AV22: Visibility and Icing - HS Flashcards
Visibility
The maximum distance at which we can see and identify an object of suitable dimensions. Used to describe the transparency of the atmosphere.
Prevailing visibility
The maximum visibility at eye level common to at least half of the horizon circle. Also referred to as horizontal visibility.
Tower visibility
The maximum distance at which an object of suitable dimensions can be seen and identified at the level of the tower cab.
Vertical visibility
The distance one can see vertically into a surface based layer.
Flight visibility
The average distance one can see forward from an AC in flight.
Slant visibility
The farthest point on the ground one can see from an AC in flight.
RVR
Runway Visual Range: The computed maximum visibility along the runway at cockpit level.
How does stability of the air affect visibility?
Almost all restricting phenomena are more pronounced in stable air.
Why does stable air make for lower visibility?
- Impurities are trapped in the lower layers
- Continuous precipitation from layer clouds reduce visibility
- Favourable for drizzle and fog
- Particles are not lifted above eye level (drifting phenomena)
How can unstable air make for lower visibility?
- Showery precipitation
- BLSA, BLSN, BLDU
Cause of smoke
Industrial centres or forest fires
Stability of air when smoke is reducing visibility
Stable
Dissipation factors for smoke
- Changing of air mass
- Change of wind direction
- Increase in wind speed
Cause of haze
General pollution
Stability of air when haze is reducing visibility
Stable warm air mass
Dissipation factors for haze
- Changing of air mass
- Change of wind direction
- Increase in wind speed
Cause of BLSN, BLSA, BLDU
Windy conditions
Stability of air when BLSN is reducing visibility
Unstable
Dissipations factors for BSLN
Decrease in wind speed
Cause of radiation fog
Night time cooling
Stability of air when radiation fog is reducing visibility
Stable
Dissipation factors for radiation fog
- Daytime heating
- Increase in windspeed
Cause of advection fog
Advected warm air over cool water or land
Stability of air when advection fog is reducing visibility
Stable
Dissipation factors for advection fog
- Change in wind direction
- Strong winds
- Daytime heating (when over land)
Cause of upslope fog
Orographic lift (adiabatic cooling)
Stability of air when upslope fog is reducing visibility
Stable
Dissipation factors for upslope fog
- Change of wind direction
- Strong winds
Cause of frontal fog
Frontal precipitation (evaporation of precipitation)
Stability of air when frontal fog is reducing visibility
Stable
Dissipitation factors for frontal fog
Passing of the front