Aeronautical Terms beginning with S
Significant Point
[ICAO Annex 11] A specified geographical location used in defining an ATS route or the flight path of an aircraft and for other navigation and ATS purposes.
Special Instrument Approach Procedure
A procedure approved by the FAA for individual operators, but not published in FAR 97 for public use.
Special Use Airspace Management System (SAMS)
A joint FAA and military program designed to improve civilian access to special use airspace by providing information on whether the airspace is active or scheduled to be active. The information is available to authorized users via an Internet website.
Standard Instrument Departure (SID)
An ATC requested and developed departure route designed to increase capacity of terminal airspace, effectively control the flow of traffic with minimal communication, and reduce environmental impact through noise abatement procedures.
Standard Service Volume
Most air navigation radio aids which provide positive course guidance have a designated standard service volume (SSV). The SSV defines the reception limits of unrestricted NAVAIDS which are usable for random/unpublished route navigation. Standard service volume limitations do not apply to published IFR routes or procedures. See the AIM for the SSV for specific NAVAID types.
Standard Terminal Arrival (STAR)
Provides a common method for departing the en route structure and navigating to your destination. A STAR is a preplanned instrument flight rule ATC arrival procedure published for pilot use in graphic and textual form to simplify clearance delivery procedures. STARs provide you with a transition from the en route structure to an outer fix or an instrument approach fix or arrival waypoint in the terminal area, and they usually terminate with an instrument or visual approach procedure.
Standardized Taxi Routes
Coded taxi routes that follow typical taxiway traffic patterns to move aircraft between gates and runways. ATC issues clearances using these coded routes to reduce radio communication and eliminate taxi instruction misinterpretation.
STAR Transition
A published segment used to connect one or more en route airways, jet routes, or RNAV routes to the basic STAR procedure. It is one of several routes that bring traffic from different directions into one STAR. NACO publishes STARs for airports with procedures authorized by the FAA, and these STARs are included at the front of each Terminal Procedures Publication regional booklet.
Start End of Runway (SER)
The beginning of the takeoff runway available.
Station Declination
The angular difference between true north and the zero radial of a VOR at the time the VOR was last site checked.
Surface Incident
An event during which authorized or unauthorized/unapproved movement occurs in the movement area or an occurrence in the movement area associated with the operation of an aircraft that affects or could affect the safety of flight.
Surface Movement Guidance Control System (SMGCS)
Facilitates the safe movement of aircraft and vehicles at airports where scheduled air carriers are conducting authorized operations. The SMGCS low visibility taxi plan includes the improvement of taxiway and runway signs, markings, and lighting, as well as the creation of SMGCS low visibility taxi route charts.
Synthetic Vision
A visual display of terrain, obstructions, runways, and other surface features that creates a virtual view of what the pilot would see out the window. This tool could be used to supplement normal vision in low visibility conditions, as well as to increase situational awareness in IMC.
Safety (Squat) Switch
An electrical switch mounted on one of the landing gear struts. It is used to sense when the weight of the aircraft is on the wheels.
Scan
A procedure used by the pilot to visually identify all resources of information in flight.
Sea Level
A reference height used to determine standard atmospheric conditions and altitude measurements.
Segmented Circle
A visual ground based structure to provide traffic pattern information.
Service Ceiling
The maximum density altitude where the best rate-of-climb airspeed will produce a 100 feet-per-minute climb at maximum weight while in a clean configuration with maximum continuous power.
Servo Tab
An auxiliary control mounted on a primary control surface, which automatically moves in the direction opposite the primary control to provide an aerodynamic assist in the movement of the control.
Shaft Horse Power (SHP)
Turboshaft engines are rated in shaft horsepower and calculated by use of a dynamometer device. Shaft horsepower is exhaust thrust converted to a rotating shaft.
Shock Waves
A compression wave formed when a body moves through the air at a speed greater than the speed of sound.
Sideslip
A slip in which the airplane’s longitudinal axis remains parallel to the original flightpath, but the airplane no longer flies straight ahead. Instead, the horizontal component of wing lift forces the airplane to move sideways toward the low wing.
