Light Freezing Rain: Precipitation of liquid water particles which freezesuponimpact with theground or other
exposedobjects, either in the form of drops of more than0.5mm (0.02 inch) or smallerdrops which, in contrast to
drizzle,are widely separated. Measured intensity ofliquidwater particles is up to 2.5mm/hour (0.10 inch/hour) or 25
grams/dm2/hourwith a maximum of 0.25 mm (0.01 inch) in6minutes.
Light Icing: Therate of accumulation may create a problem if flightisprolonged in thisenvironment (over 1 hour).
Occasionaluse of deicing/anti-icingequipmentremoves/prevents accumulation.
Liquid Water Content (LWC): The total mass of water contained in all the liquidclouddroplets withina unit volume of
cloud.Units of LWC are usually grams of water per cubicmeterof air (g/m3).
Low (Pressure System): An area of low pressure completely surrounded byhigherpressure.
Low-level Wind Shear: Wind shear that occurs within 2000 feet of the surface.
Lowest Operational UseTemperature(LOUT): For a givenfluidis the higher of the lowesttemperature at which the
fluidmeets the aerodynamic acceptance test for agivenaircraft type, or the actualfreezing point of the fluid plus a
freezingpoint buffer of 7°C for type I or 10°C for typeIIIII & IV.
Mean Sea Level (MSL) Altitude: Altitude expressed in feet measured from meansea level.
Maneuvering Area: That part of an aerodrome to be used for thetake-off,landing and taxiingof aircraft, excluding
aprons.
Median Volumetric Diameter (MVD): The droplet diameter that divides the totalamount of waterinhalf; half the water
volumewill be in larger droplets and half insmallerdroplets.
Micron: One-millionthof a meter or one-thousandth of a millimeter.
Minimum En Route IFR Altitude (MEA): The lowest published altitude between radiofixes thatassuresacceptable
navigationalsignal coverage and meets obstacleclearancerequirements between those fixes.The MEA prescribed
fora Federal airway or segment thereof, area navigationlowor high route, orother direct route applies to the entire
widthof the airway, segment, or route between the radiofixesdefining the airway,segment, or route.
Minimums: Minimumweather condition requirements established foraparticular operation or typeof operation (e.g.,
IFRtakeoff or landing, alternate airport for IFR flightplans,VFR flight, etc.).
Missed Approach: A maneuver conducted by a pilot when an instrumentapproachcannot becompleted to a landing.
Theroute of flight and altitude are shown oninstrumentapproach procedure charts.A pilot executing a missed
approachprior to the Missed Approach Point (MAP)mustcontinue along the final approachto the MAP. The pilot may
climbimmediately to the altitude specified in themissedapproach procedure. Atlocations where ATC radar service is
provided,the pilot should conform to radar vectorswhenprovided by ATC in lieu of thepublished missed approach
procedure.
Mixed Ice: Theice type that appears clear near the stagnationlineturning to white rime nearthe edges. It occurs at
conditionsbetween those that form pure clear and pure rimeice.Similar to clear ice, mixedice accretions can
significantlydisrupt airflow and cause handlingandperformance problems.
Mixed Icing Conditions: An atmospheric environment where supercooled liquid waterandice crystalscoexist.
Moderate and Heavy Freezing Rain: Precipitation of liquid water particles whichfreezesuponimpact with the ground
orother exposed objects, either in the form of drops ofmorethan 0.5 mm (0.02inch) or smaller drops which, in contrast
todrizzle, are widely separated. Measured intensity ofliquidwater particles ismore than 2.5 mm/hour (0.10 inch/hour)
or25 grams/dm2/hour.
Moderate Icing: The rate of accumulation is such that even shortencountersbecomepotentially hazardous and use of
deicing/anti-icingequipment or flight diversion is necessary.
Notice to Airmen (NOTAM): A notice containing information (not known sufficientlyinadvance topublicize by other
means)concerning the establishment, condition, or changeinany component (facility,service, or procedure of, or
hazardin the National Airspace System) the timelyknowledgeof which is essential topersonnel concerned with flight
operations.
Obstacle: Anexisting object, object of natural growth, or terrain atafixed geographicallocation or which may be
expectedat a fixed location within a prescribed areawithreference to which verticalclearance is or must be provided
duringflight operation.
Occluded Front: Occur when an air mass is trapped between two colderairmasses and isforced to higher altitudes.
