MODULE 2

AVIATION METEOROLOGY

WE WILL DISCUSS THE FOLLOWING SUBJECTS IN THIS MODULE, WHICH WILL INCLUDE THEORY AND COMPANY OPERATIONAL PROCEDURES.

• PROPERTIES OF THE ATMOSPHERE.

• THE INTERNATIONAL STANDARD ATMOSPHERE (ISA).

• SNOW AND ICE.

• DE-ICING AND ANTI-ICING PROCEDURES.

• VISIBILITY AND RUNWAY VISUAL RANGE (RVR).

• AVIATION WEATHER, METAR, TAF AND SNOWTAM.

• ADVERSE WEATHER CONDITIONS IN THE MIDDLE EAST AND ASIA.

PROPERTIES OF THE ATMOSPHERE.

• AS WE OBVIOUSLY KNOW THE ATMOSPHERE IS MADE UP OF AIR!

• BUT AIR HAS BOTH MASS AND PRESSURE.

• THE ATMOSPHERE IS AN ENVELOPE OF GASES WHICH SUROUNDS THE EARTH.

• ABOUT 78% OF THE AIR IS MADE UP OF NITROGEN, ABOUT 20% IS OXYGEN AND 0.04% IS CARBON DIOXIDE.

• THE TROPOSPHERE IS THE LOWEST LAYER OF THE ATMOSPHERE AND SEPERATED FROM THE UPPER LEVELS BY THE TROPOPAUSE. MOST OF THE WEATHER WHICH AFFECTS US IN AVIATION CAN BE CONSIDERED TO BE IN THE TROPOSPHERE, AS MOST OF THE AIR AND WATER VAPOUR IN THE ATMOSPHERE IS LOCATED HERE.

• THE TROPOSPHERE EXTENDS UP TO 5-8 MILES HIGH. AND IN THIS LAYER TEMPERATURE DECREASES WITH HEIGHT.

PRESSURE.

Atmospheric pressure is the force exerted by air on a unit area. It can be thought of simply as the weight of the air above a given point. Simply, the fewer molecules above you, the lower the pressure exerted on you and vice versa (more molecules above = higher pressure). Since there are fewer molecules above you as you move up in the atmosphere, pressure always decreases with increasing altitude.

TEMPERATURE.

• The layer closest to the earth's surface is the troposphere and it is a very important layer to meteorologists because it is the layer that contains all of our weather.

• Sunlight warms the earth's surface and then the surface warms the air above it. As one moves away from the earth's surface (the heat source), the air becomes cooler. This is why temperature usually decreases with height in the troposphere.

• Sometimes the air temperature may increase with height in a narrow layer. This is referred to as a temperature inversion. Air temperature may also stay the same with increasing height. This is called an isothermal layer.

• At about the altitude where jet aircraft fly (~30,000 ft), the air temperature becomes isothermal.

• The bottom of this isothermal layer marks the end of the troposphere and the beginning of the stratosphere. The boundary separating the troposphere from the stratosphere is called the tropopause.

Dew-point Temperature.

• Dew-point temperature is a measure of the moisture content in the atmosphere and is the temperature to which air must be cooled (at constant pressure, with no change in water vapour content) for saturation to occur.

• When saturation is reached, condensation occurs and such things as dew, frost or fog may occur. The dew-point temperature is a good indicator of the actual amount of water vapour in the air. This is obviously of importance to us in aviation as we need to understand when fog can occur as this phenomenon can have a large impact on our operation.

• High dew-point temperatures indicate there is high water vapour content, which indicates the air is moist. Low dew-point temperatures indicate there is low water vapour content, which indicates the air is dry.

• So when the actual outside temperature and the calculated dew-point temperature are the same, then fog can occur………Then our operation could be affected by restrictions delays and in the worst case…..cancellations of flights.

The Water Cycle.

The water cycle refers to the continuous movement of water between the earth and the atmosphere.

Evaporation.

Evaporation is the process by which a substance changes from the liquid phase to the gas phase. On earth, the most important substance is water (liquid water into water vapour).

Energy is required for evaporation to occur. Energy can come from the sun (radiation), the atmosphere (conduction) or the earth (conduction).

When energy is extracted from the atmosphere to evaporate liquid water, the atmosphere will cool. This is also true if water evaporates off a surface.

Evaporation is very important because it is how water vapour, which is needed for clouds and precipitation, enters the atmosphere.

Condensation.

Condensation is the process by which a substance changes from the gas phase to the liquid phase.

As air containing water vapour rises into the atmosphere, it will expand and cool. If it cools to its dew-point temperature, the air will become saturated and condensation will occur.

Condensation can be observed in the atmosphere as clouds, fog, dew, or frost form.

When condensation occurs, the heat required to originally evaporate the water is returned to the atmosphere, causing the atmosphere to warm.

Precipitation.

Clouds are composed of millions of water droplets that have condensed.

These water droplets grow into larger droplets by colliding and joining with one another. Eventually, the droplets can grow large enough that they will not be able to stay suspended in the cloud.

When this occurs, they fall out of the cloud as precipitation.

If the cloud's temperature is below freezing, it will contain ice crystals.

Ice crystals collide and stick to other ice crystals and eventually fall from the cloud as snow.

Precipitation is water, either liquid or solid, that falls from the atmosphere to the surface.

CLOUD TYPES.

STRATIFORM, COMMONLY KNOWN AS STRATUS CLOUDS.

CUMULIFORM, COMMONLY KNOWN AS CUMULUS AND CUMULONIMBUS CLOUDS.

Wind.

Wind is simply air in motion relative to the earth's surface.

We normally think of the wind as the horizontal motion of the air, although air actually moves in three dimensions.

The vertical component of the wind is generally quite small, except in thunderstorm updrafts. The vertical motion of air, however, is very important in determining our weather.

Air that is rising cools, which may cause it to reach saturation and form clouds and precipitation.

Conversely, air that is sinking warms, which causes clouds to evaporate and produce clear weather.

Surface maps usually have H's and L's at various locations.

The H's and L's represent high and low pressure systems.

On weather maps highs and lows are surrounded by lines called isobars.

Isobars are lines of constant pressure; they connect every location that has the same value of pressure.

When isobars are packed close together, the pressure is changing rapidly over a small distance. The closer the isobars are packed together, the stronger the wind.

In the Northern Hemisphere the wind blows clockwise around a high pressure system.

Around a low pressure system, the wind blows counter-clockwise.

For our purposes we don’t need to know why…..just accept that this is how the air circulates!

Air Masses.

An air mass is a large body of air that has relatively uniform temperature and humidity characteristics.

The regions where air masses form are referred to as air mass source regions.

If air remains over a source region long enough, it will acquire the properties of the surface below.

Ideal source regions are regions that are generally flat and of uniform composition.

Examples include central Canada, Siberia, the northern and southern oceans and large deserts.

Air masses are classified according to their temperature and moisture characteristics.

They are grouped into four categories based on their source region.

Air masses that originate in the cold, polar regions are designated with a capital "P" for polar.

Air masses that originate in the warm, tropical regions are designated with a capital "T" for tropical.

Air masses that originate over land will be dry and are designated with a lowercase "c" for continental.