Single Engine Absolute Ceiling
The altitude that a twin-engine airplane can no longer climb with one engine inoperative.
Single Engine Service Ceiling
The altitude that a twin-engine airplane can no longer climb at a rate greater then 50 f.p.m. with one engine inoperative.
Skid
A condition where the tail of the airplane follows a path outside the path of the nose during a turn.
Slip
An intentional maneuver to decrease airspeed or increase rate of descent, and to compensate for a crosswind on landing. A slip can also be unintentional when the pilot fails to maintain the aircraft in coordinated flight.
Specific Fuel Consumption
Number of pounds of fuel consumed in 1 hour to produce 1 HP.
Speed
The distance traveled in a given time.
Speed Brakes
A control system that extends from the airplane structure into the airstream to produce drag and slow the airplane.
Speed Instability
A condition in the region of reverse command where a disturbance that causes the airspeed to decrease causes total drag to increase, which in turn, causes the airspeed to decrease further.
Speed Sense
The ability to sense instantly and react to any reasonable variation of airspeed.
Spin
An aggravated stall that results in what is termed an “autorotation” wherein the airplane follows a downward corkscrew path. As the airplane rotates around the vertical axis, the rising wing is less stalled than the descending wing creating a rolling, yawing, and pitching motion.
Spiral Instability
A condition that exists when the static directional stability of the airplane is very strong as compared to the effect of its dihedral in maintaining lateral equilibrium.
Spiraling Slipstream
The slipstream of a propeller-driven airplane rotates around the airplane. This slipstream strikes the left side of the vertical fin, causing the airplane to yaw slightly. Vertical stabilizer offset is sometimes used by aircraft designers to counteract this tendency.
Split Shaft Turbine Engine
See Free Power Turbine Engine.
Spoilers
High-drag devices that can be raised into the air flowing over an airfoil, reducing lift and increasing drag. Spoilers are used for roll control on some aircraft. Deploying spoilers on both wings at the same time allows the aircraft to descend without gaining speed. Spoilers are also used to shorten the ground roll after landing.
Spool
A shaft in a turbine engine which drives one or more compressors with the power derived from one or more turbines.
Stabilator
A single-piece horizontal tail surface on an airplane that pivots around a central hinge point. A stabilator serves the purposes of both the horizontal stabilizer and the elevator.
Stability
The inherent quality of an airplane to correct for conditions that may disturb its equilibrium, and to return or to continue on the original flightpath. It is primarily an airplane design characteristic.
Stabilized Approach
A landing approach in which the pilot establishes and maintains a constant angle glidepath towards a predetermined point on the landing runway. It is based on the pilot’s judgment of certain visual cues, and depends on the maintenance of a constant final descent airspeed and configuration.
Stall
A rapid decrease in lift caused by the separation of airflow from the wing’s surface brought on by exceeding the critical angle of attack. A stall can occur at any pitch attitude or airspeed.
Stall Strips
A spoiler attached to the inboard leading edge of some wings to cause the center section of the wing to stall before the tips. This assures lateral control throughout the stall.
Standard Atmosphere
At sea level, the standard atmosphere consists of a barometric pressure of 29.92 inches of mercury (in. Hg.) or 1013.2 millibars, and a temperature of 15°C (59°F). Pressure and temperature normally decrease as altitude increases. The standard lapse rate in the lower atmosphere for each 1,000 feet of altitude is approximately 1 in. Hg. and 2°C (3.5°F). For example, the standard pressure and temperature at 3,000 feet mean sea level (MSL) is 26.92 in. Hg. 29.92" Hg – 3" Hg) and 9°C (15°C - 6°C).
Standard Day
See Standard Atmosphere.
Standard Empty Weight (GAMA)
This weight consists of the airframe, engines, and all items of operating equipment that have fixed locations and are permanently installed in the airplane; including fixed ballast, hydraulic fluid, unusable fuel, and full engine oil.