Occludedfronts may combine characteristics of both warmandcold fronts.
Orographic: Theair temperature indicated by the aircraft'stemperatureprobe. Depending uponthe temperature probe
design,Outside Air Temperature (OAT) will be somewhere intherange between the StaticAir Temperature (SAT) and
theTotal Air Temperature (TAT). Flight computers maycorrectOAT to read eitherSAT or TAT. (see also Static Air
Temperatureand Total Air Temperature).
Outside Air Temperature (OAT): The air temperature indicated by theaircraft'stemperatureprobe. Depending upon
thetemperature probe design, Outside Air Temperature(OAT)will be somewhere inthe range between the Static Air
Temperature(SAT) and the Total Air Temperature (TAT).Flightcomputers may correct OAT toread either SAT or TAT.
(seealso Static Air Temperature and Total Air Temperature).
Pilot Briefing: A service provided by the FSS to assist pilots inflightplanning.Briefing items may include weather
information,NOTAMS, military activities, flowcontrolinformation, and other items asrequested.
Pilot-in-Command (PIC): The pilot responsible for the operation and safety ofanaircraft duringflight time.
Pilot Briefing: A service provided by an FSS to assist pilots withflightplanning.Briefing items may include weather
information,notices to airmen (NOTAMs), militaryactivities,flow control information, andother items, as requested.
Pilot's Discretion: A service provided by an FSS to assist pilots withflightplanning.Briefing items may include
weatherinformation, notices to airmen (NOTAMs), militaryactivities,flow controlinformation, and other items, as
requested.
Pilot Report (PIREP): A report of meteorological phenomena encountered byaircraftin flight.
Precipitation: Therate at which precipitation is either measure or judgetobe falling. Winterprecipitation is a key factor
inestimating the Holdover Time for an anti-icing fluid. Itisthe indication ofmoisture content.
Precipitation Rate: Any or all of the forms of water particles, whether liquidorsolid, thatfall from the atmosphere and
reachthe ground.
Pre-Takeoff Check: A check, after deicing application, to ensure allaircraftsurfaces arefree of frozen contaminants.
Pre-Takeoff Contamination Inspection: An inspection conducted by a qualifiedperson,immediatelyprior to take-off,
todetermine if an aircraft's critical surfacesarecontaminated by frost, ice,slush or snow. This inspection is mandatory
undersome circumstances.
Pre-Takeoff ContaminationInspectionReport: This reportmustbe made to thepilot-in-command and, when a
documentedinspection method has not been used, mustdescribehow the inspection wasconducted. The report must
alsoconfirm that all critical surfaces are freeofcontamination.
Relative Humidity: The ratio, expressed as a percentage, of water vaporpresentcompared withthe maximum amount
possibleat the present temperature.
Representative Surface: Surfaces which can be readily and clearly observed byflightcrew duringday and night
operations,and which are suitable for judging whether ornotcritical surfaces arecontaminated. Examination of one or
morerepresentative aircraft surfaces may be used forthePre-Take-off ContaminationInspection, if a tactile
examinationis not required. Transport Canada must approvetheuse of these aircraftspecific surfaces.
Residual Ice: Icethat remains on the boot immediately after abootinflation and deflation.
Rime Ice: Theice type that appears rough, milky and opaque. Rime iceisformed by theinstantaneous freezing of
supercooleddroplets as they strike the aircraft.
Runback: Icingthat occurs when liquid water impacts an aircraftsurface,flows aft past theimpact region, and then
freezes.This can occur at near freezing temperatures,withvery high liquid waterlevels, or when a thermal ice
protectionsystem doesn't evaporate the impacting water.
Sectional Aeronautical Charts: (1:500,000) Designed for visual navigation ofslow ormediumspeed aircraft.
Topographicinformation on these charts features theportrayalof relief and a judiciousselection of visual checkpoints
forVFR flight. Aeronautical information includes visualandradio aids tonavigation, airports, controlled airspace,
restrictedareas, obstructions, and related data.
Service Provider: The organization providing de/anti-icing related servicestoair operatorsat a given location. The
ServiceProvider may be a qualified third party,anotherairline, or the Air Operator.The Service Provider must provide
a servicein accordance with the air operator’sapprovedground icing program, where sucha program exists.
Severe Icing: Therate of accumulation is such thatdeicing/anti-icingequipment fails to reduceor control the hazard.