Air masses that originate over water will be moist and are designated with a lowercase "m" for maritime. These letters are combined to indicate the type of air mass:

cP: cold, dry air massmP: cold, moist air masscT: warm, dry air massmT: warm, moist air mass

In winter, one more type of air mass may form, an extremely cold, dry air mass referred to as cA, continental arctic.

Once formed, air masses can move out of their source regions bringing cold, warm, wet, or dry conditions to other parts of the world.

FRONTS.

A ‘front’ is simply the boundary between two air masses.

Front’s are classified by which type of ‘air mass’ (cold or warm) is replacing the other.

COLD FRONTS.

A front is called a cold front if the cold air mass is replacing the warm air mass.

The air behind a cold front is colder and typically drier than the air ahead of it, which is generally warm and moist.

There is typically a shift in wind direction as the front passes, along with a change in pressure tendency (pressure falls prior to the front arriving and rises after it passes).

Cold fronts have a steep slope, which causes air to be forced upward along its leading edge. This is why there is sometimes a band of showers and/or thunderstorms that line up along the leading edge of the cold front.

Cold fronts are represented on a weather map by a solid blue line with triangles pointing in the direction of its movement.

WARM FRONTS.

A warm front occurs when a cold air mass is receding (i.e. a warm air mass is replacing a cold air mass).

The air behind a warm front is warm and moist, while the air ahead of a warm front is cooler and less moist.

Similar to the cold front, there will a shift in wind direction as the front passes and a change in pressure tendency.

Warm fronts have a more gentle slope than cold fronts, which often leads to a gradual rise of air. This gradual rise of air favours the development of widespread, continuous precipitation, which often occurs along and ahead of the front.

Warm fronts are represented on a weather map by a solid red line with semi-circles pointing in the direction of its movement.

OCCLUDED FRONTS.

Generally, cold fronts move faster than warm fronts, however, sometimes in a storm system the cold front will "catch up" to the warm front.

An occluded front forms as the cold air behind the cold front meets the cold air ahead of the warm front.

Which ever air mass is the coldest undercuts the other.

The boundary between the two cold air masses is called an occluded front.

Occluded fronts are represented on weather maps by a solid purple line with alternating triangles and semi-circles, pointing in the direction of its movement.

FRONTAL SYSTEMS ARE DEPICTED ON LOW LEVEL SIGNIFICANT WEATHER CHARTS.

THUNDERSTORMS.

Generally thunderstorms are known by their cloud classification name, Cumulo Nimbus or CB.

These clouds are of a similar degree of importance as the phenomenon of fog.

Aircraft should never fly through a thunderstorm due to the very fast up and down currents of air. These currents of air can destabilise an aircraft, the hail inside the cloud can damage the fuselage or shatter windows.

Thunderstorms in the vicinity can cause a phenomenon called windshear, which is technically, a rapidly changing wind direction in a short distance.

Aircraft have crashed as a result of thunderstorms or been severely damaged. This is why this cloud type above all others needs to be respected.

WINDS BOTH ALOFT (I.E. AIRBORNE) AND ON THE GROUND (I.E. FOR TAKE-OFF AND LANDING).

WE WILL CONSIDER THE WINDS WHICH AFFECT OUR AIRCRAFT WHEN AIRBORNE, SUCH AS JETSTREAMS. WHAT THEY ARE AND HOW THEY AFFECT OUR AIRCRAFT, AS WELL AS HOW THE INFORMATION IS PRODUCED FOR THE PILOTS.

WE WILL ALSO CONSIDER THE WINDS ON THE GROUND AND HOW THE INFORMATION ID HANDED TO THE PILOTS ONCE AGAIN.

BASICALLY:THE WINDS ALOFT CAN BE THOUGHT OF AS BEING WINDS WHICH FLOW TO……..THE WINDS ON THE GROUND AS BEING WINDS WHICH FLOW FROM…….

LATER IN THIS MODULE WE WILL GO INTO FURTHER DETAIL ON THE ACTUAL REPORTS WHICH ARE PRODUCED FOR THE PILOTS.

WIND INFORMATION IS ENCLOSED IN REPORTS CALLED METARS, TAFS, WIND CHARTS AND SIGNIFICANT WEATHER CHARTS.COPIES OF WHICH ARE INCLUDED IN YOUR HANDOUTS.

UPPER WINDS.

WE WILL CONCENTRATE INITIALLY ONLY ON THE EARTH’S NORTHERN HEMISPHERE, AS THIS IS THE REGION WHICH WE PREDOMINANTLY OPERATE IN.

AS WE DISCUSSED EARLIER THE WINDS FLOW IN A CLOCKWISE DIRECTION AROUND A HIGH PRESSURE AREA AND ANTI (OR COUNTER) CLOCKWISE DIRECTION AROUND A LOW PRESSURE AREA.

THE STRONGEST WINDS ARE CALLED JETSTREAMS AND THEY CAN BE COMPARED TO FAST RUNNING ‘RIVERS’ OF AIR IN THE UPPER ATMOSPHERE.

PILOT’S ARE INTERESTED IN JETSTREAMS STRENGTH AND DIRECTION, AS THEY CAN BE AS STRONG AS 200 KNOTS IN THE MOST EXTREME CIRCUMSTANCES, WHICH CAN PROVIDE EITHER VERY STRONG HEADWINDS OR TAILWINDS, WHICH WILL AFFECT THE LENGTH OF TIME IT WILL TAKE TO FLY THROUGH THESE AREAS, SO AFFECTING THE AMOUNT OF FUEL USED.

BECAUSE OF THE STRENGTH OF THESE JETSTREAMS THEY CAN CAUSE CLEAR AIR TURBULENCE (C.A.T.) ESPECIALLY WHEN CROSSING THESE AREAS AT 90 DEGREES, DUE TO THE LARGE SHIFT IN WIND DIRECTION AND THE RAPID INCREASE IN THE WIND’S STRENGTH.

JETSTREAMS ARE DEPICTED ON HIGH LEVEL SIGNIFICANT WEATHER CHARTS.

HIGH LEVEL SIGNIFICANT WEATHER CHART.

JETSTREAMS.

CLEAR AIR TURBULENCE (C.A.T.)

Ofp shere values

MOUNTAIN WAVES.

MOUNTAIN WAVES AND LENTICULAR CLOUDS.

UPPER LEVEL WINDS

UPPER LEVEL WINDS, NOT INCLUDING JETSTREAMS, ARE ONCE AGAIN OF AN INTEREST TO PILOTS, AS OVER THE COURSE OF A FLIGHT THEY WILL DETERMINE THE LENGTH OF TIME WHICH THE FLIGHT TAKES AND THEREFORE THE AMOUNT OF FUEL REQUIRED TO TRAVEL THIS ROUTE.

ON THE PILOT’S COMPUTER GENERATED OPERATIONAL FLIGHT PLAN (O.F.P.) A WIND IS GIVEN FOR EACH SECTOR BETWEEN WAYPOINTS, OF INTEREST TO THE PILOTS AS THEY ENTER THESE WINDS INTO THEIR FLIGHT MANAGEMENT COMPUTERS TO ASSIST INFLIGHT FUEL AND TIME PREDICTIONS AS WELL AS VERTICAL NAVIGATION, I.E. CLIMBS AND DESCENTS.