Standard Weights
These have been established for numerous items involved in weight and balance computations. These weights should not be used if actual weights are available.
Standard-Rate Turn
A turn at the rate of 3º per second which enables the airplane to complete a 360º turn in 2 minutes.
Starter/Generator
A combined unit used on turbine engines. The device acts as a starter for rotating the engine, and after running, internal circuits are shifted to convert the device into a generator.
Static Stability
The initial tendency an aircraft displays when disturbed from a state of equilibrium.
Station
A location in the airplane that is identified by a number designating its distance in inches from the datum. The datum is, therefore, identified as station zero. An item located at station +50 would have an arm of 50 inches.
Stick Puller
A device that applies aft pressure on the control column when the airplane is approaching the maximum operating speed.
Stick Pusher
A device that applies an abrupt and large forward force on the control column when the airplane is nearing an angle of attack where a stall could occur.
Stick Shaker
An artificial stall warning device that vibrates the control column.
Stress Risers
A scratch, groove, rivet hole, forging defect or other structural discontinuity that causes a concentration of stress.
Subsonic
Speed below the speed of sound.
Supercharger
An engine or exhaust-driven air compressor used to provide additional pressure to the induction air so the engine can produce additional power.
Supersonic
Speed above the speed of sound.
Supplemental Type Certificate (STC)
A certificate authorizing an alteration to an airframe, engine, or component that has been granted an Approved Type Certificate.
Swept Wing
A wing planform in which the tips of the wing are farther back than the wing root.
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.
Selective availability (SA)
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.
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.
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 (360° in 2 minutes) for low- or medium-speed aircraft. For high-speed aircraft, the standard rate turn is 1 1⁄2° per second (360° in 4 minutes).
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.
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.
Scenario-based training (SBT)
Training method that uses a highly structured script of real world experiences to address aviation training objectives in an operational environment.
Selection-type test items
Test items requiring the student to choose from two or more alternatives provided. True-false, matching, and multiple-choice type questions are examples of selection type test items.
Self-concept
A perception factor that ties together how people feel about themselves with how well they receive experiences.
Sensory register
That portion of the brain which receives input from the five senses. The individual’s preconceived concept of what is important determines how the register prioritizes the information for passing it on to the rest of the brain for action.
Single-Pilot Resource Management (SRM)
The art/science of managing all the resources (both onboard the aircraft and from outside sources) available to a single pilot (prior and during flight) to ensure that the successful outcome of the flight is never in doubt.
Sites
Internet addresses which provide information and often are linked to other similar sites.
Situational awareness
The accurate perception and understanding of all the factors and conditions within the four fundamental risk elements that affect safety before, during, and after the flight.
Skill knowledge
Knowledge reflected in motor or manual skills and in cognitive or mental skills that manifests itself in the doing of something.
Skills and procedures
The procedural, psychomotor, and perceptual skills used to control a specific aircraft or its systems. They are the stick and rudder or airmanship abilities that are gained through conventional training, are perfected, and become almost automatic through experience.
Source
In communication, the sender, speaker, transmitter, or instructor who composes and transmits a message made up of symbols which are meaningful to listeners and readers.
Stem
The part of a multiple choice test item consisting of the question, statement, or problem.
Stress management
The personal analysis of the kinds of stress experienced while flying, the application of appropriate stress assessment tools, and other coping mechanisms.
Supply-type test item
Question in which the student supplies answers as opposed to selecting from choices provided. Essay or fill-in-the blank type questions are examples of supply- type test items.
Symbols
In communication, simple oral and visual codes such as words, gestures, and facial expressions which are formed into sentences, paragraphs, lectures, or chapters to compose and transmit a message that means something to the receiver of the information.
Sea level engine
A reciprocating aircraft engine having a rated takeoff power that is producible only at sea level.
Second in command
A pilot who is designated to be second in command of an aircraft during flight time.
Show
Unless the context otherwise requires, to show to the satisfaction of the Administrator.
