050 09 00 00 FLIGHT HAZARDS

a. Whenever ground temperatures are at or below 0 °C.
b. Whenever flights take place through cloud or rain at temperatures below 0 °C. The most
severe icing is usually present in the temperature range 0 °C to about -10 °C.
c. At heights where the temperature is between 0 °C and -20 °C, the rate of icing may be
severe over a substantial depth of cloud for a wide range of cloud-base temperatures.
d. At heights where temperatures are between about -20 °C and -40 °C, the chance of moderate or severe icing reduces, except in newly developed convective cloud, but light icing is possible.
e. At temperature below -40 °C the chance of icing is small.

The aircraft provides a freezing nuclei.

Generally warm, humid air, the temperature in the carburettor can be reduced by 25°C

a. In cloud and fog where the relative humidity should be assumed to be 100%.
b. In clear air where cloud or fog may have just dispersed, or just below the top of a haze layer.
c. Just below a cloud base or between cloud layers.
d. In precipitation, especially if persistent.
e. The surface and low-level visibility is poor, especially in early morning and late evening, and particularly near a large body of water.
f. The ground is wet (even with dew) and the wind is light.

 

Supercooled water droplets in rain, drizzle, clouds and fog in temperatures well below 0°C

Liquid water below 0°C, smaller than rain. Exist from 0°C to -40°C. The exist where no freezing nuclei are present possibly when they have all been used up making water droplets. They are unstable and sublimate onto the airframe.)

0°C to -15°C – Large droplets. (0°C to -20°C – large and small can exist [PadPilot])

-15°C to – 45°C – small droplets. (-20°C to -40°C [PadPilot])

>045°C – no supercooled droplets. (Below-40°C [PadPilot])

Cu

• Large droplets – Cu has more vertical support. Large in the lower levels, small in the upper levels.
• Down to -20°C mostly water droplets, below is liquid drops or ice.
• New clouds tent to have more liquid drops.
• Severe icing between 0 °C and -20 °C.
• Icing probability low between -20 °C and -40 °C.
• Due to the cellular nature of Cu, icing risk can be different.
• Always assume severe icing I Cu

 

St and StCu – Small – unlikely to support large droplets.

• Usually only water droplets
• Water down to -15 °C
• Icing risk no worse than moderate down to -15 °C and no worse than light at lower temperatures.
• Shallow clouds so relatively small droplets

 

Alto St and Alto Cu

• Altostatus may extend a long way vertically, larger SCWD.
• 0 °C to -15 °C may produce ice but not common due to water content,
• Orographic lift gives moderate to severe to -20 °C.
• Altocumulus greater vertical extent SCWD to -30 °C, light to moderate icing.

Nimbostratus

• Same as altostratus, but can form lower giving increased droplet concentration and therefore ice severity.
• Moderate icing but orographic lifting can increase this.

Cirus

• Only ice crystals, icing unlikely. possible engine implications.

Hoar – Occurs in clear air on a surface whose temperature is reduced below the frost-point of the air in contact with it. Occurs on clear nights when there is a fall in temperature to a value below 0 °C.

Rime – Occurs when small supercooled water drops freeze on contact with a surface at a temperature below 0 °C. At ground level it forms in freezing fog.

Rime Ice. In flight it may form in clouds of low water content composed of small droplets, comparable with those of freezing fog. Most liable to occur at low temperatures where small, unfrozen cloud droplets freeze almost instantaneously.

Clear Ice – Occurs in dense cloud of convective or orographic type.

A cold soaked wing from a previous flight, including the fuel can cause moisture to sublimate onto the wing when it otherwise wouldn’t.

 

Larger droplets in Cu clouds are more severe. They freeze slower releasing latent heat and spread backwards.

Colder air reduces risk, but freeze more rapidly.

Ice crystals usually means less SCWD and less airframe icing, although ice crystals can still affect engines.

The more SCWD the more icing – obvs.

