Glossary - Letter S

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S |abbreviation| south

Saab 340 |noun| a small Swedish twin turboprop regional transport aircraft, still in operation, but no longer in production

safe |adjective| free from danger / Approach to land must be made at a safe speed. / - safe landing > a landing which does not endanger people or damage the aircraft.


safeguard |noun| something done as a precaution / A propeller is feathered after engine failure, or as a safeguard when low oil pressure or excessive temperature have indicated the development of a possible defect. / - |verb| to take action to make sure that something is protected from harm / A pressure maintaining valve is generally used to safeguard operation of important services, such as flying controls and wheel brakes. /


safe life |noun| the principle of putting the least load or force on each component, so that it will last well beyond a plane’s expected life


safety |noun| freedom from danger, injury or risk / Turbulence can have serious effects on aircraft safety and performance and makes air travel uncomfortable. / - safety conscious > the state of being aware at all times of the importance of safety and the means by which it is achieved and maintained


safety pilot |noun| a pilot present in the cockpit to ensure the safety of the flight, e.g. when a student is practicing instrument flying


safety regulations |plural noun| rules or laws which must be followed to make a place safe / Equipment and furnishings on modern jet transports must comply with safety regulations concerning fire resistance. /


safety straps |plural noun| device to keep a person in position in a seat


sailplane |noun| a light glider particularly well adapted to making use of rising air currents


St Elmo’s Fire |noun| a luminous electrical discharge sometimes seen on aircraft during storms


SALR |abbreviation| saturated adiabatic lapse rate


salvage |verb| to save items of property which may be in danger of being lost / In the event of a crash landing in a remote area on land, an attempt should be made to salvage all items of survival equipment from the wreckage including beacons, rafts and raft equipment. /


sample |noun| a small amount which is representative of the whole / If a sample of fuel taken from a tank was found to be hazy or cloudy in appearance, this would indicate the presence of water in suspension. If fuel contamination by water is suspected, a sample of fuel should be drained from the tank for inspection. /


sandwich |noun| a construction of three layers, the material of the one in the middle being different from the two on each side / Standard connectors consist of a metal coupling with a rubber sandwich joint. /


SAR |abbreviation|  1. special aerodrome report  2. search and rescue (ICAO)


SAS |abbreviation| stability augmentation system


satellite |noun|  1. an object launched to orbit the earth, usually receiving and transmitting signals, pictures and data / Satellite communications improve the effective distribution of world area forecasts.2. a terminal building at an airport, attached to a larger terminal, which is located to bring passengers nearer to the gates


satellite navigation, satellite navigation system |noun| a system of navigation which uses orbiting satellites to determine the position of an aircraft or point, in relation to the Earth’s surface. Abbreviation: SATNAV


satisfactory |adjective| adequate, good enough / For satisfactory operation, an engine requires an adequate supply of oil. / ‘…during the engine run-up, check that the use of carburetor heat gives a satisfactory drop in rpm or manifold pressure’ [Civil Aviation Authority, General Aviation Safety Sense Leaflet]


satisfy |verb|  1. to meet a particular prescribed standard / Shell Avgas 100LL satisfies British specification. /  2. to meet the needs or requirements of something / To satisfy the requirements of aviation there are three types of meteorological offices for aviation, each with a specific role to fulfill. /


SATNAV |abbreviation| satellite navigation


saturate |verb| to cause a substance to combine with the greatest possible amount of another substance / When a sample of air contains the maximum amount of water vapor for its particular temperature, it is said to be saturated. /


saturation |noun| the state of being filled with the maximum amount of something which can be absorbed, e.g. a sample of air which contains the maximum amount of water vapor for its temperature / The various types of fog are classified by the manner in which saturation is reached. / - the moisture in the air reached saturation point and fell as rain > the air could absorb no more water


saturation point |noun| the level at which no more of a substance can be absorbed


save |verb| to prevent unnecessary use of / Electromagnetic switches are generally used to control high-current devices by means of a small current thus saving heavy duty cable and therefore weight. /


SB |abbreviation| service bulletin


scale |noun|  1. marks at fixed intervals used as a reference standard in measurement / This ruler has scales in inches and centimeters. /  2. a graded system of classification  3. a proportion used in determining distance on charts / Many aeronautical charts use a scale of 1:500,000. /


scan |verb|  1. to look at quickly and systematically / The pilot is trained to scan the instrument panel. /  2. to move a radar beam in a systematic pattern in search of a target / Some radars scan in azimuth and glide-slope. /


scatter |noun| deflection of radiation / High frequencies are freer of ionospheric scatter and are relatively free of noise. /

scattered |adjective| showers or clouds which are distributed irregularly / PAEL 182245Z 30010KT 25SM SCT050 / Abbreviation: SCT

schedule |noun|  1. a list of times of departures and arrivals  2. a printed or written list of items in the form of a table / inspection schedule, maintenance schedule / - |verb|  1. to plan for a particular time or date / The meeting is scheduled for 3 o’clock. /  2. to enter on a schedule / Calculate and schedule each item on the proper form. /


scheduled |adjective| - scheduled landing > an arrival at a timetabled destination


scheduled flights |plural noun| flights that are listed in the airline timetable, as opposed to charter flights


schematic |adjective| showing the function of a device or system without trying to create a realistic image / Figure 3 shows a schematic diagram of the autopilot. /

scissor lift loader |noun| a telescopic loader for raising containers and pallets to the cargo compartments

scram-jet |noun| a ramjet aircraft in which fuel is burned in air that is moving at supersonic speeds


screen |noun| the surface of a TV or computer monitor on which the image is seen / The airborne weather radar (AWR) allows the range of cloud to be estimated from range markers displayed on the screen. /


screw |noun| a type of threaded connector used to fix things together by rotating it


screw jack, screw-jack |noun| a lifting device working with rotary input / Pitch trim is achieved by lowering or raising the tailplane leading edge with a screw jack powered by two hydraulic motors. /


sea |noun|  1. a body of salt water between land masses / Swissair flight 111 crashed into the sea. / - mean sea level > the average level of the sea taking tidal variations into account / Altitude is the vertical distance between an aircraft – or a point or a level – and mean sea level. /  2. a particular area of a body of salt water / the North Sea, the South China Sea, ocean /


sea-anchor |noun| a device under a raft to provide stability /Each life raft is equipped with a flame orange colored canopy and a sea-anchor./


seaboard |noun| US a coast / the eastern seaboard of the USA /


seal |noun|  1. a device that joins two parts and prevents leakage / An oil seal reduces the clearance between the rotating and static members. / - static seal > a seal which is part of a non-moving component / Static seals, gaskets and packing are used in many locations. /  2. a way in which a liquid or a gas may be prevented from escaping / Static seals, gaskets and packing effect a seal by being squeezed between two surfaces. / - |verb| to join two parts in such a way as to prevent leakage / In pressurized aircraft, bulkheads are provided at the front and rear ends of the fuselage to seal off the crew compartment and the passenger cabin. /


sealant |noun| a substance painted or sprayed onto a surface to prevent the escape of a liquid or gas / The integral fuel tank may be completely coated on the inside with a layer of sealant. /


sea level |noun| the average level of the surface of the sea, used for measuring barometric pressure


sealing compound |noun| same as sealant


seaplane |noun| a plane that can take off from and land on water


search |noun| an act of looking for something in order to find it / The aircraft reduced altitude and carried out a visual search for survivors. / - |verb| to look for in order to find something / The investigators searched the scene of the crash for the flight data recorder. /


season |noun| one of the four natural divisions of the year, spring, summer, autumn, or winter / The amount of solar radiation received by the Earth depends on the season. /


seasonal |adjective|  1. referring to the four natural divisions of the year, or characteristic of a particular time of the year / seasonal temperatures, seasonal winds /  2. only lasting for a season / seasonal work /


seasonal variation |noun| a change occurring according to the season


seat |noun| a place for sitting / pilot’s seat / - window seat > a seat next to a window


seated |adjective| sitting, on your seat / Passengers should remain seated. /


seating capacity |noun| the maximum number of people that can seat in an aircraft, bus, etc.


secondary |adjective|  1. of the second rank in importance, etc., not primary  2. an induced current that is generated by a primary source


secondary radar |noun| a radar system in which the active target replies to the interrogation unit


secondary surveillance radar |noun| a radar which uses ground equipment called interrogators and airborne equipment called transponders to identify aircraft, determine altitude and range, etc. / Secondary surveillance radar (SSR) is normally used to supplement data from primary systems. / Abbreviation: SSR


section |noun|  1. a component or part of a structure / tail section and nose section of the aircraft, the non-smoking section of the aircraft /  2. part of a text / The book is divided into four sections, and the first four chapters form the first section. /  3. a diagram of a solid object as it would appear if cut, so that the internal structure is displayed / cross-section /


sectional |adjective|  1. referring to a section or composed of sections  2. showing a solid object as it would appear if it were cut


sector |noun|  1. part of the flight between an aircraft moving under its own power until it next stops after landing in its allocated parking position / On some sectors, because of fuel costs at the destination, it can be economical to carry excess fuel. /  2. the portion of a circle inside two radii and the included arc  3. a segment of airspace with its own team of air traffic controllers


secure |adjective| fastened or locked, safe / Overhead baggage lockers must be secure. / - |verb| to attach firmly, to fasten or to make safe / If the onset of turbulence is sudden, crew must immediately secure themselves in the nearest available seats. /

security |noun|  1. safety  2. people whose job is to protect buildings or other people against crime

seize |verb|  1. to block, lock or jam / The flap linkage appears to be seized up. /  2. to grab or take hold of / Seize the handle and turn clockwise. /