Small aircraft
Aircraft of 12,500 pounds or less, maximum certificated takeoff weight.
Special VFR conditions
Meteorological conditions that are less than those required for basic VFR flight in controlled airspace and in which some aircraft are permitted flight under visual flight rules.
Special VFR operations
Aircraft operating in accordance with clearances within controlled airspace in meteorological conditions less than the basic VFR weather minima. Such operations must be requested by the pilot and approved by ATC.
Standard atmosphere
The atmosphere defined in U.S. Standard Atmosphere, 1962 (Geopotential altitude tables).
Stopway
An area beyond the takeoff runway, no less wide than the runway and centered upon the extended centerline of the runway, able to support the airplane during an aborted takeoff, without causing structural damage to the airplane, and designated by the airport authorities for use in decelerating the airplane during an aborted takeoff.
Suitable RNAV system
An RNAV system that meets the required performance established for a type of operation, e.g. IFR; and is suitable for operation over the route to be flown in terms of any performance criteria (including accuracy) established by the air navigation service provider for certain routes (e.g. oceanic, ATS routes, and IAPs). An RNAV system’s suitability is dependent upon the availability of ground and/or satellite navigation aids that are needed to meet any route performance criteria that may be prescribed in route specifications to navigate the aircraft along the route to be flown. Information on suitable RNAV systems is published in FAA guidance material.
Synthetic vision
A computer-generated image of the external scene topography from the perspective of the flight deck that is derived from aircraft attitude, high-precision navigation solution, and database of terrain, obstacles and relevant cultural features.
Synthetic vision system
An electronic means to display a synthetic vision image of the external scene topography to the flight crew.
Service Ceiling
The highest altitude at which an aircraft can still maintain a steady rate of climb of 100 feet per minute.
Small Aircraft
An aircraft weighing 12,500 pounds or less, maximum certificated takeoff weight. As defined in 14 CFR part 1.
Standard Empty Weight
(GAMA) Weight of a standard airplane including unusable fuel, full operating fluids, and full oil.
Static Load
The load imposed on an aircraft structure due to the weight of the aircraft and its contents.
Station
(GAMA) A location along the airplane fuselage usually given in terms of distance from the reference datum.
Strain Sensor
A device that converts a physical phenomenon into an electrical signal. Strain sensors in a wheel axle sense the amount the axle deflects and create an electrical signal that is proportional to the force that caused the deflection.
Structural Station
This is a location in the aircraft, such as a bulkhead, which is identified by a number designating its distance in inches or percent MAC from the datum. The datum is, therefore, identified as station zero. The stations and arms are identical. An item located at station +50 would have an arm of 50 inches.
Sublimation
The change of (a) ice to water vapor or (b) water vapor to ice.
Superrefraction
More than normal bending of the radar beam resulting from abnormal vertical gradients of temperature and/or water vapor. (3)
Subrefraction
Less than normal bending of the radar beam resulting from abnormal vertical gradients of temperature and/or water vapor.
St. Elmo’s Fire
A luminous brush discharge of electricity from protruding objects, such as masts and yardarms of ships, aircraft, lightning rods, steeples, etc., occurring in stormy weather. Also called corposant.
Santa Ana
A hot, dry, foehn wind, generally from the northeast or east, occurring west of the Sierra Nevada Mountains especially in the pass and river valley near Santa Ana, California.
Saturated adiabatic lapse rate
The rate of decrease of temperature with height as saturated air is lifted with no gain or loss of heat from outside sources; varies with temperature, being greatest at low temperatures.
Saturation
The condition of the atmosphere when actual water vapor present is the maximum possible at existing temperature.
Scud
Small detached masses of stratus fractus clouds below a layer of higher clouds, usually nimbostratus.
Sea breeze
A coastal breeze blowing from sea to land, caused by the temperature difference when the land surface is warmer than the sea surface. Compare land breeze.
Sea fog
A type of advection fog formed when air that has been lying over a warm surface is transported over a colder water surface.
