Lesson Seven: Navigation II and Meteorology I

Don’t read:
Air Nav: You should read everything else in the rest of this chapter, although the focus will be on what I’ve taught here.

Units
Statute mile (sm) = 5280’
Nautical mile (nm) = 6080’
Kilometer (km) = 1000 m
Knot = 1 nm / hour
Groundspeed = Distance flown / time
Aeronautical charts
Earth is a sphere, although we can’t bring a globe with us to navigate everywhere we go
Need to project Earth’s round surface into a plane
Four basic elements in map construction
Areas
Shapes
Bearings
Distances
Depending on purpose, one or more of these elements is preserved as best as possible, although there will inevitably be some distortion in others.
Mathematical bases for which maps are constructed called projections
Lambert Conformal Conic
Wrap a cone around the part of the Earth you want to make a map out of. If the Earth was covered with paint, the image that you would get on your piece of paper would follow LCC projection.
Angles between meridians and parallels will be the same on the chart as they are on the ground.
Properties
Meridians are curves or straight lines converging towards the pole. Curves generally inappreciable.
Parallels of latitude are curves which are concave towards the nearest pole. Concavity usually appreciable.
Constant scale across map sheet, across all meridians and parallels.
A straight line drawn between any two points is an arc of a great circle.
The VFR Navigation Charts (VNC) and the World Aeronautical Charts (WAC) are based on the LCC projection.

Mercator
Wrap a cylinder around the Earth so that the cylinder would fit snugly in contact with the Earth’s equator (tangent at the equator)
Properties
Meridians are straight and parallel lines.
Parallels are straight and parallel lines.
A straight line between any two points is a rhumb line.
No constant scale of distant; heavy distortion at high latitudes.
Transverse Mercator
Variant of the Mercator, where the cylinder is rotated 90o such that the points of tangency are along a meridian (with a pole on either side)
Chart is then accurate along the selected meridian.
Accurate in depicting scale, esp. in small geographic areas.
Used on the VFR Terminal Area Charts (VTA)

Types of aeronautical charts
VNC
LCC projection
Used for visual navigation at lower altitudes and slower speeds.
Covers a fair swath of land, with moderate detail resolution.
Northern half of coverage on one side, southern half on the other.
Each chart identified by the name of principal landmark on the chart (typically a major city)
Scale – 1:500,000
WAC
LCC projection
Designed for visual nav at higher altitudes and faster speeds.
Covers a large land area, with low resolution.
18 charts cover the whole country.
Scale—1:1,000,000

VTA
Transverse Mercator
Published for airports where there is large airplane traffic, and which there is a mix of controlled airspace
Scale: 1:250,000

Read section on Canada Flight Supplement
Further definitions
Required track:Proposed path of airplane over ground.
Track made good: Actual path of airplane over ground.
Track error: Angle between required track and track made good, measured in degrees left or right of required track.
Opening angle: Angle between the required track and the track made good.
Closing angle: Angle between the old required track and the new required track necessary to arrive at the destination.
One-in-sixty rule: An error in track of one degree will cause an error in position of about one mile in a distance of 60 miles.
(Angle off track)/60 = (Miles off track) / (Miles travelled)
Could also use trig ratios to solve, not sure if you’ll have access to a calculator during the exam (you should though)

The Atmosphere
78% nitrogen, 21% oxygen, 1% everything else
Of that “everything else”, the most important is water vapour in terms of weather; can only be found in lower levels of the atmosphere
Atmosphere has weight, which gives rise to pressure: P = F/A
Properties: mobility, capacity for expansion, capacity for compression
Air can rise (and cool), air can descend (and warm), air can move horizontally (advection)
Troposphere
Lowest layer of the atmosphere, where all of the weather happens
Surface – 28000’ (at the poles) to 54000’ (at the equator)
Within this layer, pressure, density and temperature decrease with altitude.
Top layer of troposphere called tropopause
Stratosphere
Layer roughly 50000’ from the tropopause
Temperature increases with altitude to roughly 0oC at the stratopause
Little water vapour here; some thunderstorm tops may punch through
Mesosphere
Thermosphere
Exosphere
**International Civil Aviation Organization (ICAO) Standard Atmosphere (ISA)
Air is a perfectly dry gas
MSL pressure of 29.92’’ Hg (1013.25 hPa)
MSL temperature of 15oC
Rate of temperature decrease (lapse rate) is 1.98oC/1000’