Immediateflight diversion is necessary.
SIGMET: ASIGnificant METeorological advisory that warns ofphenomenathat affect allaircraft. SIGMET advisories
coversevere and extreme turbulence, severe icing,andwidespread dust or sandstormsthat reduce visibility to less
than3 miles.
Slush: Snowthat has a water content exceeding its freelydrainedcondition such that ittakes on fluid properties (e.g.,
flowingand splashing).
Snow: Aporous, permeable aggregate of ice grains that canbepredominantly singlecrystals or close groupings of
severalcrystals.
Snow Grains: Precipitationthat comprises very small white andopaquegrains of ice. These grains arefairly flat or
elongated;their diameter is less than 1 mm. When theyhithard ground, they do not bounceor shatter.
Snow Pellets: Precipitationwhich consists of white and opaque grainsofice. These grains are spherical orsometimes
conical;their diameter is about 2-5 mm. Grains arebrittle,easily crushed. They dobounce and break on hard ground.
Stabilator: Atail surface that acts as both stabilizer andcontrolsurface. The moveablesurface can minimize the local
angleof attack, so this form of tail surface is consideredtobe less susceptible totail stall than a standard horizontal
stabilizer.
Stability: Theproperty of an air mass to resist verticaldisplacementfrom its initialposition. If an air mass is stable, then
anoutside force is required to raise it for cloudformation.On the other hand,unstable air is buoyant and can rise to
initiatecloud formation.
Staging Bay: A dedicatedarea behind and adjacent to each deicingbay,where aircraft await approval toenter the
deicingbay.
Standard Terminal Arrival(STAR)Charts: Designedtoexpedite air traffic controlarrival procedures and to facilitate
transitionbetween en route and instrumentapproachoperations. Each STAR procedure ispresented as a separate
chartand may serve a single airport or more than oneairportin a given geographicallocation.
Static Air Temperature (SAT): The ambient temperature of air. Static AirTemperature(SAT)is measured with little or
noair motion past the temperature probe. This is theairtemperature thatcommonly appears in weather forecasts and
reports.SAT aloft is typically measured by balloon (SeealsoOutside Air Temperatureand Total Air Temperature).
Stratiform or Stratus Couds: Clouds of extensive horizontal development and a stableairmass.
Sublimation: Aprocess where ice turns directly into water vaporwithoutpassing through aliquid state.
Supercooled: Waterthat remains in the liquid state eventhoughtemperatures are below 0°C. Clouddroplets can exist
as aliquid at temperatures down to about -40°C.
Supercooled Large Droplets (SLD): Supercooled cloud droplets, freezing drizzle,or freezingrainwith a Mean
VolumetricDiameter greater than 50 microns. Due totheirrelatively large size and highmass, SLD are particularly
hazardousto aircraft since they can impact theaircraftsurfaces outside the iceprotected regions.
Supercooled Liquid Water (SLW): Liquid water at temperatures below 0°C. SLW isfoundinclouds, freezing drizzle,
andfreezing rain in the atmosphere. This water freezesonaircraft surfaces. Mostaircraft icing occurs in supercooled
clouds,which consist of SLW, sometimes with ice crystals.
Supermental Weather Service Location: An airport facility staffed with contractpersonnel whotakeweather
observationsand provide current local weather to pilotsviatelephone or radio.
Tactile Inspection: An inspection requiring a person to physicallycontactspecific aircraftsurfaces. Tactile inspections,
undercertain circumstances, may be the only way ofconfirmingthat the criticalsurfaces of an aircraft are not
contaminated.For some aircraft, tactile inspectionsaremandatory, as part of thedeicing/anti-icing inspection process,
toensure that the critical surfaces are free offrozencontaminants.
Taxiway: Adefined path on a land aerodrome established for thetaxiingof aircraft andintended to provide a link
betweenone part of the aerodrome and another.
Temperature Inversion: Atmospheric condition where temperature increaseswithaltitude.
Terminal Deicing Facility: A deicing facility for one or several aircraft located atornear theterminal or other location
whereaircraft loading activity normally takes place.
Terminal Area: Ageneral term used to describe airspace in whichapproachcontrol service orairport traffic control
serviceis provided.