Sea level pressure
The atmospheric pressure at mean sea level, either directly measured by stations at sea level or empirically determined from the station pressure and temperature by stations not at sea level; used as a common reference for analyses of surface pressure patterns.
Sea smoke
Same as steam fog—fog formed when cold air moves over relatively warm water or wet ground.
Sector visibility
Meteorological visibility within a specified sector of the horizon circle.
Sensitivity time control
A radar circuit designed to correct for range attenuation so that echo intensity on the scope is proportional to reflectivity of the target regardless of range.
Shear
Wind shear. The rate of change of wind velocity (direction and/or speed) per unit distance; conventionally expressed as vertical or horizontal wind shear.
Shower
Precipitation from a cumuliform cloud; characterized by the suddenness of beginning and ending, by the rapid change of intensity, and usually by rapid change in the appearance of the sky; showery precipitation may be in the form of rain, ice pellets, or snow.
Slant visibility
For an airborne observer, the distance at which he can see and distinguish objects on the ground.
Sleet
Ice pellets mixed with rain or snow.
Smog
A mixture of smoke and fog.
Smoke
A restriction to visibility resulting from combustion.
Snow
Precipitation composed of white or translucent ice crystals, chiefly in complex branched hexagonal form.
Snow flurry
Popular term for snow shower, particularly of a very light and brief nature.
Snow grains
Precipitation of very small, white opaque grains of ice, similar in structure to snow crystals. The grains are fairly flat or elongated, with diameters generally less than 0.04 inch (1 mm.).
Snow pellets
Precipitation consisting of white, opaque approximately round (sometimes conical) ice particles having a snow-like structure, and about 0.08 to 0.2 inch in diameter; crisp and easily crushed, differing in this respect from snow grains; rebound from a hard surface and often break up.
Snow shower
Precipitation from a cumuliform cloud; characterized by the suddenness of beginning and ending, by the rapid change of intensity, and usually by rapid change in the appearance of the sky; showery precipitation in the form of ice pellets or snow.
Solar radiation
The total electromagnetic radiation emitted by the sun.
Sounding
In meteorology, an upper-air observation; a radiosonde observation.
Source region
An extensive area of the earth’s surface characterized by relatively uniform surface conditions where large masses of air remain long enough to take on characteristic temperature and moisture properties imparted by that surface.
Specific humidity
The ratio by weight of water vapor in a sample of air to the combined weight of water vapor and dry air. Compare mixing ratio.
Squall
A sudden increase in wind speed by at least 15 knots to a peak of 20 knots or more and lasting for at least one minute. Essential difference between a gust and a squall is the duration of the peak speed.
Squall line
Any nonfrontal line or narrow band of active thunderstorms (with or without squalls).
Stability
A state of the atmosphere in which the vertical distribution of temperature is such that a parcel will resist displacement from its initial level.
Standard atmosphere
A hypothetical atmosphere based on climatological averages comprised of numerous physical constants of which the most important are: (1) A surface temperature of 59° F (15° C) and a surface pressure of 29.92 inches of mercury (1013.2 millibars) at sea level; (2) A lapse rate in the troposphere of 6.5° C per kilometer (approximately 2° C per 1,000 feet); (3) A tropopause of 11 kilometers (approximately 36,000 feet) with a temperature of -56.5° C; and (4) An isothermal lapse rate in the stratosphere to an altitude of 24 kilometers (approximately 80,000 feet).
Standing cloud
A lenticular cloud. (standing lenticular altocumulus) A species of cloud whose elements have the form of more or less isolated, generally smooth lenses or almonds. These clouds appear most often in formations of orographic origin, the result of lee waves, in which case they remain nearly stationary with respect to the terrain (standing cloud), but they also occur in regions without marked orography.
Standing wave
A wave that remains stationary in a moving fluid. In aviation operations it is used most commonly to refer to a lee wave or mountain wave.
Stationary front
Same as quasi-stationary front—a front which is stationary or nearly so; conventionally, a front which is moving at a speed of less than 5 knots is generally considered to be quasi-stationary.