SELCAL |noun| a high-frequency radio system which alerts the crew of an aircraft to the fact that air traffic control is trying to contact them. Full form: selective call


seldom |adverb| not often, rarely /Aircraft are seldom hit by lightning. The wet sump system of lubrication is seldom used on modern aircraft./


select |verb| to choose something such as a particular instrument or system setting / A reverse thrust lever in the crew compartment is used to select reverse thrust. The cabin pressure controller is used to select cabin altitude. /


selection |noun|  1. a choice of something such as a particular instrument or system setting / By manual selection of the heating switch, the formed ice can be dispersed. /  2. a collection of carefully chosen things / a selection of photographs /


selector |noun| a manually operated device like a switch, which offers a choice of settings / Turn the selector control. The purpose of this selector is to direct fluid to the appropriate side of an actuator. /


self-contained |adjective| independent / The auxiliary power unit is a self-contained unit. /


self-positioning |noun| the positioning of the aircraft on the extended center-line of the runway using the on-board navigation system. Also called: center fix


semi- |prefix| half


semicircle |noun| half a circle / Most mathematical protractors are made of plastic in the shape of a semicircle. /


semicircular |adjective| in the shape of half a circle / Most mathematical protractors are semicircular in shape. /


semiconductor |noun| a solid crystalline substance with electrical conductivity greater than insulators but less than good conductors / Semiconductor material is used to make many electronic devices. /


senior |adjective| older or more important in rank / senior cabin supervisor /


sense |noun|  1. manner, way / After turning the aircraft, the auto-control will operate in the opposite sense and return the ailerons to neutral as the aircraft returns to level flight. /  2. any of the physiological means by which we experience our surroundings: sight, hearing, smell, taste and touch / When flying in cloud, pilots must rely on the instruments and not on their senses. /  3. wisdom or natural intelligence / He has a lot of (common) sense. /  4. the meaning of a word / The word ‘bearing’ is used in a lot of different senses. / - |verb| to detect automatically / The fire warning system is designed to sense two levels of temperature – overheat and fire. /


sensitive |adjective| able to register very small differences or changes in conditions / Oscillating outputs from the alternators could cause sensitive equipment to malfunction or trip off. The actuator is sensitive to engine rpm. /


sensitivity |noun| the quality or state of being able to register very small differences or changes in conditions / Monitors detect disturbances which are below the sensitivity level of the gyros. /


sensor |noun| a device which receives and responds to a signal or stimulus / The inlet pressure is sensed by a single pitot-type sensor probe which is situated just in front of the compressor. /

sensory memory |noun| a memory of visual, auditory or tactile (touch) impressions

separate |adjective| existing as an independent thing / Propellers consist of a number of separate blades mounted in a hub. / - |verb|  1. to set or keep apart / Dry chemical extinguishers separate the oxygen element from the fire thus retarding combustion.2. to maintain a safe distance between aircraft. An aircraft in difficulty will need more airspace; manoeuvring may be slower and more difficult; the crew need to be able to concentrate on handling the failure and not on possible conflicts with other aircraft / ATC must separate the aircraft in distress from other traffic. /


separation |noun|  1. the condition of being spaced apart  2. the removal of something from a mixture or combination / The oil and air mixture flows over the de-aerator tray in the oil tank, where partial separation takes place. /


separation standards |plural noun| internationally agreed minimum separation limits for aircraft in flight


separator |noun| a device which removes something from a mixture or combination / The water separator will extract a percentage of free moisture from the air. /


sequence |noun| a series of things or events which follow one another, an order / The ignition system provides a rapid series of sparks timed to fire in each cylinder in the correct sequence. /


sequence valves |plural noun| a fluid flow controller which performs a number of actions in a particular order / Sequence valves are often fitted in a landing gear circuit to ensure correct operation of the landing gear doors and actuators. /

sequencing |noun| an air traffic controller’s action placing aircraft in order with a safe separation during approach

series |noun| a number of things or events which come one after the other in a particular order / a series of photographs, a series of switches /


series circuit |noun| an electric circuit connected so that current passes through each component of the circuit in turn without branching


serious |adjective| important, or giving cause for great concern or worry - serious damage > very bad damage - serious injury > very bad injury


serve |verb|  1. to act or to function as / In some aircraft, pressure gauges also serve as a maintenance check on leakage. /  2. to be used for a purpose / Different color-coded warning lights serve to alert the observer that something is wrong with the system. /


service |noun|  1. a facility / A pressure reducing valve is often used to reduce main system pressure to a value suitable for operation of a service such as the wheel brakes. /  2. work done for others as a profession / Cabin crew provide a commercial service to passengers. /  3. maintenance or repairs carried out - |verb| to do maintenance or repairs on / Jet engines are simpler to dismantle and service than piston engines. /


serviceability |noun| the ability to function as required / When carrying out engine checks, it is usual to turn off the magnetos in turn to check their serviceability. /


serviceable |adjective| able to function as required / The pilot must make sure that the radio equipment is serviceable prior to take-off. /


service area |noun| area where maintenance and repairs are carried out


service bay |noun| a space in the structure of an airplane where equipment can be located for maintenance or repairs / In most modern aircraft a number of the major components are grouped together in a hydraulic service bay which is easily accessible for routine servicing operations. /


service bulletin |noun| a notice issued by the manufacturer of an aircraft, engine or other equipment to alert people to problems with that equipment. Abbreviation: SB


servicing |noun| the action of carrying out maintenance and repairs / Accessibility of components and equipment during servicing enables work to be done more quickly. /


servo |abbreviation| servo-mechanism


servo-assisted |adjective| partially operated by a servo-mechanism / servo-assisted brakes, servo-assisted steering /


servo-control unit |noun| a unit, a combined selector valve and actuator, which moves a control surface / A servo-control unit is part of the system which relieves the effects of aerodynamic forces on the flight controls. /


servomechanism |noun| a device to convert input forces into much larger output forces / Two phase motors are normally used for very small or miniature motors in servomechanisms. /


set |noun| a group of things which belong together / a set of instruments, a set of figures / - |adjective| fixed or established / a set procedure / - |verb|  1. to adjust to a particular point or figure / The aircraft receiver is set to the required frequency. /  2. to put in a particular position / Set the throttle fully closed. /  3. to harden / The resin sets. / (NOTE: setting – set) - cold setting materials > materials which do not need heat to harden


set down |verb| to land an aircraft, or land somewhere in an aircraft


setting |noun|  1. a particular figure or position which a device is adjusted to - altimeter setting > adjustment of the sub-scale of the altimeter to read QFE, QNH, etc.  2. the action of adjusting a device to a particular position, etc. / The setting of the altimeter is done prior to take-off. /


settle |verb| to move into a final position / When wheels are first fitted to an aircraft, the tires tend to move slightly as they settle down on the rims. /


several |adjective| a number of but not many, more than a few / There are several types of instrument landing systems (ILS) in use. / - several minutes > a number of minutes


severe |adjective| extreme or intense (NOTE: Generally speaking, weather conditions can be described as light, moderate or severe, depending on the amount or intensity of the condition.) - severe icing > bad icing - severe turbulence > violent turbulence


severity |noun| the amount, intensity or seriousness of a condition / When the wind is strong the vertical currents become quite vigorous with the resultant increase in the severity of turbulence. /


SFAR |abbreviation| Special Federal Aviation Regulation


shade |noun|  1. intensity or richness of color / Shades of color of the landscape become lighter in misty conditions. /  2. cover or shelter from the sun / Surface air temperature is the temperature recorded in the shade at a height just above ground level. /


shadow |noun| an area which is not affected by full radiation because of partial or full blocking of rays by something between the area and the source of the radiation / Solar radiation does not exist at night when the rotation of the Earth creates a shadow zone from the sun. Line-of-sight transmission path means that obstacles and terrain can create shadow zones. /


shaft |noun| a long, generally cylindrical bar, especially one that rotates and transmits power / engine drive shaft, propeller shaft /


shaft horsepower |noun| the unit used for stating the power delivered to the shaft of a turbo-shaft or turboprop engine. Abbreviation: SHP


shaker |noun| a device which shakes or vibrates violently / Large aircraft use a stick shaker to supplement the natural stall warning of buffet. /


shallow |adjective| not deep - shallow angle > small angle


shallow depression |noun| an area of slightly low relative atmospheric pressure

shallow mist |noun| a thin layer of mist near the ground, usually in the early morning, above which the aircraft climbs quickly. Abbreviation: MIBR (French > mince brume)

shape |noun| form / The shape of an aircraft is determined by the requirement to provide an aerodynamic lift force great enough to support the weight of the aircraft and payload whilst in flight. /


sharp |adjective|  1. thin and capable of cutting or piercing / If a piece of thermosetting plastic is hit hard enough, it breaks into pieces with straight sharp edges. /  2. clear / The sharp setting means the bandwidth is reduced to 1kHz (kilohertz) to minimize noise or interference. /  3. clear and distinct / Cumulus clouds have sharp outlines. /  4. sudden and acute - a sharp increase > a sudden large increase


shatter |verb| to break into a number of pieces when hit / Clear ice is hard to shatter and break off. /


shear |verb| to break by lateral movement


shearing load |noun| load caused by sliding apart the layers of a structure


shear stress |noun| stress that occurs in riveted and bolted joints when a force causes one layer of material to slide over an adjacent layer


shed |verb| to get rid of / Non-essential loads may need to be shed in order to reduce weight. /


sheet |noun|  1. a large, thin, flat piece of material  2. a relatively large piece of paper - instruction sheet > a piece of paper on which special instructions are written or printed


shell |noun| the outer covering of something such as an aircraft fuselage


shield |noun| a protective covering / heat shield / - |verb| to protect by covering / The beacon should be sited on the highest ground to prevent the transmitted signal from being shielded. /


shift |noun|  1. movement from one place to another / a shift in position /  2. a change / When a radio transmission is made from a moving platform, there will be a shift in frequency between the transmitted and intercepted radio signals. /  3. a period of working time / The next shift is ready to take over. / - shift handover > the moment one group of controllers is replaced by another or one control center passes control to another - |verb| to change the position of something / to shift a load /


shock |noun|  1. a sudden violent impact / On all undercarriages some form of accepting the shock of landing must be included. /  2. disturbance of mental functions caused by a terrible experience or injury / Crew should be aware of reverse panic, a form of shock which makes passengers unable to comprehend the need for urgency. /


shock absorber |noun| device to minimize the shock to the main structure of the aircraft when it lands


shock wave |noun| compression wave caused by supersonic motion / As sonic speed is approached, the efficiency of the intake begins to fall, because of the formation of shock waves at the intake lip. /


shore |noun| a stretch of land at the edge of the sea or a lake, etc. / At a height of 3,000 feet it was possible to see the shore. /

short circuit |noun| an inadvertent electrical connection which can cause an electrical failure, a circuit breaker to open or an electrical fire

short final |noun| the last part of the approach before touchdown, typically from the inner marker, or some 2 nautical miles, to the threshold

shorten |verb| to make short or shorter in length or duration / Mishandling of aero-engines during operation can cause considerable damage and wear which can shorten the life of the engine. The length of the mercury column shortens when cooled. / Opposite: lengthen

shortly |adverb| soon, in a short time / We will be landing shortly. /

short-haul |adjective| traveling over a short distance


short-haul flight |noun| a flight over a short distance, up to 1,000km / On short-haul flights, passengers are usually offered only light meals. /


short-term conflict alert |noun| a ground-based safety net intended to assist the controller in preventing collision between aircraft by generating …an alert of a potential or actual infringement of separation minima


shot |noun| a discharge / Extinguishing of a fire in an auxiliary power unit (APU) compartment is normally done by a single-shot fire extinguisher. /


shower |noun| a short period of rain or snow / Showers are forecast for the evening. Snow showers are expected in the area. /