ALSO ON THE O.F.P. THERE IS AN AVERAGE WIND COMPONENT COMPUTED FOR THE ENTIRE ROUTE FROM DEPARTURE TO DESTINATION. THIS IS OF USE TO THE PILOTS AS THEY HAVE A QUICK CHECK THAT THE INFORMATION GENERATED BY THE COMPUTER IS THE SAME AS THAT DEPICTED ON THEIR OWN UPPER WIND AND TEMPERATURE CHART.

UPPER LEVEL WIND AND TEMPERATURE CHART.

OUTSIDE AIR TEMPERATURE WHEN AIRBORNE.

AGAIN THIS INFORMATION IS DEPICTED BOTH ON THE O.F.P. FOR EACH SECTOR BETWEEN WAYPOINTS AND ALSO ON THE UPPER WIND AND TEMPERATURE CHARTS.

THESE CHARTS ARE PRODUCED FOR DIFFERENT FLIGHT LEVELS WHICH THE AIRCRAFT COULD BE PLANNED TO FLY AT.FOR EXAMPLE, FL300 (30,000 FEET), FL340 (34,000 FEET) AND SO ON.

THE OUTSIDE AIR TEMPERATURE IS IMPORTANT FOR THE FOLLOWING REASONS:

• A RAPID CHANGE IN TEMPERATURE CAN BE AN INDICATION OF CLEAR AIR TURBULENCE.

• IT IS LESS ECONOMICAL TO FLY AT LEVELS WITH HIGH TEMPERATURES AS THE AIRCRAFTS ENGINES REQUIRE MORE POWER, AS THE AIR IS THINNER, WHICH IN TURN USES MORE FUEL.

• LOW TEMPERATURES OVER THE DURATION OF A LONG FLIGHT CAN CAUSE THE FUEL TO COOL TO IT’S FREEZE POINT….WHICH IS A TERM USED TO DESCRIBE THE FUEL TURNING ‘WAXY’….THIS CAN CAUSE AN ENGINE TO FLAME-OUT, I.E. SHUT DOWN AS IT BECOMES STARVED OF FUEL.

BOEING PRODUCES PERFORMANCE CHARTS FOR FLIGHT IN THE CRUISE, BASED ON THE INTERNATIONAL STANDARD ATMOSPHERE. PILOTS CAN THEREFORE USE THE TEMPERATURE DEPICTED ON THESE CHARTS AND CONVERT IT TO ITS I.S.A. VALUE. A VALUABLE TOOL FOR VARIOUS INFLIGHT SITUATIONS.

BOEING 747-400 LONG RANGE CRUISE TABLE.

BOEING 747-400 ONE ENGINE INOPERATIVE TABLE.

WIND EFFECT ON TAKE-OFF AND LANDING.

DUE TO THE PHYSICS OF THE ATMOSPHERE (KNOWN IN THIS CASE AS THE GEOSTROPHIC EFFECT) WINDS TEND TO VEER (MOVE IN A CLOCKWISE DIRECTION) AND INCREASE IN STRENGTH AS HEIGHT ABOVE THE GROUND INCREASES.

GROUND ‘BASED’ WINDS CAN ALSO BE AFFECTED BY OBSTACLES, SUCH AS HANGARS AND OTHER LARGE BUILDINGS IN THE VICINITY OF AIRPORTS. AS WELL AS THE LOCAL ‘TOPOGRAPHY’, WHICH MEANS….HILLS AND MOUNTAINS.

IF THE AIRPORT IS LOCATED ON THE COASTLINE, I.E. BY THE SEA, THEN BOTH SEA AND LAND BREEZES WILL AFFECT THE WIND DIRECTION ALSO.WITH A SEA BREEZE DURING THE DAY, FLOWING FROM THE SEA TO INLAND, PRIMARILY DUE TO THE LAND HEATING UP FASTER THAN THE WATER FROM THE SUN’S POWER.CONVERSELY, A LAND BREEZE WILL FLOW FROM THE LAND TO OFFSHORE, DUE TO THE LAND COOLING FASTER THAN THE WATER BECAUSE OF HEAT RADIATING INTO THE ATMOSPHERE.

‘TOPOGRAPHIC’ WINDS ARE OFTEN DESCRIBED AS EITHER KATABATIC OR ANABATIC AND WE WILL LOOK AT THESE SHORTLY.

SEA BREEZE.

LAND BREEZE.

KATABATIC WINDS.

ANABATIC WINDS.

NOW THAT WE KNOW WHERE THE WIND IS COMING FROM, THEN THIS INFORMATION CAN BE PASSED ON TO THE PILOTS.

EITHER AS AN ACTUAL WEATHER REPORT OR A FORECAST. IN THESE REPORTS THE WINDS ARE REFRENCED TO TRUE NORTH.

AT AIRPORTS OF DEPARTURE AND ARRIVAL AN A.T.I.S. (AIRPORT TRAFFIC INFORMATION SERVICE) THE WIND DIRECTION IS REFERENCED TO MAGNETIC NORTH, AS A QUICK COMPARISON THEN TO THE RUNWAY’S ORIENTATION TO MAGNETIC NORTH.

MORE ON THESE ACTUAL TYPES OF REPORTING SYSTEMS LATER IN THIS MODULE.

THESE WINDS IN THE VICINITY OF AIRPORTS CAN HAVE LARGE EFFECTS ON THE AIRCRAFT’S PERFORMANCE:

• HEADWINDS ARE THE MOST BENEFICIAL TO PILOTS AS THEY REDUCE THE AIRCRAFT’S GROUNDSPEED ON APPROACH AND THEREFORE THE LENGTH OF RUNWAY REQUIRED TO LAND ON. HOWEVER STRONG HEADWINDS CAN AFFECT THE CAPABILITIES OF THE AUTOPILOT SYSTEMS AND PREVENT THE PILOTS FROM CARRYING OUT AN AUTOMATIC LANDING. FOR THE BOEING 747-400 THIS IS A HEADWIND COMPONENT OF 25 KNOTS.

• ON TAKE-OFF A HEADWIND IS AGAIN BENEFICIAL TO THE PILOT AS IT REDUCES THE LENGTH OF RUNWAY REQUIRED TO BECOME AIRBORNE. THEREFORE EITHER ALLOWING THE AIRCRAFT TO DEPART WITH A LARGER PAYLOAD…….GOOD FOR THE COMPANY…..OR USE A LOWER ENGINE POWER SETTING, AGAIN GOOD FOR THE COMPANY AS IT REDUCES THE STRESS ON THE ENGINE AND THEREFORE REDUCES MAINTENANCE COSTS.

• CONVERSELY A TAILWIND WILL INCREASE THE LENGTH OF RUNWAY REQUIRED, SO REDUCING THE AMOUNT OF PAYLOAD WHICH CAN BE CARRIED OR REQUIRE A HIGHER ENGINE POWER SETTING TO BECOME AIRBORNE. THE BOEING 747-400 HAS EITHER A 10 OR 15 KNOT MAXIMUM TAILWIND COMPONENT, DEPENDING ON THE AIRCRAFT’S WEIGHT.