Station pressure
The actual atmospheric pressure at the observing station.
Steam fog
Fog formed when cold air moves over relatively warm water or wet ground.
Storm detection radar
A weather radar designed to detect hydrometeors of precipitation size; used primarily to detect storms with large drops or hailstones as opposed to clouds and light precipitation of small drop size.
Stratiform
Descriptive of clouds of extensive horizontal development, as contrasted to vertically developed cumuliform clouds; characteristic of stable air and, therefore, composed of small water droplets.
Stratocumulus
A low cloud, predominantly stratiform in gray and/or whitish patches or layers, mayor may not merge; elements are tessellated, rounded, or roll-shaped with relatively flat tops.
Stratosphere
The atmospheric layer above the tropopause, average altitude of base and top, 7 and 22 miles respectively; characterized by a slight average increase of temperature from base to top and is very stable; also characterized by low moisture content and absence of clouds.
Stratus
A low, gray cloud layer or sheet with a fairly uniform base; sometimes appears in ragged patches; seldom produces precipitation but may produce drizzle or snow grains. A stratiform cloud.
Stratus fractus
A stratus layer (low, gray cloud layer or sheet) that has a base in the form of irregular shreds (fractus), appearing as if torn.
Streamline
In meteorology, a line whose tangent is the wind direction at any point along the line. A flowline.
Subsidence
A descending motion of air in the atmosphere over a rather broad area; usually associated with divergence.
Summation principle
The principle states that the cover assigned to a layer is equal to the summation of the sky cover of the lowest layer plus the additional coverage at all successively higher layers up to and including the layer in question. Thus, no layer can be assigned a sky cover less than a lower layer, and no sky cover can be greater than 1.0 (10/10).
Superadiabatic lapse rate
A lapse rate greater than the dry-adiabatic lapse rate.
Supercooled water
Liquid water at temperatures colder than freezing.
Surface inversion
An inversion with its base at the surface, often caused by cooling of the air near the surface as a result of terrestrial radiation, especially at night.
Surface visibility
Visibility observed from eye-level above the ground.
Synoptic chart
A chart, such as the familiar weather map, which depicts the distribution of meteorological conditions over an area at a given time.
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.
Sea breeze
A coastal breeze blowing from sea to land caused by the temperature difference when the land surface is warmer than the sea surface. The sea breeze usually occurs during the day and alternates with the land breeze that blows in the opposite direction at night.
Sea level engine
A reciprocating aircraft engine having a rated takeoff power that is producible only at sea level.
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.
Sectional aeronautical charts
Designed for visual navigation of slow- or medium-speed aircraft. Topographic information on these charts features the portrayal of relief, and a judicious selection of visual check points for VFR flight. Aeronautical information includes visual and radio aids to navigation, airports, controlled airspace, restricted areas, obstructions and related data.
Selective availability (SA)
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.
Semimonocoque
A fuselage design that includes a substructure of bulkheads and/or formers, along with stringers, to support flight loads and stresses imposed on the fuselage.
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.
Service ceiling
The maximum density altitude where the best rate-of-climb airspeed will produce a 100-feet-per-minute climb at maximum weight while in a clean configuration with maximum continuous power.
Servo
A motor or other form of actuator which receives a small signal from the control device and exerts a large force to accomplish the desired work.
Servo tab
An auxiliary control mounted on a primary control surface, which automatically moves in the direction opposite the primary control to provide an aerodynamic assist in the movement of the control.
Signal-to-noise ratio
An indication of signal strength received compared to background noise, which is a measure of the adequacy of the received signal.
Significant weather prognostic
Presents four panels showing forecast significant weather.
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 a 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.
Skills and procedures
The procedural, psychomotor, and perceptual skills used to control a specific aircraft or its systems. They are the airmanship abilities that are gained through conventional training, are perfected, and become almost automatic through experience.