SHP |abbreviation| shaft horsepower


shroud |noun|  1. an extension of a fixed surface of a wing towards the rear, which covers the leading edge of a movable surface hinged to it  2. any one of the lines by which the harness of a parachute is attached to the canopy


shunt |noun| a low-resistance connection between two points in an electric circuit that forms an alternative path for a portion of the current / The shunt-wound generator, used in conjunction with a voltage regulator, is the most common type of DC (direct current) generator system for aircraft. / Also called: bypass

shutdown |noun| the act of reducing engine or APU power to zero, stopping engine operation

shutter |noun| a hinged door which controls the flow of air / oil cooler shutters, radiator shutters /


SID |abbreviation| standard instrument departure, a pre-planned, coded ATC IFR departure routing


side-stick controller |noun| a small side-mounted control column used on aircraft such as the Airbus A340


sight |noun|  1. view / The fog cleared and the mountain came into sight. /  2. - with the airfield in sight > a transmission to air traffic control to confirm that the pilot can see the landing airfield  3. the ability to see using the eyes - |verb| to see something when it is a long way away / Sea marker dyes can only be used once and should only be used when a search aircraft is sighted. /


sight glass |noun| a simple fluid-level gauge


SIGMET |abbreviation| significant meteorological information


sign |noun|  1. a small quantity or amount of a something which may suggest the existence of a much larger quantity / Any sign of smoke or fire outside a wing exit means it cannot be used. /  2. a display with letters and/or numbers, sometimes lit up / the ‘fasten seat belt’ sign, ‘no-smoking’ sign /  3. a symbol such as: -, +, x or ÷, which represents an operation - |verb| to put one’s signature on a document, a letter, etc. / Remember to sign the letter. /


signal |noun|  1. a device, action or sound which passes information  2. a radio wave transmitted or received / As a general rule, radio signals travel in straight lines. /


signals area |noun| an area on an aerodrome used for displaying ground signals


signals mast |noun| a vertical pole on an airfield from which signal flags are flown


signals square |noun| an area on an aerodrome from which ground signals are displayed


signature |noun| the name of a person written in a special way to show that a document has been authorized or to show who is the author of a letter, etc. / Look at the signature to see who wrote the letter. /


significance |noun| importance / Except near a coastline where the sea breeze may augment the up-slope motion, anabatic winds are of little significance. /


significant |adjective| important and therefore noticeable / The vertical currents and eddies formed by the flow of air over hills and mountains have a significant effect on aircraft encountering them. /


significant meteorological information |noun| a weather advisory concerning weather conditions important to the safety of all aircraft, such as severe or extreme turbulence. Abbreviation: SIGMET


significant points |plural noun| geographical positions used in air navigation, which are defined by latitude and longitude and have names consisting of five letters


significant weather chart |noun| a weather chart with important weather information marked on it


signify |verb| to indicate, to suggest, to mean / Buffet signifies the approach of a stall. / (NOTE: signifies – signifying – signified)


silence |noun| the absence of sound - total silence > the complete absence of sound - |verb| to stop, or stop something, making a noise / When an engine fire warning is received on the flight deck, the first action should be to silence the warning bell. /


silencer |noun| a device to reduce noise / In order to reduce the level of noise from the blower, silencers are incorporated in the main supply ducting. /

sill |noun| a lower part of the doorway / The door sill scuff plate was slightly damaged by the catering truck. /

similar |adjective| nearly the same / Turbo-shaft engines are similar to turboprop engines. /


similarity |noun| the fact of having features that are nearly the same / There are points of difference and similarity between the two aircraft. /


simple |adjective|  1. basic, not complex / A simple fuel system consists of a gravity feed tank, a filter, a shut-off valve and pipes. /  2. easy


simplicity |noun| the quality of having a basic, uncomplicated design or concept / Because of its lightness, cheapness and simplicity, a fixed pitch propeller is often fitted to single-engine aircraft. /


simplify |verb| to make easy, to make less complex or complicated / Repair procedures are being further simplified by increasing use of cold setting resins. /


simulate |verb| to imitate the conditions or behavior of something / The computer program simulates the action of an aircraft. /


simulated instrument flight |noun| an instrument flight carried out in a simulator on the ground or in a specially prepared aircraft with screens on the windows


simulation |noun| an imitation of a real situation, created often for training purposes / The computer animation showed a simulation of the events which followed the explosion on board the aircraft. /


simulator |noun| a machine that is constructed to look like an aircraft cockpit with a full set of instruments, in which people can be trained to fly a particular type of aircraft


simultaneous |adjective| happening at the same time / Most aircraft are now fitted with remote magnetic indicator displays which can be selected to show two simultaneous bearings from different radio-navigational aids. /


sine |noun| a trigonometric function defined as the length of the side opposite to an angle in a right-angled triangle divided by the length of the hypotenuse. Abbreviation: sin


single |adjective| one only


single-engined aircraft, single-engine aircraft |noun| an aircraft with one engine only


sink |noun| a downdraft of air - rate of sink > the rate of descent of a glider / In order to achieve a safe landing, a glider has to be controlled so that it makes contact with the runway smoothly at a very low rate of sink. / - |verb| to move downwards as in a fluid / If water enters the fuel tank, it will sink to the bottom of the tank where it can be drained off. /


sit |verb| to be resting with your behind on a seat such as a chair / The pilot sits in the cockpit. / (NOTE: sitting – sat)


site |noun| a selected area of land / landing site / - |verb| to position or to put in a particular place /Where it is impossible or inadvisable to site the localiser antenna on the runway center-line, it may be positioned to one side./


sitting |adjective| - sitting position > the position of a person who is on a seat / The correct technique of using the escape slides is to assume a sitting position. /


situate |verb| to put in a particular place, to locate / The inlet pressure is sensed by a single pitot-type probe which is situated just in front of the compressor. /


situation |noun|  1. a location, the place where something is / The situation of the flight controls is important. /  2. the conditions or circumstances in a particular place or at a particular time / The synoptic chart is a graphical representation of the general weather situation over a given area at a given time. /


six character group |noun| a group of six letters and/or numbers


six degrees of freedom of motion |plural noun| the six types of movement that an aircraft must be able to make: forward, upward and downward, and roll, yaw and pitch


size |noun| the extent of a thing, how big something is / Whether or not an object can be seen by aircrew at a given distance will depend on factors such as the size, shape and color of the object. /


skid |noun|  1. a slide on slippery ground / Anti-skid braking systems units are designed to prevent the brakes locking the wheels during landing, thus reducing the possibility of wheel skid. /  2. a condition of uncoordinated flight then the aircraft moves away from the center of a turn / Deflection of the ball in the turn coordinator indicates a slip or a skid. / (NOTE: To correct a skid, the pilot should increase the bank, or increase rudder pressure on the same side as the ball has moved to in the turn coordinator.) - |verb|  1. to slide on slippery ground / If you brake too hard on a wet surface, you might skid. / (NOTE : skidding – skidded) - to skid to a halt > to slide or skid until you stop  2. to move sideways towards the outside of a turning maneuver


skill |noun| expertise, an excellent ability in something / Skill in accurate flying can only be achieved by constant practice. /


skin |noun| the outer layer of a body, or the outer layer of an aircraft / The aircraft skin is riveted to stringers and frames. /


skip distance |noun| the shortest distance at which a sky wave can be received / The higher the layer in which a direct wave signal is totally refracted and returns as a sky wave, the greater the skip distance. /


ski-plane |noun| an aircraft equipped with skis for taking off from and landing on snow


sky |noun| the atmosphere and outer space as seen from the earth / The higher the sun is in the sky, the more intense is the radiation per unit area. /


skyjack |verb| to use force to take illegal control of an aircraft, especially a commercial aircraft, when it is in the air


sky wave |noun| part of a radiated wave which is returned to Earth by refraction from the ionosphere


sky-way |noun| a route used by aircraft


skywriting |noun|  1. the use of an aircraft releasing colored smoke to form letters in the sky  2. letters or a message formed in the sky by colored smoke released from an aircraft


slack |adjective|  1. not tight - a slack cable > a loose cable  2. not busy / Early afternoon is a slack period of the day. /  3. widely spaced /Throughout the tropics and sub-tropics, where pressure gradients are normally slack, the sea breeze is a regular feature. Land and sea breezes occur in coastal areas when there is a slack pressure gradient./


slant |noun| a slope or inclination / Distance Measuring Equipment (DME) is a radio aid which measures aircraft slant range to a ground beacon. / - |verb| to slope / The wing slants upwards from the root to the tip. /

slant visibility |noun| the fact of seeing something at an angle rather than head on which causes distortion

slat |noun| a movable device on the leading edge of a wing which, when extended, creates a gap that allows air to pass smoothly over the top of the wing thus reducing the possibility of a stall / The Socata Rallye is one of the few light aircraft with leading edge slats. /


sleet |noun|  1. melting snow or a mixture of rain and snow falling together  2. US frozen rain in the form of clear drops of ice or glaze ice covering surface objects (NOTE: Care should be taken to avoid any ambiguity.) - |verb| to fall in the form of sleet / It is sleeting. /


slide |noun| a device which allows continuous movement over a smooth surface - |verb| to move continuously over a smooth surface / Shear stress is the stress that resists the force tending to cause one layer of a material to slide over an adjacent layer. / (NOTE: sliding – slid)


slide raft |noun| an escape slide which, when detached from the aircraft, can be used as a life-raft


slide rule |noun| a graduated device with sliding parts for performing complex mathematical operations


slight |adjective| small, minor - a slight increase > a small increase - a slight drop in temperature > a small decrease in temperature


slip |noun| a condition of uncoordinated flight when the aircraft moves towards the inside of a turn / Slip is indicated by deflection of the ball in the turn and slip indicator. / - |verb| to move sideways towards the inside of a turning maneuver as a result of excessive bank (NOTE: To correct a slip, the pilot should decrease the bank, or increase rudder pressure on the same side as the deflected ball in the turn coordinator. Slips are often used in aircraft with no flaps to increase the rate of descent without increasing the airspeed.)


