Profile view. Side view of an IAP chart illustrating the vertical
approach path altitudes, headings, distances, and fixes.
Prohibited area. Designated airspace within which flight of
aircraft is prohibited.
Propeller/rotor modulation error. Certain propeller RPM
settings or helicopter rotor speeds can cause the VOR course
deviation indicator (CDI) to fluctuate as much as ±6°. Slight
changes to the RPM setting will normally smooth out this
roughness.
Rabbit, the. High-intensity flasher system installed at many
large airports. The flashers consist of a series of brilliant
blue-white bursts of light flashing in sequence along the
approach lights, giving the effect of a ball of light traveling
towards the runway.
Radar. Radio Detection And Ranging.
Radar approach. The controller provides vectors while
monitoring the progress of the flight with radar, guiding
the pilot through the descent to the airport/heliport or to a
specific runway.
Radials. The courses oriented from a station.
Radio or radar altimeter. An electronic altimeter that
determines the height of an aircraft above the terrain by
measuring the time needed for a pulse of radio-frequency
energy to travel from the aircraft to the ground and return.
Radio frequency (RF). A term that refers to alternating
current (AC) having characteristics such that, if the current is
input to antenna, an electromagnetic (EM) field is generated
suitable for wireless broadcasting and/or communications.
Radio magnetic indicator (RMI). An electronic navigation
instrument that combines a magnetic compass card with two
bearing pointers (typically). Generally, one pointer is for the
ADF while the other is for an RNAV or VOR navigation
system. The pointers are typically different colors and of
different widths for ease of identification. Sometimes a
function switch is provided to allow the #2 pointer to be
slaved to either a VOR or RNAV system. The card of the
RMI acts as a gyro-stabilized magnetic compass (usually
corrected for north via a flux valve) and shows the magnetic
heading the aircraft is flying.
Radio wave. An electromagnetic wave (EM wave) with
frequency characteristics useful for radio transmission.
RAIM. See receiver autonomous integrity monitoring.
Random RNAV routes. Direct routes, based on area
navigation capability, between waypoints defined in terms
of latitude/longitude coordinates, degree-distance fixes, or
offsets from established routes/airways at a specified distance
and direction.
Ranging signals. Transmitted from the GPS satellite, these
allow the aircraft’s receiver to determine range (distance)
from each satellite.
RB. See relative bearing.
RBI. See relative bearing indicator.
RCO. See remote communications outlet.
Receiver autonomous integrity monitoring (RAIM).
A system used to verify the usability of the received GPS
signals and warns the pilot of any malfunction in the
navigation system. This system is required for IFR-certified
GPS units.
Recommended altitude. An altitude depicted on an
instrument approach chart with the altitude value neither
underscored nor overscored. The depicted value is an
advisory value.
Receiver-transmitter (RT). A system that permits selection
of a unique channel or frequency whereupon a signal (typically
communication) can be transmitted and received.
Reduced vertical separation minimum (RVSM). Reduces
the vertical separation between flight level (FL) 290–410
from 2,000 feet to 1,000 feet and makes six additional FLs
available for operation. Also see DRVSM.
Reference circle (also, distance circle). The circle depicted
in the plan view of an IAP chart that typically has a 10 NM
radius, within which chart the elements are drawn to scale.
Regions of command. The “regions of normal and reversed
command” refers to the relationship between speed and the
power required to maintain or change that speed in flight.
REIL. See runway end identifier lights.
Relative bearing (RB). The angular difference between the
aircraft heading and the direction to the station, measured
clockwise from the nose of the aircraft.
Relative bearing indicator (RBI). Also known as the fixed-
card ADF, zero is always indicated at the top of the instrument
and the needle indicates the relative bearing to the station.
Relative wind. Direction of the airflow produced by an object
moving through the air. The relative wind for an airplane in
flight flows in a direction parallel with and opposite to the
direction of flight; therefore, the actual flight path of the
airplane determines the direction of the relative wind.