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 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 flight permit
A flight permit issued to an aircraft that does not meet airworthiness requirements but is capable of safe flight. A special flight permit can be issued to move an aircraft for the purposes of maintenance or repair, buyer delivery, manufacturer flight tests, evacuation from danger, or customer demonstration. Also referred to as a ferry permit.
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.
Special fuel consumption
The amount of fuel in pounds per hour consumed or required by an engine per brake horsepower or per pound of thrust.
Speed
The distance traveled in a given time.
Spin
An aggravated stall that results in an airplane descending in a helical, or corkscrew path.
Spiral instability
A condition that exists when the static directional stability of the airplane is very strong as compared to the effect of its dihedral in maintaining lateral equilibrium.
Spiraling slipstream
The slipstream of a propeller-driven airplane rotates around the airplane. This slipstream strikes the left side of the vertical fin, causing the aircraft to yaw slightly. Rudder offset is sometimes used by aircraft designers to counteract this tendency.
Spoilers
High-drag devices that can be raised into the air flowing over an airfoil, reducing lift and increasing drag. Spoilers are used for roll control on some aircraft. Deploying spoilers on both wings at the same time allows the aircraft to descend without gaining speed. Spoilers are also used to shorten the ground roll after landing.
Stabilator
A single-piece horizontal tail surface on an airplane that pivots around a central hinge point. A stabilator serves the purposes of both the horizontal stabilizer and the elevators.
Stability
The inherent quality of an airplane to correct for conditions that may disturb its equilibrium, and to return or to continue on the original flightpath. It is primarily an airplane design characteristic.
Stagnant hypoxia
A type of hypoxia that results when the oxygen-rich blood in the lungs is not moving to the tissues that need it.
Stall
A rapid decrease in lift caused by the separation of airflow from the wing’s surface, brought on by exceeding the critical angle of attack. A stall can occur at any pitch attitude or airspeed.
Standard atmosphere
At sea level, the standard atmosphere consists of a barometric pressure of 29.92 inches of mercury ("Hg) or 1013.2 millibars, and a temperature of 15°C (59°F). Pressure and temperature normally decrease as altitude increases. The standard lapse rate in the lower atmosphere for each 1,000 feet of altitude is approximately 1"Hg and 2°C (3.5°F). For example, the standard pressure and temperature at 3,000 feet mean sea level (MSL) are 26.92"Hg (29.92"Hg – 3"Hg) and 9°C (15°C – 6°C).
Standard empty weight (GAMA)
This weight consists of the airframe, engines, and all items of operating equipment that have fixed locations and are permanently installed in the airplane including fixed ballast, hydraulic fluid, unusable fuel, and full engine oil.
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 (360° in 2 minutes) for low- or medium-speed aircraft. For high-speed aircraft, the standard rate turn is 1 1⁄2° per second (360° in 4 minutes).
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.
Standard weights
Weights established for numerous items involved in weight and balance computations. These weights should not be used if actual weights are available.
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.
Static stability
The initial tendency an aircraft displays when disturbed from a state of equilibrium.
Station
A location in the airplane that is identified by a number designating its distance in inches from the datum. The datum is, therefore, identified as station zero. An item located at station +50 would have an arm of 50 inches.
Stationary front
A front that is moving at a speed of less than 5 knots.
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.
Stratoshere
A layer of the atmosphere above the tropopause extending to a height of approximately 160,000 feet.
Stress
The body’s response to demands placed upon it.
Stress management
The personal analysis of the kinds of stress experienced while flying, the application of appropriate stress assessment tools, and other coping mechanisms.
Structural icing
The accumulation of ice on the exterior of the aircraft.
Sublimation
Process by which a solid is changed to a gas without going through the liquid state.
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.
Supercharger
An engine- or exhaust-driven air compressor used to provide additional pressure to the induction air so the engine can produce additional power.
Supercooled water droplets
Water droplets that have been cooled below the freezing point, but are still in a liquid state.
Surface analysis chart
A report that depicts an analysis of the current surface weather. Shows the areas of high and low pressure, fronts, temperatures, dewpoints, wind directions and speeds, local weather, and visual obstructions.
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.
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