Clouds
Condensation of the air, resulting in visible water droplets forming aloft
Occurs when a parcel of air becomes saturated (i.e. temperature = dew point)
Identified based on altitude of formation as well as how they form
High (16500’ – 45000’), Middle (6500’ – 23000’), and Low (SFC – 6500’)
Cumulus (cumuliform clouds)
Form in rising air currents, evidence of unstable conditions
Stratus (stratiform clouds)
Form in horizontal layers, evidence of stable conditions
Clouds with precipitation typically modified with nimbus
High clouds
Composed of ice crystals
Cirrus (CI): Very high, thin and wispy. Fair weather, but could indicate approaching warm front.
Cirrocumulus (Cc): Thin sheets of cotton-ball like clouds, often called mackerel sky. Little indication of future weather.
Cirrostratus (Cs): Very thin high sheet of cloud which could produce a halo effect. Indicative of incoming warm front
Middle clouds
Mix ice crystals and water vapour
Altocumulus (Ac): A layer or series of rounded masses, sometimes indicates approaching front, but most often indicate very little.
Altocumulus castellanus (Acc): “Turreted” Ac, indicate instability and turbulence. May develop into thunderstorms
Altostratus (As): Thick veil of cloud covering the entire sky; light from sun may shine through just a bit. Indicates approaching warm front. Icing may occur in this cloud, as well as trace precipitation.
Low clouds
Composed of water droplets, although they may be supercooled
Stratus (St): Uniform layer of cloud, thick and blocks out sun’s light. When stratus is broken up by wind, called stratus fractus
Stratocumulus (Sc): Layers or patches of large rounded masses/rolls of cloud. Some blue sky in between. May have some precip.
Nimbostratus (Ns): Low layer of uniform, featureless cloud. Produces drizzles
Vertical development
Cloud bases as low as 1500’, can climb to above tropopause
Mix of water vapour, supercooled and ice crystals
Instability and turbulence present
Cumulus (Cu): Dense clouds of vertical development.
Towering cumulus (TCu): Cumulus clouds built up into high heaps, baby stage of thunderstorms.
Cumulonimbus (Cb): Thunderstorms! Precipitation, heavy turbulence, lightning, and potentially tornadoes.

Sky condition
Oktas = eighths of sky covered by cloud
Clear (0 oktas)
Few (1-2 oktas)
Scattered (3-4 oktas)
======CEILING EXISTS======
Broken (5-7 oktas)
Overcast (8 oktas)
Cloud formation
Water vapour  Droplets = condensation
Occurs when the relative humidity is high and when condensation nuclei are present in the air and when there is cooling of the air
Level at which WV condenses called condensation level
Clouds which form at temperatures well below freezing would likely form by deposition (WV  Ice particles)
Formed one of two ways:
Air, in which WV is present, is cooled to its saturation point
Relatively drier air, at lower temperatures, has WV added to it to bring it to its saturation point
Most common is cloud formation by adiabatic expansion due to rising air
Lifting processes
Orographic lift
Lifting by air blowing against the side of a mountain and being forced up
Large banks of cloud (with precip) generally form on windward side, drier conditions on leeward side
Convection
Warm air rises; heating of ground by the sun causes air to warm
Also occurs when air moves over a surface that is warmer than itself; air is heated by advection and convective currents develop
Frontal lift
Warm air advancing on cold air mass, warm air rises over cold air in long gradual slope
Cold air advancing on warm air, cold air pushes warm air up in sharp slope
Turbulence
When strong wind blows over rough surface, friction between ground and air cause eddies which force air up
Convergence
When air piles up at the center of a low pressure system, air has nowhere to go but up

Pressure
P = F/A; the more air is on top, the higher the pressure
Measured using a mercury barometer, where the air pressure pushes on a plate of mercury, forcing up through a hollow tube
Station pressure is the true atmospheric pressure at a weather station
MSL pressure is the station pressure + the weight of an imaginary column of air extending to sea level
Calculated using averaged temperatures over the past 12 hr.
Altimeter setting is like MSL pressure except it’s calculated based on the ICAO standard atmosphere
Pressure systems
Areas of like pressure are drawn on weather maps as isobars
Low pressure areas or cyclones are regions of relatively low pressure with the lowest pressure at the center
A tornado is an example of a very deep, small but concentrated low
Deepness of a low depends on how low the center is relative to its surroundings
Generally move in the easterly direction
Typically associated with poor weather
Secondary lows are smaller distances of a cyclonic nature forming within the area dominated by the main depression; revolves around the low in a ccw direction
Troughs extensions of lows, with higher pressure on either side of the extension.
Col is a neutral region between two highs and two lows
Conditions tend to be unsettled
High pressure areas or anti-cyclones are areas of relatively high pressure
Weather accompanying it is usually fine or fair
Generally moves slower than lows
Ridges are extensions of highs, with lower pressure on either side of the extension.
Pressure changes
Pressure readings are taken at regular intervals (hourly) at weather stations
Weather maps prepared four times a day every six hours
Pattern of changing pressure called pressure tendency
Pressure gradient
Air moves from areas of high pressure to low pressure
Pressure gradient refers to the horizontal change in pressure
Speed at which movement of air occurs depends on the gradient; the steeper the gradient, the stronger the winds
Imagine that a ball is a parcel of air, and that it’s resting on the ramp. If the ramp has a greater incline (i.e. a greater gradient), then the ball would roll down faster!
Gradient is typically steeper around a low than around a high
Can be measured by how close the isobars are to each other
**Coriolis force
Air does NOT move directly from highs to lows in a straight line!
The Earth is rotating, and because of its rotation a “force” is exerted on moving particles – force called Coriolis force