Remote communications outlet (RCO). An unmanned
communications facility that is remotely controlled by air
traffic personnel.
Required navigation performance (RNP). A specified level
of accuracy defined by a lateral area of confined airspace in
which an RNP-certified aircraft operates.
Restricted area. Airspace designated under 14 CFR part
73 within which the flight of aircraft, while not wholly
prohibited, is subject to restriction.
Reverse sensing. The VOR needle appearing to indicate the
reverse of normal operation.
RF. Radio frequency.
Rhodopsin. The photosensitive pigments that initiate the
visual response in the rods of the eye.
Rigidity. The characteristic of a gyroscope that prevents its
axis of rotation tilting as the Earth rotates.
Rime ice. Rough, milky, opaque ice formed by the
instantaneous freezing of small supercooled water droplets.
Risk. The future impact of a hazard that is not eliminated
or controlled.
RMI. See radio magnetic indicator.
RNAV. See area navigation.
RNP. See required navigation performance.
Runway end identifier lights (REIL). A pair of synchronized
flashing lights, located laterally on each side of the runway
threshold, providing rapid and positive identification of the
approach end of a runway.
Runway visibility value (RVV). The visibility determined
for a particular runway by a transmissometer.
Runway visual range (RVR). The instrumentally derived
horizontal distance a pilot should be able to see down the
runway from the approach end, based on either the sighting
of high-intensity runway lights, or the visual contrast of
other objects.
RVR. See runway visual range.
RVV. See runway visibility value.
St. Elmo’s Fire. A corona discharge which lights up the aircraft
surface areas where maximum static discharge occurs.
Satellite ephemeris data. Data broadcast by the GPS
satellite containing very accurate orbital data for that
satellite, atmospheric propagation data, and satellite clock
error data.
Scan. The first fundamental skill of instrument flight, also
known as “cross-check;” the continuous and logical observation
of instruments for attitude and performance information.
SDF. See simplified directional facility.
Selective availability. A satellite technology permitting the
Department of Defense (DOD) to create, in the interest of
national security, a significant clock and ephemeris error in
the satellites, resulting in a navigation error.
Semicircular canal. An inner ear organ that detects angular
acceleration of the body.
Sensitive altimeter. A form of multipointer pneumatic
altimeter with an adjustable barometric scale that allows the
reference pressure to be set to any desired level.
SIDS. See standard instrument departure procedures.
SIGMET. The acronym for Significant Meteorological
information. A weather advisory issued concerning weather
significant to the safety of all aircraft.
Signal-to-noise ratio. An indication of signal strength
received compared to background noise, which is a measure
of how adequate the received signal is.
Simplex. Transmission and reception on the same
frequency.
Simplified directional facility (SDF). A NAVAID used
for nonprecision instrument approaches. The final approach
course is similar to that of an ILS localizer; however, the
SDF course may be offset from the runway, generally not
more than 3°, and the course may be wider than the localizer,
resulting in a lower degree of accuracy.
Single-pilot resource management (SRM). The ability for
crew or pilot to manage all resources effectively to ensure
the outcome of the flight is successful.
Situational awareness. Pilot knowledge of where the
aircraft is in regard to location, air traffic control, weather,
regulations, aircraft status, and other factors that may affect
flight.
Skidding turn. An uncoordinated turn in which the rate of
turn is too great for the angle of bank, pulling the aircraft to
the outside of the turn.
Skin friction drag. Drag generated between air molecules
and the solid surface of the aircraft.
Slant range. The horizontal distance from the aircraft antenna
to the ground station, due to line-of-sight transmission of the
DME signal.
Slaved compass. A system whereby the heading gyro is
“slaved to,” or continuously corrected to bring its direction
readings into agreement with a remotely located magnetic
direction sensing device (usually this is a flux valve or flux
gate compass).
