Air navigation
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AIR NAVIGATION. Part 5. Weather. LEARNING OUTCOMES. On completion of this lesson, you should:. - Know the hazards that weather presents to aviation. Weather. Introduction. You will have previously studied the weather as it relates to walking in the hills.

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Air navigation

AIR NAVIGATION

Part 5

Weather


Learning outcomes

LEARNING OUTCOMES

On completion of this lesson, you should:

  • - Know the hazards that weather presents to

  • aviation.


Air navigation

Weather


Introduction

Introduction

You will have previously studied the weather as it relates to walking in the hills.

It is the same weather that affects aircraft operations but with one major difference

Icing is a far more serious problem for an aircraft than it is for a walker


Meteorological conditions

Meteorological Conditions

Simple aircraft such as basic trainers are not equipped with instruments to enable them to safely fly in cloud or fog

The student pilot does not have the experience to fly in fog or cloud.

Consequently, it is necessary to define the weather conditions in which beginners may fly.


Meteorological conditions1

Meteorological Conditions

These weather conditions are called

Visual Met Conditions

VMC

A simplified version of the rules are set out in the following table


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ABOVE 3000’ BELOW 3000’

Visibility - 8 KM

Visibility - 5 KM

distance FROMcloud:

1000’ vertically

1500m horizontally

distance FROMcloud:

1000’ vertically

1500m horizontally

NB AIRCRAFT FLYING BELOW

140 KTS AND IN SIGHT OF THE

GROUND MAY USE 1 KM

VISIBILITY AND MERELY KEEP

CLEAR OF THE CLOUD


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Meteorological Conditions

It follows that if an aircraft flies in weather worse than shown in the table, it must have the necessary instruments to fly in or near to cloud or in poor visibility.

This weather is known as Instrument Met Conditions

IMC

Only aircraft with suitable equipment and pilots with suitable instrument ratings may fly in IMC


The visual circuit

The Visual Circuit

In the early stages of flying, a trainee pilot will not want to lose sight of the runway when flying circuits in order to practice take-offs and landings

To achieve this, VMC is needed and normally the aerodrome controller will decide if the weather is good enough


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The Visual Circuit

If the circuit height is 1000’ then the lowest cloud base will need to be above this

(usually 1500’)

and the visibility will need to be good enough

to be able to see the runway from anywhere

in the circuit

(usually 5 km)


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THE VISUAL CIRCUIT 2

1500’ CLOUDBASE

5 KM VISIBILITY

2 6


Surface wind

Surface Wind

We have already looked at the effects of wind & drift, when transiting from A- B.

On the airfield we must also note the effect of surface wind.


Surface wind1

Surface Wind

If conditions are not completely calm, we need to know the wind direction & strength, so we take off & land into the wind

You hopefully will remember that takeoffs & landings into the wind are shorter !


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Surface Wind

It is very rare to find the wind blowing exactly along the runway.

(even though runway directions are chosen along the line of the prevailing wind)

Normally the wind will blow partly across the runway, so we need to calculate cross wind & headwind

To find this you can draw a vector, use a table or a simple mental method, as we shall see.


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THE VECTOR

6 0

Angle Off

TAKE OFF

Runway 09

HEAD

WIND

15 KNOTS

40

SURFACE WIND

130/20 KNOTS

50

90°- Angle Off =

2 7

CROSSWIND

COMPONENT

13 KNOTS


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  • .

Angle between wind direction & runway heading for crosswind

component

THE TABLE

10

20

30

40

50

60

70

80

90

W

i

n

d

s

p

e

e

d

i

n

K

n

o

t

s

5 1 2 2 3 4 4 4 5 5

This is a standard table to enable you to work out the wind component

10 2 35 6 7 8 9 9 10

15 3 5 7 9 11 13 14 14 15

20 3 7 10 13 15 17 18 19 20

25 4 8 12 16 19 22 23 24 25

30 5 10 15 19 23 26 28 29 30

Note: these angles

are from the vector

triangle shown

minus angle off

80 70 60 50 40 30 20 10 0

For headwind component - Angle between wind direction and

runway heading


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Wind Component

To use the table you need the angle between the runway heading & the wind direction (angle off)

If it is 40 degrees, to obtain the crosswind component you use the top row of angles, find the 40 degree column, & follow it until you get to the windspeed, in this case 20 knots.


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Angle between wind direction & runway heading for crosswind

component

10

20

30

40

50

60

70

80

90

W

i

n

d

s

p

e

e

d

i

n

K

n

o

t

s

5 1 2 2 3 4 4 4 5 5

10 2 35 6 7 8 9 9 10

15 3 5 7 9 11 13 14 14 15

20 3 7 10 13 15 17 18 19 20

25 4 8 12 16 19 22 23 24 25

30 5 10 15 19 23 26 28 29 30

Note: these angles

are from the vector

triangle shown

minus angle off

80 70 60 50 40 30 20 10 0

For headwind component - Angle between wind direction and

runway heading

This gives the cross wind component as 13 knots

40

20

You use the bottom angles if you want to know the headwind


The quick method

ANGLE BETWEEN WIND DIRECTION AND RUNWAY HEADING FOR CROSS WIND COMPONENT

ZERO

1/4 WIND STRENGTH

1/2 WIND STRENGTH

3/4 WINDSTRENGHT

FULL WIND STRENGTH

DEGREES

0-15

15-30

30-45

45-60

60-90

The Quick Method

This is somewhat easier & and definitely quicker


Shallow fog

Shallow Fog

As fog starts to form in the early evening, there is often a shallow layer, a few feet thick, next to the ground.

A pilot in the circuit, especially at night may not even notice this as the ground & lights are clearly visible

However once in the approach on the glide slope the fog will appear to be much thicker, & prevent the aircraft from landing as the runway or lights will no longer be visible.


Shallow fog1

UNDER 800 METRES? ABORT!

Shallow Fog

This slant visibility can be measured & if the runway visual range ( RVR ) is under 800 metres a safe landing is unlikely.


Precipitation

Precipitation

This is a fancy word for rain! Covers rain, sleet, snow, hailetc

It causes the following problems:

Leaks into aircraft on the ground

Once a fluid has frozen on the airframe it must be removed with de icing fluid

Floods runways

If it is frozen it can stick to the airframe and cause takeoff problems


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Aircraft De-Icing


Airborne hazards

Airborne Hazards

Apart from thunderstorms, the main hazard is ice

Even in VMC icing can form on an airframe at certain temperatures.


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Icing

TEMPERATURE

ICE !

This can be fatal, but why ?


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Icing

In a car the main problem on a frosty morning is the frozen windscreen

In an aircraft this is easily cured by heating the

windscreen.

But you cannot heat the whole of the airframe

So the ice will stick to the surface.


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Icing

On the wings this means the shape of the wing changes & will eventually cease to be an aerofoil

Ice on leading edge

WING


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Icing

However this is not all. As the ice gathers on the airframe the weight increases

This means that lift will not support the weight of the aircraft plus the ice & eventually the aircraft will fly like a brick


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Icing

Icing can also affect other aspects of the aircrafts operations, such as undercarriages, controls surfaces, and radio aerials

It will also affect engine operation, so the best advice is to stay away from icing


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