2 LEARNING OUTCOMES On completion of this unit, you should: Be able to carry out calculations to determine aircraft distance, speed and timeUnderstand the principles of vectors and the triangle of velocities to establish an aircraft’s track and ground speed
3 LEARNING OUTCOMES Understand the principles of the 1 in 60 rule Understand the types of compass systems used for air navigation, how they work and their limitationsKnow the hazards that weather presents to aviation
5 IntroductionYou 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 differenceIcing is a far more serious problem for an aircraft than it is for a walker
6 Meteorological Conditions Simple aircraft such as basic trainers are not equipped with instruments toenable them to safely fly in cloud or fogThe student pilot does not have the experience to fly in fog or cloud.
7 Meteorological Conditions Consequently, it is necessary to define the weather conditions in which beginners may fly.These are called
8 Visual Met Conditionsa simplified version of the rules are set out in the following tableVMC
9 ABOVE 3000’ BELOW 3000’Visibility - 8 KMVisibility - 5 KMdistance FROM cloud:1000’ vertically1500m horizontallydistance FROM cloud:1000’ vertically1500m horizontallyNB AIRCRAFT FLYING BELOW140 KTS AND IN SIGHT OF THEGROUND MAY USE KMVISIBILITY AND MERELY KEEPCLEAR OF THE CLOUD
10 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.
11 This weather is known as Instrument Met Conditions Only aircraft with suitableequipment andpilots with suitable instrument ratings may fly in IMCIMC
12 The Visual CircuitIn 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 landingsTo achievethis, VMC is needed and normally the aerodrome controller will decide if the weather is good enough
13 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)
14 THE VISUAL CIRCUIT 22 65 KM VISIBILITY1500’ CLOUDBASE
15 On the airfield we must also note the effect of 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.
16 Surface WindIf conditions are not completely calm, we need to know the wind direction & strength, so we take off & land into the windYou hopefully will remember that takeoffs & landings into the wind are shorter !
17 It is very rare to find the wind blowing exactly along the runway Wind ComponentNormally the wind will blow partly across the runway, so we need to calculate cross wind & headwindIt is very rare to find the wind blowing exactly along the runway(even thought runway directions are chosen along the line of the prevailing wind)To find this you can draw a vector, use a table or a simple mental method, as we shall see.
18 THE VECTOR Angle Off 90°- Angle Off = 6 0 TAKE OFF HEAD 40 WIND 15 KNOTS40SURFACE WIND130/20 KNOTS5090°- Angle Off =2 7CROSSWINDCOMPONENT13 KNOTS
19 This is a standard table to enable you to work out the wind component .Angle between wind direction & runway heading for crosswindcomponentTHE TABLE102030405060708090WindspeKotThis is a standard table to enable you to work out the wind componentNote: these anglesare from the vectortriangle shownminus angle offFor headwind component - Angle between wind direction andrunway heading
20 To use the table you need the angle between the runway heading & the wind direction (angle off)
21 If it is 40 degrees you 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.
22 This gives the cross wind component as 13 knots 40 104050607080902030Angle between wind direction & runway heading for crosswindcomponentWindspeKotFor headwind component - Angle between wind direction andrunway headingNote: these anglesare from the vectortriangle shownminus angle offThis gives the cross wind component as 13 knots4020You use the bottom angles if you know the headwind
23 This is somewhat easier & and definitely quicker The Quick MethodANGLE BETWEEN WIND DIRECTION AND RUNWAY HEADING FOR CROSS WIND COMPONENTDEGREES0-1515-3030-4545-6060-90ZERO1/4 WIND STRENGTH1/2 WIND STRENGTH3/4 WINDSTRENGHTFULL WIND STRENGTHThis is somewhat easier & and definitely quicker
24 Shallow FogAs fog starts to form in the early evening, there is often a shallow layer, a few feet thick, next to the ground.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 light will no longer be visible.A pilot in the circuit, especially at night may not even notice this as the ground & lights are clearly visible
25 Shallow FogThis slant visibility can be measured & if the runway visual range ( RVR ) is under 800 metres a safe landing is unlikely.UNDER 800 METRES? ABORT!
26 It causes the following problems: PrecipitationIt causes the following problems:This is a fancy word for rain! Covers rain, sleet, snow, hail etcLeaks into aircraft on the groundOnce a fluid has frozen on the airframe it must be removed with de icing fluidFloods runwaysIf it is frozen it can stick to the airframe and cause takeoff problems
27 Apart from thunderstorms, the main hazard is ice Airborne HazardsApart from thunderstorms, the main hazard is iceEven in VMC icing can form on an airframe at certain temperatures.
28 This can be fatal, but why ? TEMPERATUREICE !This can be fatal, but why ?
29 In a car the main problem on a frosty morning is the frozen windscreen In an aircraft this is easily cured by heating thewindscreen.But you cannot heat the whole of the airframeSo the ice will stick to the surface.
30 On the wings this means the shape of the wing changes & will eventually cease to be an aerofoil Ice on leading edgeWING
31 However this is not all. As the ice gathers on the airframe the weight increases This means that lift will be decreasing, & eventually the aircraft will fly like a brick
32 Icing can also affect other aspects of the aircrafts operations, such as undercarriages, controls surfaces, and radio aerialsIt will also affect engine operation, so the best advice is to stay away from icing
Your consent to our cookies if you continue to use this website.