Slipping turn. An uncoordinated turn in which the aircraft
is banked too much for the rate of turn, so the horizontal lift
component is greater than the centrifugal force, pulling the
aircraft toward the inside of the turn.
Small airplane. An airplane of 12,500 pounds or less
maximum certificated takeoff weight.
Somatogravic illusion. The misperception of being
in a nose-up or nose-down attitude, caused by a rapid
acceleration or deceleration while in flight situations that
lack visual reference.
Spatial disorientation. The state of confusion due to
misleading information being sent to the brain from various
sensory organs, resulting in a lack of awareness of the aircraft
position in relation to a specific reference point.
Special use airspace. Airspace in which flight activities are
subject to restrictions that can create limitations on the mixed
use of airspace. Consists of prohibited, restricted, warning,
military operations, and alert areas.
SRM. See single-pilot resource management.
SSR. See secondary surveillance radar.
SSV. See standard service volume.
Standard holding pattern. A holding pattern in which all
turns are made to the right.
Standard instrument departure procedures (SIDS).
Published procedures to expedite clearance delivery and to
facilitate transition between takeoff and en route operations.
Standard rate turn. A turn in which an aircraft changes its
direction at a rate of 3° per second. The turn indicators are
typically 2 minute or 4 minute instruments. In a 2 minute
instrument, if the needle is one needle width either side of
the center alignment mark, the turn is 3° per second and the
turn takes 2 minutes to execute a 360° turn. In a 4 minute
instrument, the same turn takes two widths deflection of the
needle to achieve 3° per second. The 4 minute turn instrument
is usually found on high performance aircraft.
Standard service volume (SSV). Defines the limits of the
volume of airspace which the VOR serves.
Standard terminal arrival route (STAR). A preplanned
IFR ATC arrival procedure published for pilot use in graphic
and/or textual form.
STAR. See standard terminal arrival route.
Static longitudinal stability. The aerodynamic pitching
moments required to return the aircraft to the equilibrium
angle of attack.
Static pressure. Pressure of air that is still, or not moving,
measured perpendicular to the surface of the aircraft.
Steep turns. In instrument flight, any turn greater than standard
rate; in visual flight, anything greater than a 45° bank.
Stepdown fix. The point after which additional descent is
permitted within a segment of an IAP.
Strapdown system. An INS in which the accelerometers
and gyros are permanently “strapped down” or aligned with
the three axes of the aircraft.
Stress. The body’s response to demands placed upon it.
Structural icing. The accumulation of ice on the exterior
of the aircraft.
Suction relief valve. A relief valve in an instrument vacuum
system required to maintain the correct low pressure inside
the instrument case for the proper operation of the gyros.
Synchro. A device used to transmit indications of angular
movement or position from one location to another.
Synthetic vision. A realistic display depiction of the aircraft
in relation to terrain and flight path.
TAA. See terminal arrival area.
TACAN. See tactical air navigation.
Tactical air navigation (TACAN). An electronic navigation
system used by military aircraft, providing both distance and
direction information.
TAWS. See terrain awareness and warning system.
TCAS. See traffic alert collision avoidance system.
TCH. See threshold crossing height.
TDZE. See touchdown zone elevation.
TEC. See Tower En Route Control.
Technique. The manner in which procedures are executed.
Temporary flight restriction (TFR). Restriction to flight
imposed in order to:
1. Protect persons and property in the air or on the
surface from an existing or imminent flight associated
hazard;
2. Provide a safe environment for the operation of
disaster relief aircraft;
3. Prevent an unsafe congestion of sightseeing aircraft
above an incident;
4. Protect the President, Vice President, or other public
figures; and,
5. Provide a safe environment for space agency
operations.
Pilots are expected to check appropriate NOTAMs during
flight planning when conducting flight in an area where a
temporary flight restriction is in effect.
Tension. Maintaining an excessively strong grip on the control
column, usually resulting in an overcontrolled situation.
Terminal Instrument Approach Procedure (TERP).
Prescribes standardized methods for use in designing
instrument flight procedures.