• CROSSWINDS PRIMARILY AFFECT THE PILOT’S AND NOT AIRCRAFT PERFORMANCE, AS THE STRONGER THE CROSSWIND THE BETTER THE PILOT’S SKILLS NEED TO BE, AS WE CAN SEE IN THIS NEXT VIDEO!

CROSSWIND LANDING VIDEO.

HURRICANES, TYPHOONS AND CYCLONES………THEY ARE ALL THE SAME TYPE OF WEATHER SYSTEMS.

Hurricanes are tropical cyclones that have an organized circulation, with sustained winds exceeding 74 mph.

Hurricanes develop over tropical waters. Tropical cyclones forming in the Atlantic and Eastern Pacific are called Hurricanes.While in the Western Pacific they are called Typhoons.And in the Indian Ocean they are called Cyclones.

Typhoons affecting Hong Kong or China and Cyclones affecting India or Bangladesh; can affect our flight operations as the weather can be severe enough to close airports. Due to strong winds and torrential rain, so we must be aware and plan accordingly whenever these are forecast on our planned flight routes.

INTERNATIONAL STANDARD ATMOSPHERE. (I.S.A)

AIRCRAFT PERFORMANCE MANUALS AND TABLES ARE PRIMARILY BASED ON THE MODEL OF THE ‘INTERNATIONAL STANDARD ATMOSPHERE’, AS MEANS OF PROVIDING A WORLD WIDE REFERENCE SYSTEM FOR STANDARDISING AIRCRAFT EQUIPMENT AND PERFORMANCE.

IT CAN BE DESCRIBED AS FOLLOWS:

The ISA model divides the atmosphere into layers with linear temperature distributions. The other values are computed from basic physical constants and relationships.

Thus the standard consists of a table of values at various altitudes, plus some formulas by which those values were derived. For example, at sea level the standard gives a pressure of 1013.25 Hectopascals and a temperature of 15 Celsius, and an initial lapse rate of roughly −2 °C/1,000 ft).

The tabulation continues to 11 km (The Tropopause, as we discussed earlier) where the pressure has fallen to 226.32 Hectopascals and the temperature to −56.5 °C.

Between 11 km and 20 km the temperature is assumed to remain constant.

ICING HOW IT’S FORMED AND AFFECTS US IN AVIATION.

Obviously ice on an aircraft can have a serious affect on aircraft performance and safety.

Many aircraft have crashed due to the aircraft having ice stuck to it’s wings.

We all need to know what to look for and plan ahead.

In aviation we have a ‘clean wing concept’, such that no aircraft can depart with ice on the top surface of the wings…this is forbidden.

So plans need to be made to compensate for this scenario and these plans and procedures can be found in the Company De-Icing Manual and the Silkway Operations Manual Part A.

STRUCTURAL ICING.

Two conditions are necessary for structural icing in flight:

• The aircraft must be flying through visible water such as rain or cloud droplets, and • The temperature at the point where the moisture strikes the aircraft must be 0°C or colder.

Aerodynamic cooling can lower temperature of a wing to 0° C even though the ambient temperature is a few degrees warmer.

Super-cooled water increases the rate of icing and is essential to rapid accretion. Super-cooled water is in an unstable liquid state; when an aircraft strikes a super-cooled drop, part of the drop freezes instantaneously.

The types of structural icing are• Clear ice.• Rime ice.• And a mixture of the two.

Each type has its identifying features.

CLEAR ICE.

Clear ice forms when after initial impact, the remaining liquid portion of the drop flows out over the aircraft surface gradually freezing as a smooth sheet of solid ice. This type forms when drops are large as in rain or in cumuliform clouds.

Clear ice is hard, heavy, and tenacious. Its removal by de-icing equipment is especially difficult.

RIME ICE. Rime ice forms when drops are small, such as those in stratified clouds or light drizzle.

The liquid portion remaining after initial impact freezes rapidly before the drop has time to spread over the aircraft surface.

The small frozen droplets trap air between them giving the ice a white appearance.

THE FOLLOWING IS AN EXCERPT FROM SILKWAY AIRLINE’S OPERATIONS MANUAL PART A.

2.4 DE-ICING AND ANTI-ICING ON THE GROUND. 2.4.1 Background information. The clean aircraft concept must be understood as an important part of the safety of the flight. A clean aircraft is considered to be either totally clean or cleaned and protected with de- icing/anti-icing fluids that still protect the surface and are able to perform aerodynamically correct. When aircraft surfaces are contaminated by frozen moisture of any type, they shall be de-iced prior to dispatch.

When freezing precipitation exists and there is a risk of precipitation ice, snow or frost forming on critical surfaces at the time of dispatch the aircraft must be anti-iced. If both de-icing and anti-icing is required, the procedure may be performed in one or two steps.

The selection of a one or two step procedure depends upon weather conditions, available equipment, available fluids and the Holdover Time to be achieved.

In a one step procedure only the de-icing procedure applies and in a two step procedure both the anti-icing and de-icing procedures apply.

De-icing refers to the removal of frost, snow, ice or slush already accumulated on an aircraft in order to provide clean surfaces.

The fluid is applied hot at a minimum of 60 °C and a maximum of 92°C.

Anti-icing refers to the preventative treatment aircraft surfaces undergo to keep them clear of snow or ice accumulation for a limited period of time (Holdover Time). The fluid is applied cold.

A clean aircraft may require anti-icing only, however, the continual repeated use of cold anti- icing only should be avoided.

One step De-icing / Anti-icing refers to the removal of light frost or light snow using hot fluid at a minimum of 60° C and a maximum of 92 °C with the fluid providing anti-icing protection for a limited period of time (Holdover Time). Used in less severe weather conditions.

Two step De-icing / Anti-icing refers to firstly, the removal of heavier deposits of frost, ice or snow using hot fluid at a minimum of 60 °C and a maximum of 92 °C, and immediately followed by the application of cold anti-icing fluid which provides protection for a limited period of time (Holdover Time). Used in more severe weather conditions.

‘Holdover Time’ refers to the estimated time where anti-icing fluids remain effective on the aircraft surfaces under certain weather conditions.

These published times should not be considered as absolute minimums or maximums as the actual time of protection may be increased or reduced depending on the particular conditions existing at the time.

These times should be considered as guidelines with the lower limit the estimated time of protection during moderate precipitation and the upper limit the estimated time of protection during light precipitation.

To comply with the clean airplane concept, operators must use de-icing/anti-icing fluids that have holdover times long enough to permit safe winter operations during ground icing conditions and acceptable aerodynamic characteristics.

The holdover tables are straightforward and easy to use. Only four pieces of information are required: • Type of fluid.• Fluid concentration.• Outside Air Temperature (OAT).• Weather conditions.

HOW WE USED TO DE-ICE! BUT NO LONGER….

MODERN METHODS.

AN EXAMPLE OF A HOLD OVER TIME (H.O.T.) TABLE IS INCLUDED IN YOUR HAND-OUTS.

With a one-step de-icing/anti-icing procedure, the holdover time begins at the start of de- icing/anti-icing operation.

With a two-step procedure, the holdover time begins at the commencement of the second (anti- icing) step. The holdover protection runs out:(i) at the commencement of take-off roll or, (ii) when frozen deposits start to form or accumulate on treated aeroplane surfaces.

