The radial at which the turn from the DME arc
to the inbound course is started.
Leading edge. The part of an airfoil that meets the airflow first.
Leading edge devices. High lift devices which are found
on the leading edge of the airfoil. The most common types
are fixed slots, movable slats, and leading edge flaps.
Leading-edge flap. A portion of the leading edge of an
airplane wing that folds downward to increase the camber,
lift, and drag of the wing. The leading-edge flaps are
extended for takeoffs and landings to increase the amount
of aerodynamic lift that is produced at any given airspeed.
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.
Licensed empty weight. The empty weight that consists
of the airframe, engine(s), unusable fuel, and undrainable
oil plus standard and optional equipment as specified in the
equipment list. Some manufacturers used this term prior to
GAMA standardization.
Lift. A component of the total aerodynamic force on an airfoil
and acts perpendicular to the relative wind.
Limit load factor. Amount of stress, or load factor, that an
aircraft can withstand before structural damage or failure
occurs.
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.
G-18
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 glideslope.
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.
Longitude. Measurement east or west of the Prime Meridian
in degrees, minutes, and seconds. The Prime Meridian is 0°
longitude and runs through Greenwich, England. Lines of
longitude are also referred to as meridians.
Longitudinal axis. An imaginary line through an aircraft
from nose to tail, passing through its center of gravity. The
longitudinal axis is also called the roll axis of the aircraft.
Movement of the ailerons rotates an airplane about its
longitudinal axis.
Longitudinal stability (pitching). Stability about the lateral
axis. A desirable characteristic of an airplane whereby it tends
to return to its trimmed angle of attack after displacement.
Low or medium frequency. A frequency range between
190 and 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.
M
MAA. See maximum authorized altitude.
MAC. See mean aerodynamic chord.
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 compass. A device for determining direction
measured from magnetic north.
Magnetic dip. A vertical attraction between a compass
needle and the magnetic poles. The closer the aircraft is to a
pole, the more severe the effect.
Magnetic heading (MH). The direction an aircraft is pointed
with respect to magnetic north.
Magneto. A self-contained, engine-driven unit that supplies
electrical current to the spark plugs; completely independent
of the airplane’s electrical system. Normally there are two
magnetos per engine.
Magnus effect. Lifting force produced when a rotating
cylinder produces a pressure differential. This is the same
effect that makes a baseball curve or a golf ball slice.
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.
G-19
Maneuverability. Ability of an aircraft to change directions
along a flight path and withstand the stresses imposed upon it.
Maneuvering speed (VA). The design maneuvering speed.
Operating at or below design maneuvering speed does not
provide structural protection against multiple full control
inputs in one axis or full control inputs in more than one
axis at the same time.
Manifold absolute pressure. The absolute pressure of the
fuel/air mixture within the intake manifold, usually indicated
in inches of mercury.
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.
Mass. The amount of matter in a body.
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.
Maximum landing weight. The greatest weight that an
airplane normally is allowed to have at landing.
Maximum ramp weight. The total weight of a loaded aircraft,
including all fuel. It is greater than the takeoff weight due to the
fuel that will be burned during the taxi and runup operations.
Ramp weight may also be referred to as taxi weight.
Maximum takeoff weight. The maximum allowable weight
for takeoff.
Maximum weight. The maximum authorized weight of
the aircraft and all of its equipment as specified in the Type
Certificate Data Sheets (TCDS) for the aircraft.
Maximum zero fuel weight (GAMA). The maximum
weight, exclusive of usable fuel.
MB. See magnetic bearing.
MCA. See minimum crossing altitude.
MDA. See minimum descent altitude.
MEA. See minimum en route altitude.
Mean aerodynamic chord (MAC). The average distance
from the leading edge to the trailing edge of the wing.
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.
MEL. See minimum equipment list.
Meridians. Lines of longitude.
Mesophere. A layer of the atmosphere directly above the
stratosphere.
METAR. See Aviation Routine Weather Report.
MFD. See multi-function display.
MH. See magnetic heading.
MHz. Megahertz.
Microburts. A strong downdraft which normally occurs
over horizontal distances of 1 NM or less and vertical
distances of less than 1,000 feet. In spite of its small
horizontal scale, an intense microburst could induce
windspeeds greater than 100 knots and downdrafts as strong
as 6,000 feet per minute.
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.
G-20
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 drag. The point on the total drag curve where
the lift-to-drag ratio is the greatest. At this speed, total drag
is minimized.
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 equipment list (MEL). A list developed for larger
aircraft that outlines equipment that can be inoperative for
various types of flight including IFR and icing conditions. This
list is based on the master minimum equipment list (MMEL)
developed by the FAA and must be approved by the FAA for
use. It is specific to an individual aircraft make and model.
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.
Moment. The product of the weight of an item multiplied
by its arm. Moments are expressed in pound-inches (lb-in).
Total moment is the weight of the airplane multiplied by the
distance between the datum and the CG.
Moment arm. The distance from a datum to the applied force.
Moment index (or index). A moment divided by a constant
such as 100, 1,000, or 10,000. The purpose of using a moment
index is to simplify weight and balance computations of
airplanes where heavy items and long arms result in large,
unmanageable numbers.
Monocoque. A shell-like fuselage design in which the
stressed outer skin is used to support the majority of imposed
stresses. Monocoque fuselage design may include bulkheads
but not stringers.
Monoplanes. Airplanes with a single set of wings.
Movable slat. A movable auxiliary airfoil on the leading edge
of a wing. It is closed in normal flight but extends at high
angles of attack. This allows air to continue flowing over the
top of the wing and delays airflow separation.
MRA. See minimum reception altitude.
MSA. See minimum safe altitude.
MSL. See mean sea level.
G-21
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.