slippery |adjective| which is difficult to grip firmly because of wetness, smoothness, etc. / a slippery surface such as a wet or snow-covered runway /


slip-ring |noun| a metal ring in a generator to which current is delivered by the brushes


slipstream |noun| the flow of air sent backwards by an aircraft’s propeller


slope |noun|  1. a slanting surface or slanting piece of ground, an incline / A slope of the runway may increase or decrease the take-off and landing runs. /  2. a state in which one end of an aircraft is higher than the other - |verb| to be inclined, to be at an angle / When the runway slopes upwards, away from the aircraft, the approach may appear to be higher than it actually is. /


slot |noun|  1. a groove or channel into which something can be fitted / The float engages with a slot cut in the tube, so that, as the fuel level changes, the float moves up and down. /  2. the particular time at which an aircraft is scheduled to depart / Flight GF 506 missed its slot and will have to wait 45 minutes for another. /


sm |abbreviation| statute mile


smog |noun| a mixture of smoke and fog / Smog is now rare because of pollution control. /


smoke |noun| a white, grey or black product formed of small particles given off by something which is burning / The weather associated with visibility reductions by particles suspended in the atmosphere is classified either as fog, mist, haze or smoke. / - |verb|  1. to give off smoke / Somebody noticed that one of the engines was smoking. /  2. to breathe in smoke from a cigarette, cigar, etc. / Passengers are not allowed to smoke in the toilets. /


smoke alarm |noun| a warning system that will ring or light up if there is smoke somewhere / Washrooms are fitted with smoke alarms. /


smoking |noun| the act of breathing in smoke from a cigarette, cigar, etc. - the airline has a no-smoking policy > the airline does not allow passengers to smoke during a flight


smooth |adjective|  1. even and without lumps or dents / a smooth surface /  2. not rough or turbulent / High ground will disturb the smooth, horizontal flow of air. / Opposite: rough - a smooth running engine > an engine which is operating well


SMR |abbreviation| surface movement radar


snap roll |noun| a maneuver in which an aircraft turns a complete circle longitudinally while maintaining altitude and direction of flight


snow |noun| atmospheric water vapor frozen into ice crystals and falling to Earth as white flakes / Snow cover tends to persist on north-facing slopes of mountainous regions after it has melted on south-facing slopes. /

snow blower |noun| a vehicle which clears runways of snow by blowing

snowfall |noun| a quantity of snow which comes down at any one time / a heavy snowfall /


snowflake |noun| a small piece of snow formed from a number of ice crystals / The size of a snowflake depends on the temperature. /

snow flurries |noun| a sudden and rapid falls of snow

snowplough |noun| a vehicle built to push the snow from roads, tarmac, etc.


snowstorm |noun| a heavy fall of snow accompanied by wind / The airport is closed because of the snowstorm. /


soft |adjective| not hard / Thermoplastic materials become soft when heated. /


soften |verb| to make soft / Thermoplastic materials are softened by many aircraft fluids. /


solar |adjective| referring to the sun


solar-powered |adjective| powered by energy derived from the suns rays


solar radiation |noun| the total electromagnetic  radiation given off by the sun


solid |adjective|  1. referring to something which is not liquid or gaseous / Visibility is reduced by the presence of solid particles such as dust or sand in the atmosphere. /  2. - solid line > unbroken line - |noun| a substance which is not a liquid or a gas / Ice is a solid, water is a liquid and vapor is a gas. /


solid-state |adjective| referring to semiconductor devices


solid-state device |noun| an electronic device that operates by using the effects of electrical or magnetic signals in a solid semi-conductor material


solid-state technology |noun| technology using the electronic properties of solids to replace those of valves


solo |adverb| done by one person alone / He flew solo across the Atlantic. /


solution |noun|  1. an answer to or means of solving a problem or difficulty / The navigation computer or slide rule is suitable for the solution of many different types of mathematical problem. /  2. a liquid made by dissolving a solid or gas in water or some other fluid / Spillage from a lead acid battery may be neutralized by washing with a dilute solution of sodium bicarbonate. /


solve |verb| to find the answer to, or a way of removing, a difficulty or problem / The triangle of velocities is used to solve navigation problems. /


somewhat |adverb| to some extent, a bit / The usefulness of pure aluminum as a structural material is somewhat limited. /


sonic |adjective|  1. referring to sound  2. within the human hearing range - sonic speed > the speed of sound


sonic boom |noun| a noise, due to shock waves, produced when an aircraft travels through the air faster than the speed of sound


sophisticated |adjective| highly developed and complex / The electronic flight instrument system, commonly known as EFIS, is a highly sophisticated type of flight director system. The A340 is a sophisticated airplane. /


sortie |noun| an operational flight by one aircraft / The test program has accumulated 1,146 sorties. /


sound |adjective| strong / A stressed skin structure is used on modern aircraft which gives a sound structure with relatively low weight. / - |noun| something that can be heard and is caused by vibration of the surrounding air / FM (frequency modulation) gives a wide range of sounds or a very high data rate. / - |verb|  1. to make a noise / If the trim position is incorrect, a warning horn will sound when number three thrust lever is advanced for take off. /  2. to seem / It sounds as if the pilot is having trouble. /


source |noun| a supply / Under emergency conditions, the battery may be the only source of electrical power. Jet aircraft have a ready source of compressed air from the compressor sections of their engines. /


south |noun| a compass point on the mariner’s compass 180° clockwise from due north and directly opposite north / Fly towards the south. / - south facing mountain side > the face of a mountain which looks towards the south - |adjective|  1. referring to areas or regions lying in the south, referring to the compass point 180° from north / the south side of the river /  2. the southern part of a region or country / South America, South Dakota / - |adverb| towards the south / The aircraft is flying south. /


southbound |adjective| traveling towards the south / a southbound flight /


south-east |noun| the direction between south and east / a region in the south-east of Canada / - |adjective|  1. situated in the south-east / the south-east coast of England /  2. blowing from or coming from the south-east - |adverb| towards the south-east / We were heading south-east. /


south-easterly |adjective|  1. blowing from or coming from the south-east / a south-easterly wind /  2. moving towards the south-east / We were following a south-easterly direction. /


south-eastern |adjective| referring to or situated in the south-east / the south-eastern coast of Spain /


southerly |adjective|  1. situated towards the south / the most southerly point of a country /  2. coming from the south / A southerly wind was blowing. /  3. moving to or towards the south / We were flying in a southerly direction. / - |noun| a wind which blows from the south


southern |adjective| situated in the south / the southern hemisphere, the southern Atlantic /


southern hemisphere |noun| the area of the Earth to the south of the equator


South Pole |noun| the point which is furthest south on the earth / to fly over the South Pole /


southward |adjective| going towards the south / to go in a southward direction / - |adverb| US same as southwards


southwards |adverb| towards the south / The aircraft was flying southwards. /


south-west |noun| the direction between south and west / a region in the south-west of France / - |adjective|  1. situated in the south-west / the south-west tip of England /  2. blowing from or coming from the south-west - |adverb| towards the south-west / We were heading south-west. /


south-westerly |adjective|  1. blowing from or coming from the south-west / a south-westerly wind /  2. moving towards the south-west / We were following a south-westerly direction. /


south-western |adjective| referring to or situated in the south-west / The south-western corner of England includes Cornwall and Devon. /


south wind |noun| a wind blowing from or coming from the south (NOTE: A wind is named after the direction it comes from.)


space |noun|  1. an empty area / A major problem with fuel storage is finding space within the airframe. /  2. the physical universe outside the Earth’s atmosphere / VHF (very high frequency) waves tend to pass through the layers of the ionosphere into space. /

spacing |noun| a safe distance between aircraft / A key role of an ATCO is to maintain spacing at all times. /

span |noun| the distance between two points


spar |noun| the main longitudinal beam of an aircraft wing / Designing a wing skin, a rib or a spar as a single big item rather than assembling it from many smaller components minimizes the number of structural parts. /


spark |noun| a light produced by a sudden electrical discharge - |verb| to suddenly start a process or action / Crew must quickly establish control to ensure panic does not spark a premature evacuation. /


spark plug, sparking plug |noun| a device screwed into each cylinder head in spark ignition engines, which initiates fuel combustion by an electric spark. Also called: sparking plug


spat |noun| a streamlined covering for a wheel fitted on a light aircraft to reduce drag. Also called: wheel fairing


spatial disorientation |noun| a situation of bad visibility and/or unusual maneuvers which result in the pilot not knowing what attitude the aircraft is in


speaker |noun| - loud-speaker


special |adjective| particular, specific, or not ordinary / To make a composite, it is necessary to combine the reinforcing glass fibers with some form of special glue. / - |noun| a special meteorological report


special aerodrome report |noun| report used if there are significant weather changes since the last meteorological aerodrome report. Abbreviation: SAR


special VFR flight |noun| a controlled VFR flight permitted by air traffic control to fly within a control zone in meteorological conditions below visual meteorological conditions


specific |adjective| clearly defined and definite / Flight levels are specific pressure altitudes. The airframe has to be built to very specific requirements. /


specification |noun| a detailed description that sets out what something consists of, what is needed, what is involved, etc. / Fluids are colored for recognition purposes and fluids of different specifications must never be mixed. /


specific gravity |noun| the density of a substance compared with that of water, which is 1.00 (NOTE: This is the old name for relative density.)