A faster wing will pick up more ice and a thinner wing will also pick up more, because a thinner wing generally has to travel faster meaning it encounters more droplets. Also the separation point on a thin wing is closer to the leading edge than it is on a thick wing increasing likelihood of contact.

Flying faster increasing kinetic energy can delay icing.

Lots of liquid water releases latent heat giving some resistance to icing HOWEVER this can also increase blowback of the icing.

Liquid water content is the density of water in cloud g/m³. Governs how much water is available for icing.

 

 

Orographic lifting can add energy to the clouds to help support larger SCWDs.

The 0 °C isotherm lowers…

Normally benign St gets a convective component.

Transparent, from large droplets, heavy and hard to remove.

When leading edges are < -0°C.

Large SCWD are required which means this ice can be formed in the lower levels of CU pro Ns that has orographic lift to support vertical movement.

Can occur in freezing rain.

Latent heat released as it freezes, delays further freezing allowing the ice to spread aft.

Transparent, harder and stronger, no air trapped.

Small SCWD. Brittle, fuzzy, that protrudes into the boundary layer.

Small SCWD that freeze immediately with an airframe that is < -0°C , less latent heat. Mostly found at -10°C to -40 °C. Easier to remove. Normally colder higher levels of a cloud where SCWD are small. Can occur in freezing fog or on the windward side of objects.

Trapped air, brittle, easier to remove than clear ice. Droplets freeze instantly so build up forwards into the airflow.

Rime and clear rarely form in isolation. It is a mix of clear and rime.

Needs both large and small SCWD. 0 °C and -20 °C.

Mix of the two. Can form a top and bottom horn of ice mixing the characteristics of the two types.

Can stick to airframes <0 °C. Likely on cold soaked aircraft.

Where water vapour sublimates onto a surface.

In the morning after clear, calm nights in autumn and winter. Can occur in flight when descending into warmer air with a cold soaked airframe or through a warm front.

Brittle but bottom layer may be quite hard to remove.

Not reportable: Trace, Light.

Reportable: Moderate, severe and clear and rime.

Performance, stuck mechanisms, disrupted sensors.

 

Fronts – embedded Cbs along a cold front.

Under a warm front in winter.

In St, moderate rime ice.

Inside Cu  0 °C to -15 °C

 

Use charts at all levels and sigmets.

Fly in clear air or descent into warm, climb into very cold air.

 

Occurs in convective weather, high up. 

Above mesoscale convective stuff.

Occurs in very active humid  convective systems.

Engine roll back and sensor blockage.

Avoid flying over or just downwind

Light – Slight, erratic changes. IAS ±5-15 kt. <0.5g

Moderate – IAS ±15-25 kt. 0.5-1g

Servere IAS ±>25 kt. >1g

Disruption of flight path

Sig weather charts and sigmets.

Low altitudes, avoid the friction layer, fly higher and upwind of mountains.

 

 

Turbulence – Disturbed air and generally affects an aircrafts attitude not altitude although will do indirectly of course.

Wind shear – Much more serious, substantial changes in wind velocity in the vertical or horizontal plane.

Gust, when there is a temporary change in mean wind speed >10 kt.

Yep…

Violent buffeting of aircraft.

 

Variations in wind vector along the flight path.

Vertical – change of horizontal wind vector with height.

Horizontal – Change of wind vector with horizontal distance.

Around the take off and final approach paths.

Especially at a cold front.

Thunderstorms – macro and microbursts

Fronts – large temperature differences and when they are moving at least 30 kt.

Inversions…

Surface friction or large buildings in the way.

Increase/reduction in air speed = dangerous when close to the ground obvs….

Charts.

Strong, curved jet streams, thunderstorms and mountains.

Cumulonimbus ! Possibly altocumulus castellANUS

Air Mass – Land base, summer Ts generated by surface heating in the unstable air behind cold fronts.

Frontal Ts – Unstable warm fronts and moist cold fronts, similar to squall lines.