Aerodynamic areas The wings and the tail are the main concern but also secondary parts such as slats, flaps, ailerons, rudder, elevator and tabs are critical for the correct airflow. It is important that the de-icing crew can identify these parts because the success of removal of contamination and protection from icing has a direct impact on lifting and manoeuvrability. Other aerodynamic parts on an aircraft can be strakes, winglets, pylons, stall strips/vanes, vortex generators...

Aircraft surfaces Lowering slats and flaps exposes new surfaces and leading edges where contamination can adhere. If slats and flaps are in a lowered position while the aircraft is on ground such areas shall be checked and cleaned/protected if necessary.

Contamination on these parts will cause irregular airflow and manoeuvrability problems when they are lowered in flight.

The fuselage is not a critical lifting area but contamination shall be removed in the same manner as other surfaces. The main concern is that snow, slush or ice will break off and damage the engine or aircraft surfaces that can cause a dangerous situation during take-off.

The upper surfaces of the wings and tail are not the only areas to check and treat. The lower surfaces are also highly important.

The wing lower surfaces shall be free of ice.

The horizontal stabilizer lower surface shall be clean in all cases. The horizontal stabilizer creates a lifting force whether up or down depending on how the elevator and tabs is positioned. The tail down force is pronounced during take-off and shall therefore be verified clean on both sides.

Weather effects De-icing/anti-icing procedures and their respective holdover timetables are set according to some weather elements. These tables do not necessarily cover all the phenomena that can be experienced during a winter season but they give a compromise of choices where different elements can be included. Each weather category has its relevant temperature indication range.

These weather categories include: • Active frost.• Freezing fog.• Snow/Snow Grains. • Freezing drizzle (if positive indication of freezing drizzle is not possible, use light freezing holdover rain times.)• Light freezing rain.• Rain on cold soaked wing. Due to cold fuel in the fuel tanks.• Other (heavy snow, snow pellets, ice pellets, hail, moderate freezing rain and heavy freezing rain).

2.4.2 Responsibilities. The person releasing the aeroplane is responsible for the removal of all ice, snow or frost from the aeroplane prior to departure.

The person doing the de-icing of the aeroplane is responsible for the correct and complete de-icing/anti-icing of the aeroplane.This has to be reported to the Commander by naming the AEA anti-icing code.

Commanders are responsible for making the final decision for departure.

The Commander is responsible for the condition of the aeroplane during ground manoeuvring prior to take-off (see guidelines to holdover times).

CAUTIONS.

• The only acceptable decision-making criterion, for take-off without a pre-take-off contamination inspection, is the shorter time within the applicable holdover time table cell.

• The time of protection will be shortened in heavy weather conditions, heavy precipitation rates, or high moisture content.

• High wind velocity or jet blast may reduce holdover time.

• Holdover time may be reduced when aircraft skin temperature is lower than outside air temperature.

• Fluids used during ground de-icing/anti-icing do not provide in-flight icing protection.

WHAT HAPPENS WHEN AN AIRCRAFT IS NOT DE-ICED…..

……………………………IT CRASHES……………………………..

VISIBILITY AND RUNWAY VISUAL RANGE (R.V.R.)

Runway visual range (RVR), in aviation meteorology, is the distance over which a pilot of an aircraft on the centreline of the runway can see the runway surface markings delineating the runway or identifying its centre line. RVR is normally expressed in feet or meters.

RVR is used as one of the main criteria for minima on instrument approaches, as in most cases a pilot must obtain visual reference of the runway to land an aircraft.

The maximum RVR reading is 2,000 metres or 6,000 feet, above which it is not significant and thus does not need to be reported.

RVRs are provided in METARSs and are transmitted by air traffic controllers to aircraft making approaches to allow pilots to assess whether it is prudent and legal to make an approach.

RVR is also the main criteria used to determine the category of visual aids that are installed at an airport.

The International Civil Aviation Organization, ICAO stipulates in its Annex 14 that:

• For RVR values above 550 m, CAT I lighting shall be installed.• If RVR is between 300 m and 549 m then CAT II lighting is required. • CAT IIIa is installed for RVR values between 175 m and 300 m.• CAT IIIb is required for RVR values between 50 m and 175 m.• While there is no RVR limitation for CAT IIIc visual aids.

Originally RVR was measured by a person, either by viewing the runway lights from the top of a vehicle parked on the runway threshold, or by viewing special angled runway lights from a tower at one side of the runway. The number of lights visible could then be converted to a distance to give the RVR. This is known as the human observer method and can still be used as a fall-back.Today most airports use Instrumented Runway Visual Range or IRVR, which is measured by devices called forward scatter meters which provide simplified installation as they are integrated units and can be installed as single unit(s) at a critical location along the runway or transmissometers which are installed at one side of a runway relatively close to its edge. Normally three transmissometers are provided, one at each end of the runway and one at the midpoint.

RUNWAY LIGHTS AND RVR EQUIPMENT.

Converted Meteorological Visibility (CMV).

A value equivalent to an RVR which is derived from the reported meteorological visibility, as converted in accordance with the specified requirements in the CAR.

Conversion of Reported Meteorological Visibility to RVR/CMV Horizontal visibility reported by the meteorological office could be different from the slant visibility observed by the pilot due to factors such as low lying haze and a smoke layer.

The reported visibility has inherent limitations due to the fact that it is reported at a site that is removed from the point at which a pilot makes the approach to land and is expected to acquire the visual reference to continue the approach.

An RVR is a better representation of the expected distance that the pilot may acquire visual cues on approach.

As RVR and meteorological visibility are established differently, a ratio can be identified between the two.

Effect of lighting intensities and background luminance play a role when establishing an RVR. In cases where the RVR is not reported, a pilot may derive RVR/CMV by using a mathematical conversion depending upon the type of approach lighting and day/night conditions.

PILOTS SPEND A LOT OF THEIR TIME TALKING ABOUT THE WEATHER!

AVIATION WEATHER AND HOW IT IS PRESENTED.

The most common methods for presenting aviation weather is as follows:

• METAR For reporting actual weather conditions at airfields and airports.

• TAF For reporting Terminal Aviation Forecasts.

• SNOWTAM For reporting runway conditions if contaminated by snow or slush.

• RUNWAY REPORTS For reporting airport runway conditions, which can include contamination by water or snow.

METAR DECODE.

The following is an example METAR from Burgas Airport, Bulgaria. It was taken on 4 February 2005 at 16:00 (UTC).

METAR LBBG 041600Z 12003MPS 310V290 1400 R04/P1500N R22/P1500U +SN BKN022 OVC050 M04/M07 Q1020 NOSIG 9949//91=

METAR indicates that the following is a standard hourly observation.

LBBG is the ICAO airport code for Burgas airport.....UBBB Incidentally UBBB IS THE icao code for Baku airport.

041600Z indicates the time of the observation. It is the day of the month (the 4th) followed by the time of day 1600 Zulu time, which equals 4:00 pm Greenwich Mean Time.

12003MPS indicates the wind direction is from 120° (east-southeast) at a speed of 3 MPS (6 Knots). Speed measurements can vary from knots (KT) or meters/second (MPS).