Total Air Temperature (TAT): Kinetic heating causes the Total (or Ram) AirTemperature(TAT) to bewarmer than the
StaticAir Temperature (SAT). For example, if the SAT is-2C,an aircraft traveling at250 knots would observe a TAT of
approximately+5C. TAT is close to the temperature of thewingleading edge, which alsoexperiences ram rise (see
alsoStatic Air Temperature and Outside Air Temperature).
Tower: Aterminal facility that uses air/groundcommunications,visual signaling, andother devices to provide ATC
servicesto aircraft operating in the vicinity of anairportor on the movement area.Authorizes aircraft to land or takeoff
atthe airport controlled by the tower or to transit theClassD airspace arearegardless of flight plan or weather
conditions(IFR or VFR). A tower may also provideapproachcontrol services (radar ornonradar).
Trace Icing: Icebecomes perceptible. Rate of accumulation isslightlygreater than the rate ofsublimation. Deicing/
anti-icingequipment is not utilized unless encountered foranextended period of time(over 1 hour).
Trimmable Stabilizer: A horizontal stabilizer that can be pitched to trimtheelevator. Thissurface movement can
minimizethe local angle of attack, so this form oftailsurface is considered to beless susceptible to tail stall than a
standardhorizontal stabilizer.
True Airspeed: Theairspeed of an aircraft relative to undisturbed air.Usedprimarily in flightplanning and en route
portionof flight. When used inpilot/controllercommunications, it is referred to as"true airspeed"and not shortenedto
"airspeed."
Turbojet Aircraft: An aircraft in which thrust is produced entirely by theforceof the airexpelled by the engine. The
engine'smain components are an inlet, a compressor,acombustion chamber, a turbine,and a nozzle. The turbine
drivesthe compressor.
Turboprop Aircraft: An aircraft in which thrust is produced primarily byapropeller. Theengine's main components are
aninlet, a compressor, a combustion chamber, a turbine, andanozzle. Typicallythere is a split turbine that drives both
thecompressor and the propeller.
Urgency: Acondition of being concerned about safety and ofrequiringtimely but notimmediate assistance; a
potentialdistress condition.
Vector: Aheading issued to an aircraft to providenavigationalguidance by radar.
VFR Terminal Area Charts: (1:250,000) Depict Class B airspace which provides forthecontrol orsegregation of all
theaircraft within Class B airspace. The chart depictstopographicinformation andaeronautical information that
includesvisual and radio aids to navigation,airports,controlled airspace, restrictedareas, obstructions, and related
data.
Visibility: Theability, as determined by atmospheric conditions andexpressedin units ofdistance, to see and identify
prominentunlighted objects by day and prominentlightedobjects by night. Visibility isreported as statute miles,
hundredsof feet or meters.
Visible Moisture: Moisture in the form of clouds or precipitation.
Visual Flight Rules (VFR): FARs that govern flight in visualmeteorologicalconditions-flight byreference to the natural
horizonand surface.
Visual Flight Rules (VFR)Conditions: Weatherconditions equal to or better than theminimum forflight under visual
flightrules. The term may be used as anATCclearance/instruction only when: an IFRaircraft requests a climb/descent
inVFR conditions, the clearance will result innoiseabatement benefits wherepart of the IFR departure route does not
conformto an FAA approved noise abatement route oraltitude,or a pilot has requesteda practice instrument
approachand is not on an IFR flight plan.
VOR: Aground-based electronic navigation aid transmittingveryhigh frequencynavigation signals, 360 degrees in
azimuth,oriented from magnetic north. Used as the basisfornavigation in the NationalAirspace System. The VOR
periodicallyidentifies itself by Morse Code and may haveanadditional voice identificationfeature. Voice features may
beused by ATC or FSS for transmittinginstructions/informationto pilots.
Water Vapor: Thegas phase of water.
Water Spray Endurance Test(WSET): A laboratory testthat measures the endurancetime ofanti-icing fluids under
conditionsof light freezing precipitation. This test isusedto classify and to certifyfluids according to SAE AMS
specifications.
Wind Shear: Anyrapid, horizontal, or vertical change in wind directionorspeed.
World Aeronautical Charts (WAC): (1:1,000,000) Provide a standard series ofaeronauticalchartscovering land areas of the world at a size and scale convenientfornavigation by moderate speedaircraft. Topographic information includescities and towns, principal roads, railroads,distinctive landmarks,drainage,and relief. Aeronautical information includes visual and radio aidsto navigation,airports, airways, restrictedareas, obstructions, andother pertinent data.
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