Terminal arrival area (TAA). A procedure to provide a
new transition method for arriving aircraft equipped with
FMS and/or GPS navigational equipment. The TAA contains
a “T” structure that normally provides a NoPT for aircraft
using the approach.
TERP. See terminal instrument approach procedure.
Terrain Awareness and Warning System (TAWS). A
timed-based system that provides information concerning
potential hazards with fixed objects by using GPS positioning
and a database of terrain and obstructions to provide true
predictability of the upcoming terrain and obstacles.
TFR. See temporary flight restriction.
Threshold crossing height (TCH). The theoretical height
above the runway threshold at which the aircraft’s glide
slope antenna would be if the aircraft maintains the trajectory
established by the mean ILS glide slope or MLS glide path.
Thrust (aerodynamic force). The forward aerodynamic
force produced by a propeller, fan, or turbojet engine as it
forces a mass of air to the rear, behind the aircraft.
Time and speed table. A table depicted on an instrument
approach procedure chart that identifies the distance from the
FAF to the MAP, and provides the time required to transit
that distance based on various groundspeeds.
Timed turn. A turn in which the clock and the turn
coordinator are used to change heading a definite number of
degrees in a given time.
TIS. See traffic information service.
Title 14 of the Code of Federal Regulations (14 CFR).
The federal aviation regulations governing the operation of
aircraft, airways, and airmen.
Touchdown zone elevation (TDZE). The highest elevation
in the first 3,000 feet of the landing surface, TDZE is
indicated on the instrument approach procedure chart when
straight-in landing minimums are authorized.
Tower En Route Control (TEC). The control of IFR en route
traffic within delegated airspace between two or more adjacent
approach control facilities, designed to expedite traffic and
reduce control and pilot communication requirements.
TPP. See United States Terminal Procedures Publication.
Tracking. Flying a heading that will maintain the desired track
to or from the station regardless of crosswind conditions.
Traffic Alert Collision Avoidance System (TCAS).
An airborne system developed by the FAA that operates
independently from the ground-based Air Traffic Control
system. Designed to increase flight deck awareness of
proximate aircraft and to serve as a “last line of defense” for
the prevention of mid-air collisions.
Traffic information service (TIS). A ground-based service
providing information to the flight deck via data link using
the S-mode transponder and altitude encoder to improve the
safety and efficiency of “see and avoid” flight through an
automatic display that informs the pilot of nearby traffic.
Transcribed Weather Broadcast (TWEB). Meteorological
and aeronautical data recorded on tapes and broadcast over
selected NAVAIDs. Generally, the broadcast contains route-
oriented data with specially prepared NWS forecasts, inflight
advisories, and winds aloft. It also includes selected current
information such as weather reports (METAR/SPECI),
NOTAMs, and special notices.
Transponder. The airborne portion of the ATC radar
beacon system.
Transponder code. One of 4,096 four-digit discrete codes
ATC assigns to distinguish between aircraft.
Trend. Immediate indication of the direction of aircraft
movement, as shown on instruments.
Trim. Adjusting the aerodynamic forces on the control
surfaces so that the aircraft maintains the set attitude without
any control input.
TWEB. See Transcribed Weather Broadcast.
True airspeed. Actual airspeed, determined by applying a
correction for pressure altitude and temperature to the CAS.
UHF. See ultra-high frequency.
Ultra-high frequency (UHF). The range of electromagnetic
frequencies between 962 MHz and 1213 MHz.
Uncaging. Unlocking the gimbals of a gyroscopic instrument,
making it susceptible to damage by abrupt flight maneuvers
or rough handling.
Underpower. Using less power than required for the purpose
of achieving a faster rate of airspeed change.
United States Terminal Procedures Publication (TPP).
Booklets published in regional format by the NACO that
include DPs, STARs, IAPs, and other information pertinent
to IFR flight.
Unusual attitude. An unintentional, unanticipated, or
extreme aircraft attitude.