310V290 indicates the wind direction is varying from 310° true (northwest) to 290° true (west-northwest).

1400 indicates the prevailing visibility is 1,400 m.

R04/P1500N indicates the Runway Visual Range (RVR) along runway 04 is 1,500 m and not changing significantly.

R22/P1500U indicates RVR along runway 22 is 1,500 m and rising.

+SN indicates snow is falling at a heavy intensity. If any precipitation begins with a minus or plus (-/+), it's either light or heavy.

BKN022 indicates a broken (over half the sky) cloud layer with its base at 2,200 ft (AGL). The lowest "BKN" or "OVC" layer specifies the cloud ceiling.

OVC050 indicates an unbroken cloud layer (overcast) with its base at 5,000 ft (1,500 m) above ground level.

M04/M07 indicates the temperature is −4 °C and the dew-point is −7 °C. An M in front of the number indicates that the temperature/dew-point is below zero (0) Celsius.

Q1020 indicates the current altimeter setting QNH is 1,020hPa.

NOSIG is an example of a TREND forecast which is appended to METARs at stations while a forecaster is on watch. NOSIG means that no significant change is expected to the reported conditions within the next 2 hours.

9949//91 indicates the condition of the runway: 99 indicates either a specific runway (e.g. 25 = Rwy 25 or 25L; adding 50 will indicate Right Runway) or all the airport's runways ("99"). Some locations will report the runway using 3 characters (e.g. 25L)4 means the runway is coated with dry snow9 means 51% to 100% of the runway is covered// means the thickness of the coating was either not measurable or not affecting usage of the runway91 means the braking index is bad, in other words the tires have bad grip on the runway

CAVOK is an abbreviation for Ceiling And Visibility OKay, indicating no cloud below 5,000 ft or the highest minimum sector altitude and no cumulonimbus or towering cumulus at any level, a visibility of 10 km or more and no significant weather.

= indicates the end of the METAR report

YOU HAVE A HANDOUT WHICH EXPLAINS ALL THE DIFFERENT TYPES OF CODES FOR WEATHER TYPES AND CONDITIONS WHICH CAN BE REPORTED.

WHY PILOTS NEED WEATHER FORECASTS.

T.A.F. (TERMINAL AREA FORECAST)

TAFs apply to approximately five statute miles (about 4.3 nautical miles or 8 km) radius from the centre of the airport runway complex.

Generally, TAFs apply to a 24-hour period; and, as of November 5, 2008, TAFs for many major airports cover 30-hour periods.

The date/time group reflects the new 24- or 30-hour period in Coordinated Universal Time (UTC), as always.

TAFs complement and use similar encoding to METAR reports.

T.A.F. RULES.

TAFs must follow a set of rules that define what must be placed in each line and what criteria require a new line.

There are four different lines in a TAF. The first one gives location, valid time and given weather for that time until the next line of the forecast.

A BECMG (becoming) line (not used in TAFs issued in the United States) indicates that in the period given, the weather will start to change from the previous line to the next line.

An FM (from) line indicates that after the given time, the weather will be what the line states.

The change-indicator group TEMPO is used to indicate temporary fluctuations to forecast meteorological conditions which are expected to have a high percentage (greater than 50%) probability of occurrence, last for one hour or less in each instance and, in the aggregate, cover less than half of the period.

WE WILL NOW LOOK AT AN EXAMPLE OF A TAF AS IT APPLIES TO AN AIRPORT IN THE USA. AS YOU WILL SEE THERE IS VERY LITTERAL DIFFERENCE TO THE CODES, ONLY THAT INSTEAD OF VISIBILITY IN NAUTICAL MILES, IT IS STATED IN FEET OR STATUTE MILES.

This TAF is an example of a 30-hour TAF, released on November 5, 2012 at 1730 UTC:

KJFK 051730Z 0518/0624 31008KT 3SM -SHRA BKN020 FM052300 30006KT 5SM -SHRA OVC030 PROB30 0604/0606 VRB20G35KT 1SM TSRA BKN015CB FM060600 25010KT 4SM -SHRA OVC050 TEMPO 0608/0611 2SM -SHRA OVC030 RMK NXT FCST BY 00Z=

The first line contains identification and validity times.

KJFK indicates the airport to which the forecast applies (ICAO airport code). New York’s JFK airport in this example.

051730Z indicates that the report was issued on the 5th of the month at 1730 UTC (also known as Zulu, thus the "Z").

0518/0624 indicates that the report is valid from the 5th at 1800 UTC until the 6th at 2400 UTC.

The remainder of the first line contain the initial forecast conditions. Variations of the codes used for various weather conditions are many.

31008KT indicates that the wind will be from 310 degrees true at 8 knots.

3SM -SHRA BKN020 indicates that visibility will be 3 statute miles in light (-) showers (SH) of rain (RA), with a broken ceiling (between 5/8 and 7/8 of the sky covered) at 2,000 feet AGL.

Each line beginning with FM starts a new forecast period.

FM052300 indicates the next period lasts from (FM) the 5th at 2300 UTC to the 6th at 0600 UTC (the effective time on the next "FM" line). The remainder of the line has similar formatting to the other forecast lines.

The final line is for errata, comments, and remarks.RMK NXT FCST BY 00Z indicates a remark that the next forecast will be issued by 0000 UTC.

WE CAN DECODE THE REST OF THE TAF OURSELVES WITH THE HANDOUT WHICH YOU HAVE.

A trend forecast is a truncated version of a TAF giving the expected conditions in a two hour period following the issue of an observation. This short period forecast is appended to the end of a METAR.

METAR EGYM 291350Z 29010KT 8000 -RADZ FEW010 SCT037 OVC043 10/07 Q1008 BLU TEMPO 7000 -RADZ SCT020 WHT=

In this example the METAR indicates it is from EGYM (RAF Marham) at 1350 UTC on the 29th. The observation follows the METAR (see METAR for explanation), with the Trend added to the end of the observation.

The Trend reads TEMPO 7000 -RADZ SCT020 WHT

Temporary deterioration to 7 km visibility in light rain or drizzle with cloud scattered at 2000 ft, colour state White.

Colour states are generally used for observations at military airfields to depict in a ‘colour’ code the status of both cloud base and visibility.

A TABLE STATING THESE COLOUR CODES IS INCLUDED IN YOUR HANDOUTS.

Trends are not used in the United States.

Colour state BLU WHT GRN YLO1 YLO2 AMB RED

Cloud height in feet

2500 1500 700 500 300 200 <200

Visibility in metres 8000 5000 3700 2500 1600 800 <800

If an airfield runway is unusable for reasons other than clouds or low visibility, e.g. ice or other obstructions, then the word BLACK is written in full and placed immediately before the actual colour state e.g. BLACKWHT.

MILITARY AIRPORT COLOUR CODES.

1500

5000

SNOWTAM

A SNOWTAM is a message describing the conditions of the runways, taxiways and apron at an aerodrome.

A SNOWTAM is valid for 24 hours, but there are rules stating that a new SNOWTAM shall be issued sooner if significant changes occur.

SNOWTAM and MOTNE RWY reports are only provided for winter conditions (snow, ice etc) but not for other hazardous RWY conditions e.g. RWY slippery when wet or, wet combined with dust. Observations and measurements are made at routine intervals but only when RWY are contaminated and/or when there are significant changes.