N
N1. Rotational speed of the low pressure compressor in a
turbine engine.
N2. Rotational speed of the high pressure compressor in a
turbine engine.
Nacelle. A streamlined enclosure on an aircraft in which
an engine is mounted. On multiengine propeller-driven
airplanes, the nacelle is normally mounted on the leading
edge of the wing.
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.
National Aeronautical Charting Group (NACG). A
Federal agency operating under the FAA, responsible for
publishing charts such as the terminal procedures and en
route charts.
National Route Program (NRP). A set of rules and
procedures designed to increase the flexibility of user flight
planning within published guidelines.
National Security Area (NSA). Areas consisting of airspace of
defined vertical and lateral dimensions established at locations
where there is a requirement for increased security and safety
of ground facilities. Pilots are requested to voluntarily avoid
flying through the depicted NSA. When it is necessary to
provide a greater level of security and safety, flight in NSAs
may be temporarily prohibited. Regulatory prohibitions are
disseminated via NOTAMs.
National Transportation Safety Board (NTSB). A United
States Government independent organization responsible for
investigations of accidents involving aviation, highways,
waterways, pipelines, and railroads in the United States.
NTSB is charged by congress to investigate every civil
aviation accident in the United States.
NAVAID. Navigational aid.
NAV/COM. Navigation and communication radio.
NDB. See nondirectional radio beacon.
Negative static stability. The initial tendency of an aircraft
to continue away from the original state of equilibrium after
being disturbed.
Neutral static stability. The initial tendency of an aircraft
to remain in a new condition after its equilibrium has been
disturbed.
NM. Nautical mile.
NOAA. National Oceanic and Atmospheric Administration.
No-gyro approach. A radar approach that may be used in
case of a malfunctioning gyro-compass or directional gyro.
Instead of providing the pilot with headings to be flown,
the controller observes the radar track and issues control
instructions “turn right/left” or “stop turn,” as appropriate.
Nondirectional radio beacon (NDB). A ground-based radio
transmitter that transmits radio energy in all directions.
Nonprecision approach. A standard instrument approach
procedure in which only horizontal guidance is provided.
No procedure turn (NoPT). Term used with the appropriate
course and altitude to denote that the procedure turn is not
required.
NoPT. See no procedure turn.
NOTAM. See Notice to Airmen.
Notice to Airmen (NOTAM). A notice filed with an aviation
authority to alert aircraft pilots of any hazards en route or at
a specific location. The authority in turn provides means of
disseminating relevant NOTAMs to pilots.
G-22
NRP. See National Route Program.
NSA. See National Security Area.
NTSB. See National Transportation Safety Board.
NWS. National Weather Service.
O
Obstacle departure procedures (ODP). A preplanned
instrument flight rule (IFR) departure procedure printed for
pilot use in textual or graphic form to provide obstruction
clearance via the least onerous route from the terminal area
to the appropriate en route structure. ODPs are recommended
for obstruction clearance and may be flown without ATC
clearance unless an alternate departure procedure (SID or
radar vector) has been specifically assigned by ATC.
Obstruction lights. Lights that can be found both on and off
an airport to identify obstructions.
Occluded front. A frontal occlusion occurs when a fast-
moving cold front catches up with a slow moving warm front.
The difference in temperature within each frontal system is
a major factor in determining whether a cold or warm front
occlusion occurs.
ODP. See obstacle departure procedures.
OM. Outer marker.
Omission error. The failure to anticipate significant
instrument indications following attitude changes; for
example, concentrating on pitch control while forgetting
about heading or roll information, resulting in erratic control
of heading and bank.
Optical illusion. A misleading visual image. For the
purpose of this handbook, the term refers to the brain’s
misinterpretation of features on the ground associated
with landing, which causes a pilot to misread the spatial
relationships between the aircraft and the runway.
Orientation. Awareness of the position of the aircraft and of
oneself in relation to a specific reference point.
Otolith organ. An inner ear organ that detects linear
acceleration and gravity orientation.
Outer marker. A marker beacon at or near the glideslope
intercept altitude of an ILS approach. It is normally located
four to seven miles from the runway threshold on the
extended centerline of the runway.
Outside air temperature (OAT). The measured or indicated
air temperature (IAT) corrected for compression and friction
heating. Also referred to as true air temperature.
Overcontrolling. Using more movement in the control
column than is necessary to achieve the desired pitch-and-
bank condition.
Overboost. A condition in which a reciprocating engine
has exceeded the maximum manifold pressure allowed by
the manufacturer. Can cause damage to engine components.
Overpower. To use more power than required for the purpose
of achieving a faster rate of airspeed change.
P
P-static. See precipitation static.
PAPI. See precision approach path indicator.
PAR. See precision approach radar.
Parallels. Lines of latitude.
Parasite drag. Drag caused by the friction of air moving
over the aircraft structure; its amount varies directly with
the airspeed.
Payload (GAMA). The weight of occupants, cargo, and
baggage.
Personality. The embodiment of personal traits and
characteristics of an individual that are set at a very early
age and extremely resistant to change.
P-factor. A tendency for an aircraft to yaw to the left due to
the descending propeller blade on the right producing more
thrust than the ascending blade on the left. This occurs when
the aircraft’s longitudinal axis is in a climbing attitude in
relation to the relative wind. The P-factor would be to the
right if the aircraft had a counterclockwise rotating propeller.
PFD. See primary flight display.
Phugoid oscillations. Long-period oscillations of an
aircraft around its lateral axis. It is a slow change in pitch
accompanied by equally slow changes in airspeed. Angle
of attack remains constant, and the pilot often corrects for
phugoid oscillations without even being aware of them.
PIC. See pilot in command.
Pilotage. Navigation by visual reference to landmarks.