specify |verb| to name in detail / The minimum values for decision heights are specified by the national licensing authorities for various types of aircraft and for various airports. Pressure must be maintained within specified limits during all phases of flight. /


specimen |noun| a part taken as an example of the whole / By testing specimen structures and components to destruction a safe life can be assessed for all such structures and components. /


speed |noun| the rate of motion over a distance in time

Speedbird |noun| the call-sign for British Airways

speed-brakes |noun| upper wing flight control surfaces, or spoiler function, which decrease airspeed in flight

speed bugs |noun| a small plastic markers, now often replaced by digital displays, which are set manually or automatically around / along the airspeed indicator scale to give the crew easily visibly references to critical airspeeds during take-off and approach: V1 or decision speed, when the pilot must decide to take off or reject take-off; V2 take-off safety speed at which the aircraft can be safely airborne with one engine shut down; various flap retraction / extension speeds; Vref, final approach speed. They are also referred to as V-bugs.

sphere |noun| an object in the shape of a ball / The Earth is not a perfect sphere. A circle drawn on the surface of a sphere, whose plane passes through the center of the sphere is called a great circle. /


spherical |adjective| shaped like a sphere / The Earth is almost spherical in shape. Drain cocks are generally simple, manually operated spherical valves. /


spill |noun| the running out of a liquid from a container, especially when it is unintentional / an oil spill, a fuel spill / - |verb| to cause liquid to run out of a container, usually unintentionally / If fuel gets spilled, it creates a fire hazard. / (NOTE: spilling – spilled)


spillage |noun| the spilling of a liquid / Any fuel spillage must be cleaned up immediately. / (NOTE: The word spillage is used in a more general sense than the word spill.)


spin |noun|  1. fast rotation / the spin axis of the earth /  2. the continued spiral descent of an aircraft where the angle of attack of one wing is greater than the stalling angle - |verb|  1. to rotate rapidly / The Earth is spinning on its axis. /  2. to put an aircraft into a continued spiral descent with the angle of attack of the main-plane greater than the stalling angle / It is prohibited to spin general-purpose light aircraft which are not equipped with a suitable harness. /


spindle |noun| a pin or bar which rotates or on which something rotates / A cup anemometer has three cups, mounted on a spindle, that are driven by the wind causing the spindle to rotate. /


spine |noun| the longitudinal central part of an engine / Annular inner and outer air casings form a tunnel around the spine of the engine. /


spinner |noun| a cap that fits over the hub of the propeller of an aircraft


spiral |adjective| winding continuously in circles as it ascends or descends


spiral dive |noun| a dangerous uncontrolled turning descent of an aircraft in which rate of descent and speed increase


spline |noun| a groove in a shaft for meshing or engaging with another component


split |noun|  1. a division  2. a break along a line, especially in wood, plastic or rubber / a split in a tire / - |verb|  1. to divide / Retractable undercarriages can be split into three groups. /  2. to break along a line / One of the tires split on impact. / (NOTE: splitting – split) - |adjective| divided or broken along a line


split bus system |noun| an electrical system in which there are two separate power generation systems / The parallel system and the split bus system are both used to distribute electrical power. /

split sector |noun| a controlled airspace divided vertically (by flight level) or horizontally to accommodate high traffic, preferably using different radio frequencies

spoiler |noun| a hinged surface on the upper wing which, when opened, decreases lift and increases drag / If a problem occurs in the spoiler system a master caution light illuminates. / (NOTE: Spoilers are sometimes called ‘speed brakes’. They are used during the descent prior to landing and immediately after landing to decrease lift and increase braking effect.)


sponson |noun| an air-filled structure or small wing projecting from the lower hull of a seaplane to keep it steady on water


spontaneous |adjective| happening without external cause / Spontaneous ignition may occur if oxygen is allowed to come into contact with oil or grease. /


spool |noun| one complete axial-compressor rotor / The single spool compressor consists of one rotor assembly and stators. / - |verb| - to spool down > to allow the revolutions of a turbofan engine to decrease - to spool up > to increase the revolutions per minute of a turbofan engine


spot |noun|  1. a special or small place / Charts should be kept in a convenient spot in the cockpit. /  2. a small roundish mark or piece / a spot of oil on a shirt / - spot height > the height of a particular place, e.g. a mountain peak, marked on a chart


spotlight |noun| a powerful, often moveable light which illuminates a small area / A spotlight is mounted on the roof. /


spray |noun|  1. a body of liquid in fine drops / The generator is cooled by oil spray delivered by the constant speed drive section. /  2. a container that sends out liquid in fine drops - |verb| to apply or to send out liquid in the form of fine drops / Some engines have the coolant sprayed directly into the compressor inlet, but for axial flow compressor engines, it is more suitable to spray the coolant into the combustion chamber inlet. /


spread |noun| an extension of the area covered or affected by something / Measures are taken to prevent the spread of fire. / - |verb| to extend the area of something / Strong jets of water should not be used on a liquid fire as this may cause the fire to spread. The system sprays a quantity of fluid onto the windscreen, which is then spread by the wipers. / (NOTE: spreading – spread)


spring |noun|  1. a metal device which, when under tension, tries to resume its previous position / The pitch lock piston is held in the forward position by a spring. /  2. the season between winter and summer


squall |noun| a sudden increase in wind speed lasting for several minutes / Surface squalls are due to the spreading out of strong downdrafts at the surface. Even with a light mean wind speed, squalls of 50 kt(knots) or more can occur with sudden changes in direction. / Abbreviation: SQ


square |noun| a shape with 4 equal sides and 4 right angles - |adjective| shaped like a square / a square panel /


square foot |noun| a unit of measurement of area, which is one foot long by one foot wide


square meter |noun| a unit of measurement of area, which is one meter long by one meter wide / The room is 5m x 9m so the area is 45 square meters (45m2). /


square root |noun| divider of a quantity that, when multiplied by itself, gives the quantity / 3 is the square root of 9. /


squawk |noun| a transponder identifier code which enables an ATC to identify each aircraft on radar screens - |verb| to activate specific modes, codes or functions on a transponder / Garbling occurs when two signals are received simultaneously and can be resolved either technically or by making one of the aircraft squawk. /


squeeze |verb| to press hard from opposite directions / Static seals, gaskets and packing are used in many locations, and these effect a seal by being squeezed between two surfaces. /


SR |abbreviation| sunrise


SS |abbreviation| sunset


SSR |abbreviation| secondary surveillance radar


stabilize |verb| to become steady and unchanging / After the engine has been started, engine speed is increased to 1,000 r.p.m. (revolutions per minute) until cylinder head and oil temperatures have stabilized at normal operating temperatures. /

stabilized approach |noun| the course followed by an aircraft preparing for landing where the aircraft is on the glide-path at the correct airspeed, in the correct configuration (flaps, slats, gear) and where checklists have already been completed

stabilizer |noun| a device to improve the tendency of an aircraft to return to its original attitude after being deflected (NOTE: Some aircraft have an all-moving tailplane called a ‘stabilator’ (a combination of the words stabilizer and elevator).

stabilizer trim runaway |noun| a malfunction which occurs when the Trimmable Horizontal Stabilizer (THS), or tailplane, on the aircraft tail fails to stop at the selected position and continues to deflect up or down

stabilitator |noun| - stabilizer


stability |noun|  1. being stable or steady / The stability of the Cessna 150 makes it an ideal training aircraft. /  2. a state of the atmosphere in which air will resist vertical displacement / When air moves away from its source region, the stability of the lower atmosphere changes. / (NOTE: Stability can be classified as three types. Positive stability is the tendency of a body to return to its original state after being displaced. Light training aircraft have positive stability. Neutral stability is the tendency of a body to remain in the new position after displacement. Negative stability is the tendency of a body to continue moving away from its original position after displacement.)


stability augmentation system |noun| a flight control system which automatically adjusts pitch and yaw to improve an aircraft’s stability. Abbreviation: SAS


stable |adjective|  1. steady  2. referring to an atmosphere in which there is little or no vertical movement / Layer cloud occurs in a stable atmosphere. /


stack |verb|  1. to put one on top of the other / By stacking rows of horizontal dipoles one above the other, a well-defined electronic glide path can be transmitted. /  2. to keep aircraft circling at different heights while they are waiting to land at an airport - |noun| a number of aircraft waiting to land at an airport that are circling at different heights


stacked |adjective| circling at different heights prior to landing


stack-up |noun| same as stack


stage |noun|  1. one of several sections, steps, or levels into which a process can be divided / There are three stages in the life cycle of a thunderstorm: process of formation, development and decay. Calculate headings to steer for each stage of the flight. / - cruise stage of the flight > the section of a flight between top of climb after take-off and start of descent to land - at a later stage > at a later time  2. a group components forming part of an electrical or electronic system / In the axial flow compressor, many stages of moving and stationary blades are needed, each row of rotors and a row of stators forming a stage. /


stagger |noun| a design in which the leading edge of one wing of a biplane projects beyond that of the other wing - |verb| to make the leading edge of one wing of a biplane project beyond the leading edge of the other wing


stall |noun|  1. a loss of lift caused by the breakdown of airflow over the wing when the angle of attack passes a critical point / In some configurations it is possible for the buffet speed to be less than the required 7% margin ahead of the stall. /  2. a situation in which an engine or machine stops suddenly because an opposing force overcomes its driving power / Compressor stall can be caused by ice formation in the air intake. / - |verb| to lose lift by the breakdown of airflow over the wing when the angle of attack passes a critical point / Many light aircraft stall when the angle of attack exceeds 15°. / (NOTE: A stall has nothing to do with the engine stopping. An aircraft can stall at any airspeed and in any attitude.)