There are certain definitions used in SNOWTAM.

DAMP - The surface shows a change of colour due to moisture.WET - The surface is soaked but there is no standing water.WATER PATCHES - Significant patches of standing water are visible.STANDING WATER - Standing water of significant depth and area which affects the braking action.FLOODED - Extensive standing water is visible.DRY SNOW - Snow which can be blown if loose. If compacted by hand, will fall apart again upon release.WET SNOW - Snow which, if compacted by hand will stick together and tend to form a snowball.SLUSH - Water saturated snow.COMPACTED SNOW -Snow which has been compressed into a solid mass that resists further compression and will hold together or break up into chunks if picked up.

SNOWTAM EXAMPLE.

A)LSZH B)11070620 C)10 D)2200 E)40L F)4/5/4 G)20/10/10 H)30/35/30 J)30/5L K)YES L L)TOTAL M)0900 P)YES 12 S)11070920 T)FIRST 300M RWY 10 COVERED BY 50 MM SNOW, RWY CONTAMINATION 100%

NOW WE WILL DECODE IT!

A) LSZH AERODROME LOCATION INDICATOR--------------------------------------------------------------------------------B) 11070620 DATE/TIME OF OBSERVATION (in UTC)--------------------------------------------------------------------------------C) 10 RUNWAY DESIGNATORS--------------------------------------------------------------------------------D) 2200 CLEARED RUNWAY LENGTH, if less than published length (m).--------------------------------------------------------------------------------E) 40L CLEARED RUNWAY WIDTH, if less that published. (m; if offset left or right of centre line add "L" or "R").--------------------------------------------------------------------------------F) 4/5/4 DEPOSITS OVER TOTAL RUNWAY LENGTH (Observed on each third of the runway starting from threshold having the lower runway designation number).

NIL - CLEAR AND DRY 1 - DAMP 2 - WET 3 - RIME OR FROST 4 - DRY SNOW 5 - WET SNOW 6 - SLUSH 7 - ICE 8 - COMPACTED SNOW 9 - FROZEN RUTS OR RIDGES

G)20/10/20 MEAN DEPTH (mm) FOR EACH THIRD OF TOTAL RUNWAY LENGTH.--------------------------------------------------------------------------------H)30/35/30 FRICTION MEASUREMENT ON EACH THIRD OF RUNWAY AND FRICTION MEASURING DEVICE.

MEASURED or CALCULATED COEFFICENT

0.40 and above 0.39 - 0.36 0.35 - 0.30 0.29 - 0.26 0.25 and below

OR:

9 ESTIMATED SURFACE FRICTION

5 - GOOD 4 - MEDIUM/GOOD 3 - MEDIUM 2 - MEDIUM/POOR 1 - POOR 9 - Unreliable

J) 30/5L CRITICAL SNOWBANKS. If present, insert height (cm) / distance from the edge of runway (m) followed by L or R or LR if applicable.--------------------------------------------------------------------------------K) YES L RUNWAY LIGHTS (If obscured insert YES followed by L or R or both LR if applicable.--------------------------------------------------------------------------------L) TOTAL FURTHER CLEARANCE (If planned insert length (m) / width(m) to be cleared or if full dimensions insert TOTAL.--------------------------------------------------------------------------------M) 0900 FURTHER CLEARANCE EXPECTED TO BE COMPLETED BY...(UTC).--------------------------------------------------------------------------------N)...TAXIWAY (if no appropriate taxiway is available, insert NO).--------------------------------------------------------------------------------P) YES 12 TAXIWAY SNOWBANKS (If more than 60 cm, insert "YES" followed by distance apart, m)--------------------------------------------------------------------------------S) 11070920 NEXT PLANNED OBSERVATION/MEASUREMENT IS FOR (month/day/hour UTC).--------------------------------------------------------------------------------T) First 300M RWY 10 covered by 50 mm PLAIN LANGUAGE REMARKS (Including contaminant coverage and other significant information like sanding or de-icing).

ADVERSE WEATHER CONDITIONS IN THE MIDDLE EAST AND ASIA.

IN OTHER WORDS, THE TWO REGIONS WHICH WE OPERATE IN THAT HAS THE MOST DIFFICULT WEATHER CONDITIONS. A FACT WHICH YOU NEED TO HAVE SOME KNOWLEDGE ON AS BEING RESPONSIBLE FOR ASSISTING IN THE DISPATCH OF OUR AIRCRAFT.

WE WILL START WITH THE MIDDLE EAST, AND INCLUDE AZERBAIJAN AS BEING A PART OF THIS REGION.

MIDDLE EAST REGION.

NOVEMBER TO APRIL

COLD FRONTS FROM THE WEST PRODUCE CB’S (THUNDERSTORMS) AND SQUALL LINES OVER THE EASTERN MEDITERRANEAN SECTORS, OCCASIONALLY REACHING AS FAR AS TEHRAN.

WARM FRONTS MAY AFFECT THE ROUTES TO TEHRAN AND BAGHDA, ROUTES WHICH SILKWAYS CURRENTLY OPERATE OVER.FOR EXAMPLE, BAKU TO DUBAI AND CONVERSELY DUBAI TO BAKU.

THESE WARM FRONTS MOVE FROM THE SOUTHEAST TO THE NORTHWEST, WITH THE WARM AIR COMING FROM THE PERSIAN GULF AREA.THEY PRODUCE OVERCAST CONDITIONS WITH RAIN, DRIZZLE AND OCCASIONAL SNOW. EAST OF THE TEHRAN/PERSIAN GULF AREA, FRONTAL PASSAGES ARE RARE.

IF THEY OCCUR THEY PRODUCE CUMULUS CLOUDS AND SCATTERED THUNDERSTORMS.

JET STREAMS AND UPPER WINDS

JET STREAMS ARE TO BE FOUND OVER THE WHOLE OF THE MIDDLE EASTERN AREA. THE MAIN DIRECTION IS FROM THE WEST, OCCASIONALLY FROM THE SOUTH WEST.

WE NEED TO BE AWARE THAT WIND FORECASTS CAN OFTEN BE WRONG DUE TO THE MOVEMENT OF THE JETSTREAM AREAS.

AVERAGE STRENGTH 60-90 KNOTS, MAXIMUM BEING 120-150 KNOTS.

CLEAR AIR TURBULENCE (C.A.T.) CAN OCCUR IN CONNECTION WITH THESE JETSTREAMS.

MOUNTAIN WAVE ACTIVITY MAY OCCUR OVER BEIRUT-ANKARA-TEHRAN, DUE TO THE HIGH MOUNTAINOUS TERRAIN.

ISOLATED THUNDERSTORMS MAY OCCUR, ESPECIALLY IN MAY, THEY USUALLY HAVE A BASE OF AROUND 6,000 FEET ABOVE GROUND LEVEL, MOVING SLOWLY TO THE NORTH EAST.