User-defined waypoints. Waypoint location and other data
which may be input by the user, this is the only GPS database
information that may be altered (edited) by the user.
Variation. Compass error caused by the difference in
the physical locations of the magnetic north pole and the
geographic north pole.
VASI. See visual approach slope indicator.
VDP. See visual descent point.
Vectoring. Navigational guidance by assigning headings.
Venturi tube. A specially shaped tube attached to the outside
of an aircraft to produce suction to allow proper operation
of gyro instruments.
Vertical speed indicator (VSI). A rate-of-pressure change
instrument that gives an indication of any deviation from a
constant pressure level.
Very-high frequency (VHF). A band of radio frequencies
falling between 30 and 300 MHz.
Very-high frequency omnidirectional range (VOR).
Electronic navigation equipment in which the flight deck
instrument identifies the radial or line from the VOR station,
measured in degrees clockwise from magnetic north, along
which the aircraft is located.
Vestibule. The central cavity of the bony labyrinth of the ear,
or the parts of the membranous labyrinth that it contains.
VFR. See visual flight rules.
VFR-on-top. ATC authorization for an IFR aircraft to operate
in VFR conditions at any appropriate VFR altitude.
VFR over-the-top. A VFR operation in which an aircraft
operates in VFR conditions on top of an undercast.
Victor airways. Airways based on a centerline that extends
from one VOR or VORTAC navigation aid or intersection,
to another navigation aid (or through several navigation aids
or intersections); used to establish a known route for en route
procedures between terminal areas.
Visual approach slope indicator (VASI). A visual aid of
lights arranged to provide descent guidance information
during the approach to the runway. A pilot on the correct
glide slope will see red lights over white lights.
Visual descent point (VDP). A defined point on the final
approach course of a nonprecision straight-in approach
procedure from which normal descent from the MDA to the
runway touchdown point may be commenced, provided the
runway environment is clearly visible to the pilot.
Visual flight rules (VFR). Flight rules adopted by the
FAA governing aircraft flight using visual references. VFR
operations specify the amount of ceiling and the visibility the
pilot must have in order to operate according to these rules.
When the weather conditions are such that the pilot can not
operate according to VFR, he or she must use instrument
flight rules (IFR).
Visual meteorological conditions (VMC). Meteorological
conditions expressed in terms of visibility, distance from
cloud, and ceiling meeting or exceeding the minimums
specified for VFR.
VMC. See visual meteorological conditions.
VOR. See very-high frequency omnidirectional range.
VORTAC. A facility consisting of two components, VOR
and TACAN, which provides three individual services: VOR
azimuth, TACAN azimuth, and TACAN distance (DME) at
one site.
VOR test facility (VOT). A ground facility which emits a
test signal to check VOR receiver accuracy. Some VOTs are
available to the user while airborne, while others are limited
to ground use only.
VOT. See VOR test facility.
VSI. See vertical speed indicator.
WAAS. See wide area augmentation system.
Warning area. An area containing hazards to any aircraft
not participating in the activities being conducted in the
area. Warning areas may contain intensive military training,
gunnery exercises, or special weapons testing.
Waypoint. A designated geographical location used for route
definition or progress-reporting purposes and is defined in
terms of latitude/longitude coordinates.
WCA. See wind correction angle.
Weather and radar processor (WARP). A device that
provides real-time, accurate, predictive and strategic weather
information presented in an integrated manner in the National
Airspace System (NAS).
Weight. The force exerted by an aircraft from the pull of
gravity.
Wide area augmentation system (WAAS). 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.
Wind correction angle (WCA). The angle between the
desired track and the heading of the aircraft necessary to
keep the aircraft tracking over the desired track.
Wind shear. A change in wind speed and/or wind direction
in a short distance.
Work. A measurement of force used to produce movement.
Zone of confusion. Volume of space above the station where
a lack of adequate navigation signal directly above the VOR
station causes the needle to deviate.