stalling angle |noun| the angle relative to the horizontal at which the flow of air around an airfoil changes abruptly, resulting in significant changes in the lift and drag of an aircraft


stalling speed |noun| the speed at which the angle of attack is such that lift over the wing surface breaks down (NOTE: Traditionally, an aircraft can stall at any airspeed, providing the angle of attack is great enough. Stalling speed is often used to refer to the speed below which the aircraft cannot remain airborne.)


stall warning system |noun| a system to warn the pilot that the aircraft is about to stall

stand |noun| a designated place at the ramp where aircraft are being serviced

standard |noun| something, e.g. a quality or measure, that is officially recognized as an example that others must conform with / Water is the standard for determining relative density. / - a high standard of skill > a high level of skill - |adjective| normal, officially or generally accepted - standard operating procedures > specific procedures defined by an airline to respond to all contingencies


standard atmosphere |noun| a unit of pressure defined as the pressure that will support a 760 mm column of mercury at 0°C at sea level, equal to 1.01325 x 10 5 newtons per square meter


standard instrument departure |noun| a published navigational chart showing the route an aircraft must take as it takes off and climbs away from an airport. Abbreviation: SID


standard parallels |plural noun| (in a conical projection) the parallels of latitude where the cone cuts the surface


standard pressure setting |noun| 1013.25 millibars. Abbreviation: SPS


standard rate turn |noun| a turn made at a precise number of compass degrees per second (NOTE: Rate 1 turn = 180 ° in 1 minute, Rate 2 turn = 360 ° in 1 minute, Rate 3 turn = 540 ° in 1 minute, Rate 4 turn = 720 ° in 1 minute. Standard rate turns are made using particular angles of bank for specific airspeed and are used while flying under Instrument Flight Rules (IFR). The pilot can make accurate turns to given headings by banking at the standard rate and timing the turn.)


standard time |noun| a universally adopted time for all countries based on zone time


standby |adjective| secondary, able to be used as a back-up / Some aircraft use a ram air turbine that can be very useful as a standby power source in the event of failure of a complete main AC (alternating current) generating system. /


standby ticket |noun| a cheaper air ticket bought just before departure time / There are no standby tickets to Montreal. /


standing agreement |noun| an agreement between controlling units in different flight information regions to allow the transfer of control from one sector to the next without individual coordination, provided agreed parameters are met


standing wave |noun| the motion of air downwind of a steep hill or mountain in which the high and low points of the wave do not move


STAR |abbreviation| standard arrival route


starboard |noun|,|adjective| the right-hand side of an aircraft when facing forwards when inside the aircraft / The angle between heading and track of an aircraft is called drift and is expressed in degrees to the port or starboard side of aircraft heading. / Opposite: port


starter |noun| a device to start an engine


starter motor |noun| in a piston engine, a small electrically operated device to turn the engine until ignition starts


start-up |noun| a procedure to start an engine / After start-up, the engine accelerates up to idling speed. /


state |noun| the existing condition of something / Ice in a liquid state is called water. Water in a gaseous state is known as vapor. A logic gate is a two-state device i.e. on/off. / - in a poor state > in a bad condition - |verb| to say or to mention, or to give information clearly / It states in the information that you must not open the can near a flame. Please state your name and address. /


statement |noun| something formally expressed in words / After the crash, the president and chief executive of the company made a brief statement to the waiting news reporters. /


static |adjective| not acting, not changing, passive or not moving - |noun| the background noise during radio transmission

static discharger |noun| an electrical conductor on the outer trailing edges of the wings and stabilizers designed to discharge static electricity which accumulates in the aircraft during the flight or as the result of a lightning strike. Also called: wick

static display |noun| a display of parked aircraft on the ground


static electricity |noun| electricity not flowing as a current / When the aircraft travels through the air, friction causes a charge of static electricity to be built up on the airframe. /


static ground running |noun| the running of the engine while the aircraft is stationary on the ground


static line |noun| a rope attached to an aircraft and a parachute that automatically opens the parachute when the parachutist jumps


static port |noun| a small hole in the side of the aircraft which senses static pressure and is used in the operation of the altimeter, vertical speed indicator and airspeed indicator / Ensure that the static port is clear. /


static pressure |noun| the pressure of a fluid acting on and moving with a body


station |noun|  1. a particular assigned location / The inter-phone system allows the flight deck to communicate with cabin crew stations. /  2. the location of a radio transmitter / a VOR station /


stationary |adjective| not moving / The aircraft was stationary on the ground with engine running. /


stator |noun| a fixed part of a rotary machine / The low-pressure compressor has large rotor blades and stator blades and is designed to handle a far larger airflow than the other two compressors. A temperature probe is embedded into the stator of the generator and a meter is provided, so that generator stator temperature can be monitored. /


status |noun| condition / The center-zero ammeter tells the pilot the status of the aircraft battery. /


statute mile |noun| a non-SI unit of length equal to 1.609 kilometers / It is 20 statute miles to the airport. / Abbreviation: sm


STC |abbreviation| supplemental type certificate


STCA |abbreviation| short-term conflict alert


steady |adjective| constant and unchanging / The manual test will give a steady red light. / - a steady wind > a wind of constant speed and direction


steam fog |noun| fog formed when cold air moves over relatively warm water / Visibility was impaired because of steam fog. /


steel |noun| a metal alloy of iron, carbon and other compounds - stainless steel > steel containing chromium and nickel that is highly resistant to corrosion / Tubing in parts of the system containing fluid at high pressure are usually made from stainless steel. /


steep |adjective|  1. sloping sharply - a steep angle of approach > the angle formed by the aircraft approach flight path and the horizontal is greater than usual  2. closely spaced  3. referring to marked changes in pressure or temperature in a relatively short horizontal distance / Cooling of the air in contact with the ground at night can cause a very steep inversion of temperature at the surface. Pressure gradients in anti-cyclonic curvature tend not to be steep. /


steer |verb| to direct by using a wheel or control stick / The aircraft is steered on the ground by using the rudder pedals. /


steering |noun|  1. guiding or directing / Steering is controlled by rudder pedals. /  2. a system for guiding or directing a car, aircraft, etc. / Most modern light aircraft have nose-wheel steering but older tail-draggers are steered on the ground by using differential braking. /


step |noun|  1. a stage / The first step in map reading is to orientate the chart. /  2. one stair / Mind the step! /

step climb |noun| gaining altitude by a series of steps, i.e. periods of level flight, between phases of climbing

step-down fix |noun| an identified point permitting descent in a segment of an ILS approach once an obstacle has been overflown

sterile cockpit |noun| a cockpit environment in which there are no audio or visual distractions from the piloting tasks / A sterile cockpit is one of the prerequisites of a safe working environment. /

steward |noun| a male member of airline staff who look after passengers during the flight. / cabin crew, flight attendant, stewardess / (NOTE: Different airlines use different terminology for their staff.)


stewardess |noun| a female member of airline staff who look after passengers during the flight 


stick |noun| the main hand control used by the pilot to control the aircraft roll and pitch / Using fly-by-wire technology, the stalling angle cannot be exceeded regardless of stick input. / - |verb| to become fixed, as if with glue / Ice crystals and snowflakes do not stick to airframes, and so icing is a problem only when super-cooled water droplets are present. /

stick shaker |noun| an aircraft stall warning system which when triggered by the angle of attack sensor causes the stick or control column to vibrate so that the pilot gives a nose-down order

sticking mike |noun| a microphone which is blocked in the open position

stiff |adjective|  1. rigid or inflexible / Kevlar 49 is stiffer than glass, but only about half as stiff as carbon fibers. /  2. not easily bent or turned - control surfaces may become stiff as a result of icing control > surfaces may become difficult to move  3. - a stiff wind > a fairly strong wind


stiffen |verb|  1. to make rigid or inflexible, to make stiff / Beams can be additionally stiffened in a downward direction by vertical and diagonal members. /  2. to become stronger


STOL |noun|  1. a flying system that allows an aircraft to take off and land on a very short runway  2. an aircraft fitted with the STOL system. Full form: short takeoff and landing


stop |noun|  1. the end of a movement - to come to a stop > to stop moving  2. a component which limits the distance that a moving part can move / An adjustable stop on the throttle control ensures a positive idling speed. /

stop bar |noun| a series of lights indicating whether access to a runway is authorized or not / Do not proceed if the stop bar lights are red. /

stopway |noun| an additional paved area beyond the normal end of the runway to allow for aircraft overrunning in an emergency

storage |noun| the act of storing something / A reservoir provides storage space for the system fluid. /


store |noun|  1. a supply / The maintenance section keeps a store of spare components. /  2. US a shop - |verb| to put away for future use / A capacitor is a device with the ability to temporarily store an electric charge. /


stores |plural noun| goods / Freight carrying aircraft have supporting members of greater strength to allow for the carriage of heavy stores. /


storm |noun| a violent weather disturbance with high winds and rain or snow / Storms produced by daytime heating are most frequently encountered in the afternoon and early evening. /


stow |verb| to place something in its correct position in the aircraft / Make sure the fire-extinguisher is stowed. /


stowage |noun| a space for stowing things / A multi-wheel combination has the advantage of smaller and lighter undercarriage structures, and wing stowage problems can be overcome by suitable mechanisms. /


stowaway |noun| a person who travels secretly by hiding in an aircraft, or a ship, not paying the fare / The crew must be alert at all times to the possibility of hijacking, bombs and stowaways. /

straight ahead |adverb| in a straight line, often on the extended runway center-line / Climb straight ahead. /

straight-in (approach) |noun| an instrument approach in which the final approach is begun without a prior procedure turn. In VFR, straight-in means the entry of a traffic pattern by interception of the extended runway center-line without executing any portion of a traffic pattern.