DUST AND SANDSTORMS OCCUR IN THE REGION OF EGYPT, SYRIA, IRAQ, IRAN, PERSIAN GULF AREA AND PAKISTAN.THESE ARE OFTEN ASSOCIATED WITH GUSTY THUNNDERSTORMS OR FRONTAL WINDS, WHEN THE SURFACE WINDS ARE GREATER THAN 20-25 KNOTS.IN THESE STORMS THE AIR IS FILLED WITH DUST/SAND PARTICLES UP TO 15,000 FEET. THESE CAN OCCUR AT ANY TIME OF THE YEAR BUT ARE MOST FREQUENT DURING THE SPRING, SUMMER AND AUTUMN.

MIDDLE EAST REGION (CONTINUED).

MAY TO OCTOBER.

FRONTAL ACTIVITY OVER THE MAJORITY OF THE ROUTES WE OPERATE DOES NOT OCCUR, EXCEPT FOR SOME WEAK SYSTEMS AFFECTING ISTANBUL AND ANKARA. GOOD WEATHER CAN BE EXPECTED WITH MOSTLY CLEAR SKIES.

JET STREAMS AND UPPER WINDS

THESE ARE LIGHT WESTERLY WINDS BECOMING VARIABLE IN THE PERSIAN GULF AREA AND NORTH EAST TO SOUTH EAST TOWARDS KARACHI.

THE APPROACH PATH TO AIRPORTS IN THE MIDDLE EAST AND GULF DESERT AREAS ARE SOMETIMES ACCOMPANIED BY VERY STRONG WINDSHEARS OR INVERSIONS.(AN INVERSION IS WHERE THE TEMPERATURE IN THE LOWER ALTITUDES STARTS TO INCREASE WITH ALTITUDE AND NOT DECREASE, AS WE WOULD NORMALLY EXPECT.)

TROPICAL CYCLONES MOVE IN FROM THE ARABIAN SEA AND MAY OCCASIONALLY AFFECT THE KARACHI AREA.

DUST AND SANDSTORMS ARE MORE FREQUENT DURING THESE SUMMER MONTHS.

THE ITF (INTER-TROPICAL FRONT), KNOWN AS A MONSOON MAY REACH AS FAR AS KARACHI IN MID-SUMMER, THOUGH NOT EVERY YEAR.

FAR EAST REGION

TYPHOONS AND CYCLONES.

A TROPICAL CYCLONE CONSISTS OF A ROTATING MASS OF WARM HUMID AIR NORMALLY BETWEEN 200 AND 1000 MILES IN DIAMETER. THE ATMOSPHERIC PRESSURE IS LOWEST NEAR THE CENTRE, AND WILL BE LESS THAN 990 MILLIBARS IN TROPICAL CYCLONES THAT HAVE DEVELOPED TO TYPHOON INTENSITY.IN THE NORTHERN HEMISPHERE THE WINDS OF A CYCLONIC CIRCULATION SPIRAL INWARDS TOWARDS THE CENTRE IN AN ANTI-CLOCKWISE DIRECTION.

WELL DEVELOPED TROPICAL CYCLONES HAVE WIDESPREAD AREAS OF THICK CLOUD EXTENDING TO GREAT HEIGHTS. THE STRONGEST WINDS, WHICH MAY REACH 200 KNOTS, BLOW IN A TIGHT BAND AROUND THE EYE OF A TROPICAL CYCLONE.

THE EYE IS A CENTRAL REGION OF LIGHT WINDS AND LIGHTLY CLOUDED SKY, USUALLY CIRCULAR OR ELIPTICAL IN SHAPE AND RANGING FROM A FEW MILES TO OVER 80 MILES IN DIAMETER.

WINDS DIMINISH RAPIDLY WITH DISTANCE FROM THE CENTRE OF THE EYE.

WINDS RARELY EXCEED 60 KNOTS MORE THAN 50 MILES AWAY FROM THE CENTRE.

VIEW OF A TROPICAL CYCLONE APPROACHING HONG KONG.

THE TERM TROPICAL CYCLONE DOES NOT IMPLY ANY PARTICULAR INTENSITY. THE MOST INTENSE ARE TYPHOONS.

THE INTERNATIONAL CLASSIFICATION OF THESE WEATHER SYSTEMS ARE AS FOLLOWS:

• TROPICAL DEPRESSIONS HAVE A MAXIMUM STEADY WIND OF UP TO 33 KNOTS GUSTING TO 50 KNOTS.

• TROPICAL STORMS HAVE A MAXIMUM STEADY WIND OF UP TO 47 KNOTS GUSTING TO 75 KNOTS.

• SEVERE TROPICAL STORMS HAVE A MAXIMUM STEADY WIND OF 63 KNOTS GUSTING UP TO 100 KNOTS.

• TYPHOONS HAVE A MAXIMUM STEADY WIND IN EXCESS OF 64 KNOTS GUSTING ABOVE 100 KNOTS.

ALL OF THE ABOVE WEATHER SYSTEMS CAN HAVE A SEVERE IMPACT ON OUR FLIGHT OPERATIONS CAUSING EITHER DELAYS, DIVERSIONS OR CANCELLATIONS OF FLIGHTS.

THEREFORE THERE IMPACT NEEDS TO BE UNDERSTOOD.

THE TRACK OF A TYPHOON APPROACHING HONG KONG.

AVIATION ACCIDENTS RELATING TO AIRCRAFT FLYING INSIDE A TYPHOON.

OCCURRENCE OF TROPICAL CYCLONES.

TROPICAL CYCLONES CAN OCCUR OVER THE SOUTH CHINA SEA AT ANY TIME OF THE YEAR, ALTHOUGH THERE ARE OVER 30 TIMES AS MANY IN SEPTEMBER AS IN FEBRUARY.NOT ALL AT ONE TIME BUT STATISTICALLY OVER THE YEARS!

THE MAJORITY OCCURS IN THE SUMMER AND AUTUMN, WITH A PRONOUNCED MAXIMUM IN AUGUST AND SEPTEMBER.

NO TROPICAL CYCLONE HAS BEEN KNOWN TO CAUSE GALES IN HONG KONG DURING THE MONTHS DECEMBER TO APRIL.

ON AVERAGE 5 OR 6 TROPICAL CYCLONES THREATEN HONG KONG EACH YEAR.

ABOUT ONCE IN EVERY 10 YEARS THE CENTRE OF A FULLY DEVELOPED TYPHOON PASSES SUFFICIENTLY CLOSE TO HONG KONG TO CAUSE WIND SPEEDS OF 65 KNOTS OR MORE.

ALTHOUGH TROPICAL CYCLONES WEAKEN OVER LAND, AS THEY ARE NOT RECEIVING ENERGY FROM THE WARM SEAS, THEY GENERALLY DO NOT DIE OUT FOR SEVERAL DAYS. THEY HAVE BEEN KNOWN TO TRAVEL HUNDREDS OF MILES ACROSS MAINLAND CHINA.

TO CLOSE THIS MODULE ON METEOROLOGY THE FOLLOWING ARE TWO VIDEOS SHOWING AIRCRAFT LANDING IN A TYPHOON IN HONG KONG.

ENJOY!

THERE IS A SAYING IN AVIATION WHICH GOES…….

“IT IS BETTER FOR A PILOT TO BE ON THE GROUND WISHING HE WAS IN THE AIR!

THAN BEING IN THE AIR AND WISHING HE WAS ON THE GROUND!”