Met 2 Flashcards
What are the effects of icing on an aeroplane?
Aerodynamics Weight Engine blockage Undercarriage jammed Control surfaces jammed Pitot tubes blockage Communications aerial icing Vision -canopy icing Vibration
What factors affect the severity of icing?
Cloud droplet variables: - size (larger droplet, more severe icing) - concentration - temperature Aircraft varaibles: - Shape (more streamlined, more icing) - Speed (higher speed, more icing)
What situation causes most icing on aircraft?
When a sub-zero aircraft strikes super-cooled water droplets.
In what temperature range is icing most common?
-15 to 0 degrees C more super cooled droplets close to zero
What are the two types of icing in cloud?
Clear Ice Rime Ice
Describe clear ice
1) Clear 2) Dense 3) Adhesive 4) large super cooled droplets 5) temps close to zero 6) slow freezing
Describe rime ice
1) White 2) Low density 3) Brittle 4) small super cooled droplets 5) very low temps 6) rapid freezing traps air
Other forms of icing (not incl rime and clear ice)?
1) Packed snow 2) Rain ice 3) Hoar frost 4) Engine ice
What are the 2 ways that kinetic heating occurs?
1) Increased pressure at LE 2) Friction between aircraft skin and atmosphere
Give 1 advantage and 1 disadvantage of kinetic heating
Advantage: Raises temp above 0 degrees = no icing Disadvantage: Raises temp from very cold to close to 0 degrees = more severe icing
How long does it take for 0.5cm of ice to build up in light, moderate and severe icing conditions?
Light = 15-60mins Moderate = 5-15mins Severe = <5mins
What are the conditions for a thunderstorm?
1) Deep untable layer - preferably unstable up to tropopause 2) Trigger action - heating, mountains, fronts 3) High moisture content - high dew point
What two weather conditions are assumed to occur in CB?
Sever icing and moderate turbulence
What are the hazards associated with thunderstorms?
WHISTLER Weather - heavy precip Hail severe Icing Squall/strong winds severe Turbulence Lightning severe Electrical/magnetic effects Rapid pressure changes
What are the common indicators of thunderstorm activity?
Cloud type - convective (towering CU, CB, Castellanus, Mammatus) Hail or Heavy precepitation Lightning Radio Crackle Radar returns/echos St Elmos Fire across canopy
What is Meteorological visibility?
The greatest horizontal distance at which known objects can be seen and recognised by an observer on the ground with normal eyesight and under conditions of normal daylight illumination.
What is Prevailing visibility?
The visibility value, as per met vis, which is reached or exceeded within at least half the horizon circle or within at least half of the surface of the airfield.
What is the Runway Visual Range (RVR)?
The maximum distance in the direction of take-off or landing at which the runway, or lights delineating the runway, can be seen from a height corresponding to the average eye-level of the pilot at touchdown.
How is RVR measured?
By an observer (or automatically) from a 15ft high tower near to the runway.
When is RVR to be reported?
Whenever the reported Met visibility is less than 1500m
Why does airborne/slant visibility differ from Met visbility?
When below the haze top the effect of height reduces the visibility below met vis. When above the haze top the slant visibility is greater than met vis.
Define Mist
Visibility reduced by the presence of water droplets in the atmosphere Limits for aviation purposes: 1000m or more (RH 95% or more)
Define Haze
Visibility reduced by solid particles in the atmosphere. Limits: gernerally less than 10km vis
Define Fog
Vsibility reduced by the presence of water droplets in the atmosphere. Limits for aviation purposes: less than 1000m
What conditions generate radiation fog?
Clear skies Light winds Moist air Long cooling period Low-lying ground
What causes radiation fog dispersal?
1) Heating 2) Increased wind (may produce stratus) 3) Change of air mass (drier air)
What conditions generate advection fog?
Warm Moist air Cold surface (land/sea) Wind
What causes advection fog dispersal?
1) Heating 2) Loss of cold surface (eg snow melts) 3) Change of airmass (drier air)
What are the air masses that affect Britain?
1) Tropical Maritime (Tm) 3) Tropical Continental (Tc) 4) Polar Continental (Pc) 5) Polar Maritime (Pm) Returning Polar Maritime Arctic Maritime
Describe the characteristics and weather associated with Polar Maritime:
Cold air over Warm sea - unstable air mass - CU, CB clouds - Showers - Vis good except in showers
Describe the characteristics and weather associated with Tropical Maritime:
Warm air over Cold sea - stable - ST - Drizzle (DZ), mist (BR), fog (FG) - Poor visibility
Describe the characteristics and weather associated with Polar Continental IN WINTER, short sea track:
Cold air over cold land (drier air) - stable - nil cloud - smoke (FU) / haze (HZ)
Describe the characteristics and weather associated with Polar Continental IN SUMMER, short sea track:
Warm air over Warm land (drier air) - slightly unstable - SCT small CU - possible smoke haze - moderate to good visibility
Describe the characteristics and weather associated with Polar Continental IN WINTER, long sea track:
Cold air over Warm sea - unstable - BKN CUCB - snow (SHSN) or rain showers (SHRA) - good except in showers
Describe the characteristics and weather associated with Polar Continental IN SUMMER, long sea track:
Warm air over Cold sea - stable - OVC STSC - DZ, hill or coast fog - moderate to poor visbility
Describe the characteristics and weather associated with Tropical Continental IN SUMMER:
Hot air over a Warm land - stable - nil cloud - possible HZ - good to moderate visibily
Describe the characteristics and weather associated with Returning Polar Maritime:
Cold air over Warm sea ===> Warmer air over Cooler sea - stable - OVC ST SC - DZ, hill or coast fog - poor visibility
What is the difference between warm and cold fronts?
Warm front: warm air replaces cold Cold front: cold air replaces warm
Describe the weather associated with a cold front
Describe the weather associated with a warm front
Draw a warm sector depression
Explain the formation of an occluded front
1) Cold fronts move faster than warm fronts 2) Eventually the cold front catches up with the warm front and occlusion begins 3) Air in the warm sector is pushed up as it is less dense
What are the two types of occluded front?
Cold Occlusion - most common Warm Occlusion
Draw a cold occlusion
Draw a warm occlusion
Why does wind speed generally increase with height? especially near fronts?
As pressure gradient force increases, so does wind speed. The PGF increases with height.
What are the characteristics of the Polar Jet Stream?
Latitude 40-70 degrees N Season - all year Height 30,000 - 35,000ft Direction 200-340 degrees Speed 100-200kts non continuous around the globe
Where are the likely areas for CAT (clear air turbulence)?
1) Near jet streams, especially on the cold side (more tightly spaced contours) 2) Sharply curved contours i.e. large change in wind direction and speed 3) Up to 20nm from and about 5000ft above top of CB 4) High ground (especially where mountain waves are present)