strain |noun| deformation caused by stress


strap |noun| a long narrow strip of fabric with a buckle - |verb| - to strap in > to fasten a seat or safety belt around somebody


strato-cumulus |noun| a layer of small cumulus clouds lower than alto-cumulus, i.e. below 3,000 m / Light rain may fall occasionally from strato-cumulus. /


stratosphere |noun| the layer of the atmosphere which extends from the tropopause to about 50 km above mean sea level / A cumulonimbus cloud may extend vertically, into the stratosphere. /


stratus |noun| a low-altitude layer cloud / Drizzle falls from shallow layer cloud such as stratus. /

stray |verb| to enter an area or airspace by mistake / The pilot was distracted and strayed onto the active runway. /

stream |noun| a steady current of a fluid / Thermocouple probes are positioned in the gas stream, so as to obtain a good average temperature reading. /


strength |noun|  1. the ability of a material to take pressure or support a load / Aircraft wheels require great strength and are constructed in two halves which are bolted together after the tire is fitted. Magnesium does not possess sufficient strength in its pure state for structural uses, but when mixed with zinc, aluminum, and manganese it produces an alloy having the highest strength-to-weight ratio of any of the commonly used metals. / - high-strength materials > materials which are very strong  2. the degree of clarity and volume of a signal / A radio wave loses strength as range increases. /  3. the degree of dilution of a liquid / Incorrect mixture strength may cause detonation. /  4. intensity of radiation / The strength of the sun’s radiation varies with latitude. /  5. the speed and force of a wind / High ground will disturb the smooth horizontal flow of air, with the degree of disturbance depending upon the strength of the wind and the roughness of the terrain. /


strengthen |verb| to make strong or stronger / Some alloys are hardened and strengthened by heat treatment. / - the wind is strengthening > the wind is increasing in speed


strengthening |noun|  1. the act of making stronger / Aircraft which require large apertures in the fuselage for freight doors, etc., need increased strengthening around these areas. /  2. the fact of becoming stronger / strengthening of the wind /


stress |noun|  1. the load per unit area to which a body that resists distortion or change of shape is subjected by internal forces / Turbine blades in the average jet engine vibrate at frequencies of 1 million per minute, and in each cycle experience stress. /  2. a worried, anxious and tired state brought on e.g. by overwork / He gave stress as the reason for wanting a week off work. /  3. emphasis - |verb| to emphasize / It must be stressed that the description is a model and departures from it often occur. /


stretch |noun| a continuous unbroken length / a stretch of coast / - |verb| to extend or enlarge beyond the proper limits / Tensile stress or tension is the resistance of a material to being stretched. /

stretcher |noun| a collapsible canvas bed for carrying an injured person / We will need a stretcher to carry off the injured passenger. /

stretching |noun| extending or enlarging beyond the proper limits / Tensile stress is the resistance to pulling apart, or stretching, produced when two forces in opposition act along the same straight line. /


strict |adjective| precise, exact / Fuels for aircraft must conform to strict requirements. All generator voltages, frequencies and their phase sequence must be within very strict limits to ensure proper system operation. /


strike |noun| an impact or collision - |verb| to hit (NOTE: striking – struck)


stringer |noun| a thin metal or wood strip which goes from one end of the fuselage to the other / Stringers are made of a light alloy material. /


strip |noun| a long narrow piece, usually of the same width from end to end / a strip of paper / - |verb| to dismantle / After the collision, the engine was stripped down to its component parts. /


stroke |noun| any of a series of movements of a piston from one end of the limit of its movement to another / The connecting rod links the piston to the crankshaft and transmits the force of the power stroke from the piston to the crankshaft. /


structural |adjective| referring to the structure of something such as an aircraft / As laid down in the flight manual, the structural limitations must never be exceeded. / - structural failure > a breaking of part of the aircraft structure


structure |noun|  1. something constructed / Aircraft structure serves the same purpose for an aircraft as the skeleton for a human body. /  2. framework


strut |noun| a bar or rod used to strengthen a structure against forces from the side / A strut is designed to withstand compressive loads. /


stub |noun| a short rectangular extension / The plan-form of a military air traffic zone is in the shape of a circle with a stub. /


sub- |prefix|  1. of less importance in rank  2. below


sub-beam |noun| a less important or minor beam / A lobe is one of two, four or more sub-beams that form a directional radar beam. /


subject |noun| a topic or matter for discussion or study / A knowledge and understanding of the subject of ice accretion is essential in order that the hazard can be minimized. /


subjected |adjective| - subjected to > affected by or made to experience something / To maintain the pressure difference between two internal engine sections, which are subjected to air pressures of different value, a multi-air seal is used. / (NOTE: There is an important difference between subject to and subjected to.)


subject to |adjective| likely to be affected by, liable to / The airspeed indicator is subject to error. Turbine engines are subject to icing during flight through super-cooled droplet cloud. / - |verb| - to subject to > to make something or somebody experience something, often something unpleasant / The aircraft was subjected to rigorous tests. /


sublimate |verb| to transform directly from the solid to the gaseous state or from the gaseous to the solid state without becoming a liquid / For hoar frost to form on an aircraft the airframe temperature must be below 0°C (Celsius), so that the surrounding air is cooled to below its dew point and water vapor in contact with the aircraft skin is directly sublimated into ice crystals. /


sublimation |noun| transformation directly from the solid to the gaseous state or from the gaseous to the solid state without becoming a liquid / In sub-zero conditions sublimation will occur when air is cooled below the frost point, producing a deposit of ice crystals. /


sub-scale |noun| a secondary, not main, scale on an instrument / The barometric pressure is set on the sub-scale and the altimeter main scale displays height or altitude. /


subsequent |adjective| following in time or order / A structural prototype is put through cycles of stressing far more severe than can be expected during the aircraft’s subsequent operational life. / - a subsequent occasion > a following occasion


subside |verb|  1. to sink to a lower level / Cool air subsides. /  2. to become less active or strong - the storm subsided > the storm grew quiet


subsidence |noun| the act of sinking to a lower level / Descending air occurs because of subsidence in the high pressure belts of the sub-tropics and poles. /


subsonic |adjective| flying at speeds slower than the speed of sound, or not designed to fly above the speed of sound


substance |noun| a material of a particular sort / Specific heat is the amount of heat required to raise the temperature of a substance by 1°C (Celsius) compared to the amount of heat required to raise the temperature of water by 1°C. /


substantial |adjective| considerable, important - substantial damage > a lot of damage - substantial increase > a big increase


subtend |verb| to be opposite to and delimit / The angle subtended by an arc equal to one 360th part of the circumference of a circle is called 1°(degree). /


subtract |verb| to deduct or to take away / 6 subtracted from 10 equals 4 (10 – 6 = 4). /


subtraction |noun| the operation of taking away or deducting / The major arithmetic operations are addition, subtraction, multiplication and division. /


subtropical |adjective| referring to the areas between the tropics and the temperate zone / In winter, the subtropical high retreats and gives way to cyclonic pressure patterns. /


sub-zero |adjective| below zero degrees / In sub-zero conditions sublimation will occur when air is cooled below the frost point, producing a deposit of ice crystals. /


success |noun| the achievement of something wanted / The key to success in navigation is pre-flight planning. /


successful |adjective| satisfactory, as wanted / His second attempt at landing was successful. /


succession |noun| the process of following in a particular order / A succession of minor incidents created a more serious situation. /


successive |adjective| following one after the other without interruption / All aircraft remained grounded for three successive days because of fog. A day is the period between successive transits of a meridian by the sun. /


such |adjective|  1. of this kind / An example of such a chart is shown on page 3. /  2. of a large enough extent or amount / The height of the cabin floor to the ground on large jet transports is such that serious injuries can occur by exiting through the doors when steps or ramps are not available. /


suction |noun| a force that causes a fluid or solid to be drawn into a space because of the difference between the external and internal pressures / In a fuel injection system, fuel is induced into the inlet port or combustion chamber by a pump rather than the suction caused by the venturi of a carburetor. /


sudden |adjective| immediate and without warning / a sudden drop in temperature /


suffer, suffer from |verb| to be affected by, to experience / Piston engines suffer from icing in moist air when the ambient air temperature is well above 0°C (Celsius). /


sufficient |adjective| enough / During pre-flight checks, the pilot must ensure that there is sufficient fuel for the flight. /


suffix |noun| an addition to the end of a word creating a new word / Apart from cirrus and stratus, which are complete names, all layer cloud names consist of a prefix according to height of base, and a suffix according to shape. / (NOTE: In the word cloudless , -less is the suffix meaning without.)


suggest |verb|  1. to indicate a possibility / A strong cloud echo on radar suggests that hailstones are present. /  2. to mean, to imply / Heap clouds, as the name suggests, often have great vertical extent. /


suit |verb| to meet the requirements of / On some engines, the ignition can be varied as the engine is running and is moved to suit the engine speed and load. /


suitable |adjective| appropriate or right for a particular purpose / Taking into account the limits imposed by aircraft performance, a suitable route must be chosen. /


sulfur |noun| US same as sulphur


sulfur |noun| a yellow non-metallic chemical element / Turbine fuels tend to corrode the components of the fuel and combustion systems mainly as a result of the sulfur and water content of the fuel. / (NOTE: The atomic number of sulfur is 16.)