Red: Direction you think you’re going

Green: Where you end up

In the Northern Hemisphere, the CF deflects moving things to the right; opposite in the SH
Causes winds to blow ccw around a low and cw around a high in the NH
Buys Ballot’s Law: If you stand with your back to the wind, the low pressure area will be on your left.

Surface friction and centrifugal force also has an effect on the winds. Surface friction in particular causes the winds to come in at an angle to the centers of lows; come out an angle at the centers of highs.
Aloft, where surface friction is negligible, the winds flow around the pressure systems without coming in or going out
Convergence and Divergence
At the surface, where air comes into the centers of lows, they have nowhere to go but up; results in convergence
Where there is a high pressure system, air flows out; needs air to replace center, so the air comes from above. Air flowing out results in divergence

Winds
Defined as the movement of air, typically caused by pressure gradients
Important for pilots (duh!)
Read Hemispheric Prevailing Winds and Upper Level Winds
Surface winds
Affected by surface friction
At 3000’ AGL, the wind generally blows parallel to the isobars with a speed proportional to the pressure gradient
Land and sea breezes
Caused by differences in temperature between the sea and the land; diurnal (day-night cycle) variations
During the day, the ground heats up faster than the water; warm air rises, and so air goes from the water to the land (sea breeze). The air aloft then fills in the void over the water by descending over the water.
During the night, the water cools down slower than the land; air at the surface goes from land to water (land breeze)
Mountain winds
During the day, the sun warms up the slope of a mountain
Air rushes up the mountain (anabatic wind/valley breeze)
During the night, the slopes cool by radiation
Air rushes down the mountain (katabatic wind/mountain breeze)
Mountain waves
Air flowing over ranges usually rises relatively smoothly up the slope, but can pour down the other side with great force and oscillate
Buoyancy of air counters gravity
If air mass has high moisture content, cool clouds would form
Cap cloud
Orographic lift causes cloud to form on ridge, and looks like a hat lying on top of mountain.
Lenticular clouds
UFOs forming at the crests of the mountain wave
May extend well above 40000’

Rotor clouds
Form in rolling eddies downstream
Resemble long line of Sc clouds; can develop into thunderstorms
Dangers
Vertical currents
Downdrafts of 2000’/min. to 5000’/min.
Turbulence
Usually found at top of rotor clouds
Wind shear
Wind speed varies dramatically between crests and troughs of waves
Altimeter error
Increase in wind speed results in an accompanying decrease in pressure
Icing

Gust
Sudden rapid and irregular fluctuation in the upward/downward movement of air currents
Caused by mechanical turbulence that results from friction between the air and the ground
Squall
Sudden increase in the strength of the wind of longer duration than a gust
May be caused by the passage of a fast moving cold front or TS
Read Diurnal Variations
Eddies
Friction between moving air and surface can produce swirling vortices of air
Vary in size and intensity
Encountered during T/O and landings
Dust Devils
“Tiny tornadoes” that occur frequently on the hot dry plains of North America
Pose the greatest hazard near the ground where they are most violent
Tornadoes
Violent, circular whirlpools of air associated with supercell thunderstorm
Range in diameter from about 100’ to one half mile
Wind speeds up to 300 kts
Wind Speed and Direction
Expressed in knots and degrees FROM where the winds are coming
In aviation reports, they are always reported in degrees true
In ATIS broadcasts and in the info given by the tower for landing and T/O, reported in degrees magnetic
“If read, true. If heard, magnetic.”
Veering and Backing
Veering occurs when wind changes direction cw
Backing occurs when wind changes direction ccw
In a descent from several thousand feet to ground level, the wind will usually back and decrease in intensity due to surface friction as well as imbalancing of forces
Wind shear
Sudden tearing effect encountered along the edge of a zone in which there is a violent change in wind speed or direction
Dangerous because the change in wind speed can be more than what the plane or pilot can handle (huge accelerations/decelerations)
Vertical wind shear most common near the ground, and can be dangerous during T/O and landing
Low speeds, low altitudes + sudden drop in airspeed due to wind shear  unrecoverable stall
Read the rest of the section on Wind Shear, The Jet Stream and Clear Air Turbulence