Squall lines – A line of intense Ts stretching for miles.

Supercells – Large and severe with a mesocyclone. Powerful up draughts help them stay alive longer, can produce tornados and large hail etc.

Orographic – Formed by mountains. Unstable air and upslopes produce Ts on the windward side of the mountain.

Developing – Up draughts – 15 – 30 minutess

Mature – Rain. Up and down draughts 15 – 30 minutes.

Dissipating – Predominantly down draughts. 1.5 – 2.5 hours.

 

1 – 3 hours total.

 

Initial – Great depth of instability
• Strong vertical windshear
• Stable layer between warm (lower) and cool (upper) air which is eventually broken down
by insolation.

Supercell – Very strong up and downdraughts produced in the one large (super) cell give rise to
violent weather and even tornadoes (an average of 33 tornadoes per year have occurred in Britain over recent years reminding us that they are not a phenomena restricted to the USA.)
• The mature stage may last several hours.

All the bad stuff: Lightning, hail, heavy precipitation, turbulence, wind shear, icing – the bloody lot.

No…

The air above is positively charged and the surface is negative. Lightning zaps the Earth with negative charge…

ground stroke – Typical lightning strike to the ground

intra-cloud lightning – with a single thundercloud.

cloud-to-cloud lightning – between two different cells.

upward lightning – Uncommon but can happen

A build up of static at the edge of the windscreen.

Rising ice crystals collide with graupel (crusty snow), They become positively charged as the graupel becomes negatively charged at the bottom. When a high enough potential difference exists BOOOM!

Can puncture the structure and mess about with compasses but generally lightening goes through on its way to the ground.

Strong down moving air that diverges and curls backwards, severe winds.

Micro – small scale 4km across for 5 mins. Macro are larger 4km across and last about 20 mins.

The mass that the up draught has been suspending collapses dragging air with it, some rain evaporates cooling the air and making it more dense.

Above

Above

Severe turbulence with positive and negative wind shear.

Yep, done that then…

Common sense really. Checklist…. sensors may give erroneous readings, it will be bumpy.

Don’t fly above it.

Rotating column of air touching the ground somewhere near a Cu cloud.

From supercells involving vertical wind shear. The air is lifted and tightened by convection.

<100 kt rotational speed.

80 m diameter.

Last a few miles.

Spring and early summer.

Big in the US (150m diameter)

 

1200 per year in the States.

A weak tornado that picks up dust.

 

Wind shear is associated with a strong surface inversion. Turbulences when flying through an inversion.

It is stable and uniform with no convection or weather, certainly in the lower levels. Sometimes mega storms can get up there though…. Cold and dry.

I don’t know what this is asking. I suppose it is the inversion that caps the weather.

They can intensify, weaken, accelerate or decelerate fronts, basically aids or hinders convection…

Mountain waves as discussed earlier.

No..

Increased vertical support that can hold larger droplets, especially as St clouds become able to hold the large droplets usually associated with clear ice and Cu clouds.

At night, cold air sinks as discussed before.

Turbulent mixing due to the terrain brings cooler air from aloft and hence forms an inversion.

Poor visibility due to lack of convection. Smooth flying conditions.

A physical barrier that restricts the ability to see through it ! There are a greater number of droplets in drizzle than rain.

Drizzle <500m

Snow <50m

Fog <1000m

Mist 1000-5000m

Haze, smoke, volcanic ash, sand and dust. <5000m

Above..

More or less than ground visibility.

Fog and mist, the airfield may be visible form overhead but not from a slant range…because it’s further away from that angle.

Above or below the layer of haze/fog brings better visibility.

DR Low drifting = dust, sand or snow has been raised <2m

BL >2m

Above

Particles lifted by strong and turbulent wind. Dust gets higher than sand.

Well, that’s bloody obvious…

Especially when pollution, haze or mist are present.

Can give adverse depth perception.