sum |noun| the result of two or more numbers added together / When the component velocities act in the same direction, the resultant velocity is equal to the sum of their speeds in that direction. /


summarize |verb| to present something in a shortened, concise form / The effects of ice deposits on aircraft can be summarized as follows …. /


summary |noun| a brief account of something more detailed / At the end of each chapter there is a summary. /


sump |noun| the oil reservoir of a piston engine situated at its base / The oil level in the sump or tank is normally checked after the engine has been stopped for a particular length of time. /


sun |noun| a very bright star around which the Earth revolves and which gives light and heat / The sun was just rising when we landed. The sun and the planets governed by the sun form the solar system. /


sunrise |noun| the time when the upper edge of the sun appears on the visible horizon. Abbreviation: SR


sunset |noun| the time when the upper edge of the sun just disappears over the horizon. Abbreviation: SS


super- |prefix| more than normal


supercharge |verb| to increase the power of an engine by using a supercharger / A supercharged engine delivers greater power than a non-supercharged engine of the same size. /


supercharger |noun| a blower or compressor, usually driven by the engine, for supplying air under high pressure to the cylinders of an internal combustion engine /The function of the supercharger is to increase the power output and maintain sea-level conditions at altitude./


super-cooled, supercooled |adjective| cooled below freezing point without solidification / Nimbo-stratus cloud is composed of liquid water droplets some of which are supercooled. /


superimpose |verb| to lay or to place something over the top of something else / The computer utilizes a technique in which each successive atmospheric layer is analyzed and superimposed on the previous ones. /


super-jet |noun| a large supersonic jet aircraft


supersonic |adjective| faster than the speed of sound / For sustained supersonic flight, tank insulation is necessary to reduce the effect of kinetic heating. /


supervisor |noun| a person in charge / senior cabin supervisor /


supplement |noun| an angle or arc that, when added to a given angle or arc, makes 180° or a semicircle - |verb| to add to in order to make more complete / The main power plant fire detection system should contain an audible warning device to supplement the visual indication. /


supplemental type certificate |noun| a certificate issued by an airworthiness authority to indicate that a modification to an aircraft or engine design has been approved. Abbreviation: STC


supplementary |adjective| extra or additional / supplementary information /


supplementary angle |noun| an angle that, when added to a given angle, makes 180°


supply |noun| the amount of something available for use / An engine requires an adequate supply of oil. / - |verb| to make available for use, to provide / A battery is designed to supply limited amounts of electrical power. / (NOTE: supplies – supplying – supplied)

supply line |noun| a hydraulic, fuel or pneumatic piping or electrical wiring which gives a source of energy

support |noun|  1. a device to hold something in position / Direct-reading indicators consist of a float contained within a metal support tube. /  2. practical assistance  3. providing information and services. In an unexpected situation caused by a technical failure, the crew will need additional information about alternate airports, weather conditions, runway surface conditions, priority landing, emergency services on the ground, airport facilities etc. - |verb| to bear the weight of / The wings support the aircraft in flight. /


support facilities |plural noun| equipment and buildings used by ground staff when working on aircraft at an airport


support services |plural noun| services provided to an aircraft while it is at an airport


suppress |verb|  1. to prevent the development or spreading of something - the fire crew suppressed the fire > the fire crew brought the fire under control  2. to prevent electrical interference from affecting a radio signal / R/T noise interference can be suppressed. /


suppressed antenna |noun| an antenna which is mounted under the airframe skin / Static interference can be reduced by installing suppressed antennas. /


suppression |noun|  1. the prevention of the development or spreading of something / a fire suppression system /  2. the prevention of electrical interference of a radio signal


suppressor |noun| a device used in an electrical or electronic system to reduce unwanted currents, e.g. a resistor or grid / A suppressor improves the quality of the signal. /


surface |noun|  1. an outer covering of something, or the top part of something / the surface of the wing /  2. the Earth’s surface or ground


surface air temperature |noun| the temperature recorded in the shade at a height just above ground level


surface front |noun| a weather front at the surface of the earth / The cirrus cloud can be 900 miles ahead of the surface front with a rain belt as wide as 200 miles. /


surface heating |noun| the heating of the ground by the sun


surface movement radar |noun| a type of radar used at airports to monitor aircraft traffic on the ground. Abbreviation: SMR


surface synoptic chart |noun| a chart of a geographical area with symbols, fronts and isobars giving a representation of the weather over the area at a particular time


surface tension |noun| the tension of the surface film of a liquid


surface wind |noun| a wind which blows across the land surface


surge |noun| a sudden increase in something such as electrical power - engine surge > instability in the power output of an engine - |verb| to move with force like a wave / If combustion pressure increases above compressor outlet pressure, the airflow will reverse in direction and surge forward through the compressor. /

surge margin |noun| the parameter that is the difference between the operating RPM and the RPM at which the compressor blades will stall at any altitude and for transient slam acceleration

surplus |adjective| excess, more than is needed / Fuel penalties can be incurred if fuel surplus to requirements is carried. /


surround |noun| something which encloses or borders / The design of windows, hatches or door surrounds is very critical. / - |verb| to encircle or to enclose / The Earth is surrounded by the atmosphere. /


surveillance |noun| the act of watching or monitoring

surveillance minimum altitude area |noun| a designated area in the vicinity of an aerodrome, in which the minimum safe levels allocated by a controller vectoring IFR flights with radar equipment have been predetermined

surveillance radar |noun| primary radar scanning, often through 360°

surveillance radar approach |noun| an approach guided by primary radar determining position, track and (with secondary surveillance radar) the identity of an aircraft

survey |noun| a detailed examination / An aerodrome meteorological office maintains a continuous survey of meteorological conditions over the aerodromes for which it is designated to prepare forecasts. / - |verb| to determine the boundaries, area, or elevations of land by means of measuring angles and distances / Take care when using wooded areas to fix position because the cutting down of trees may have led to a change in shape since the map was made. /


survival |noun| the fact of remaining alive after an accident / The survival of passengers in the sea depends on rapid location and rescue. /


survival beacon |noun| a beacon which transmits a signal which enables search aircraft to locate survivors in the water / VHF and/or UHF survival beacons are carried on all jet transports. /


survivor |noun| a person who continues to live after an accident / Whilst awaiting rescue on land or at sea, survivors should avoid exposure and conserve energy. The aircraft crashed into the sea and there were no survivors. /


susceptible |adjective| prone to, likely to be affected by / A rough surface is more susceptible to fatigue cracking than a smooth one, and for this reason highly stressed members are often polished. /


suspect |adjective| referring to something believed to be causing problems / The magnetic flaw detection technique is to induce a magnetic field in the suspect part and then to brush over it an ink containing a magnetic powder. / - |verb| to believe to be the case / If fuel contamination by water is suspected, a sample of fuel should be drained from the tank for inspection. /


suspend |verb|  1. to hang freely from a point / When it is freely suspended, a magnet will turn until one pole is towards the Earth’s magnetic north pole. /  2. to float freely in the air or in a liquid / The weather associated with visibility reductions by particles suspended in the atmosphere is classified as fog, mist, haze or smoke. /


suspension |noun|  1. the act of state of hanging freely from a point  2. the dispersion of particles in a liquid or gas / If a sample of fuel taken from a tank is hazy or cloudy in appearance, this indicates the presence of water in suspension. /


sustain |verb|  1. to continue, to maintain / For sustained supersonic flight, some measure of tank insulation is necessary to reduce the effect of kinetic heating. /  2. to receive, experience or suffer / The aircraft sustained major damage in the crash. The pilot sustained minor injuries. /


sweep |verb| to move across quickly and with force / Cold arctic air sweeps over North America in winter. /

sweeper |noun| a vehicle with rotary brush for removing dirt and debris

sweep-back |noun| an aircraft wing that slopes backwards towards the tail, forming an acute angle with the body of the aircraft


swell |noun| a long wave on water that moves continuously without breaking / When ditching an aircraft the selection of a landing direction which will result in the minimum relative speed between the aircraft and sea swell will reduce impact forces and minimize structural damage. /


sweptback |adjective| referring to a wing that slopes backwards towards the tail of the aircraft


swept-wing |adjective| referring to an aircraft that has sweptback wings


swing |verb|  1. to move from side to side with some force / There is often a tendency for a propeller driven aircraft to swing or yaw on take-off. /  2. - to swing a compass > to calibrate compass deviation by recording its value on a compass base while rotating the aircraft through 360°  3. - to swing a propeller > to turn a propeller by hand to start the engine


swirl |noun| a movement with a twisting motion / Swirls of smoke came out of the engine. /


swirl chamber |noun| a small chamber in the cylinder head to promote swirl / The usual method of atomizing the fuel is to pass it through a swirl chamber, so converting its pressure energy to kinetic energy. /


switch |noun| a device to open or break an electric current / There is an on/off switch on the front panel. / - centrifugal switch > a switch operated by centrifugal force - |verb| 1. to connect or disconnect two lines by activating a switch - to switch on > to start to provide power to a system by using a switch / Switch on the light. / - to switch off > to disconnect the power supply to a device or system / Switch off the navigation lights. / 2. to transfer, to move from one position or selection to another / Can you switch to the Tower frequency? /


symbol |noun| a printed or written sign used to represent something / The work done by an electrical circuit or the power consumed is measured in watts and is given the symbol P. /


symbolic |adjective| referring to symbols / A symbolic code is used for synoptic charts. /


symmetric, symmetrical |adjective| referring to something which has an exact likeness of form on opposite sides of a central dividing line / The area covered by the forecast is divided into a series of grid or reference points at approximately 300 km (kilometers) symmetrical spacing. /


symptom |noun| a sign or indication of something, possibly a problem / Buffet caused by turbulent airflow acting on the tailplane is one of the first symptoms of the approaching stall. /


synchronization |noun| occurrence at the same time or rate / Prior to engagement, when the aircraft is being flown manually, the autopilot system will be following the aircraft flight attitude, thus ensuring that synchronization is achieved. /


synchronize |verb| to cause to occur or operate at the same time or rate / The aircraft must be trimmed for the desired flight attitude before engaging the auto-pilot, which must be synchronized to maintain that attitude when it is engaged. /


synchronous |adjective| referring to something operating at the same time or rate / Synchronous motors will run at constant speed and are small and light in weight. /


synoptic |adjective| referring to something which gives a brief outline or general view of something more complex / With the addition of fronts and isobars, the synoptic chart provides a representation of the weather over a large area, at a particular time. /


synthetic |adjective| not natural, artificial / Mineral-based fluids are normally colored red, and must be used with synthetic rubber seals and hoses. /


system |noun| a group of interdependent parts forming and operating as a whole / a braking system, an electrical system / - System 1 > System 1 refers to the fact that nearly all systems are ‘duplexed’, i.e. there are two systems operating in parallel. In the case of instrumentation, System 1 usually provides the captain with information and System 2 the first officer.

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