Visibility Flashcards
What does visibility mean?
A) greatest distance a black object of suitable dimensions (situated near the ground) can be seen and recognised when observed against a bright background.
B) Greatest distance at which lights in the vicinity of 1,000 candelas can be seen and identified against a unlit back ground.
List the intervals that
Visibility is reported
- Less than 500m 50m intervals
- 500-5,000m -100m intervals
- 5km-30km - 1KM intervals
- 30km-70km - 5km intervals
-thereafter reported as greater than 70km
Reduction is vis below 5000m has to be reported.
True
Define Fog
A suspension of small water droplets reducing visibility below 1,000m
Define Mist
A suspension of small water droplets visibility is not less than 1,000m
Define haze
A suspension of solid particles of smoke or dust reducing visibility to not less than 1,000m where the relative humidity is less than 95%
Define Runway Visual Range (RVR)
Indicates the range over which the pilot of an aircraft on the centreline of a runway can expect to seethe runway surface markings, lights, delineating the runway/centre line
What are the 2 methods RVR is measured?
Human observer
IRVR
The number of IRVR units is determined by the category of ILS or MLS installation and runway length. True or False?
True
What is oblique visibility?
An approach aircraft looking obliquely through layer of mist or fog.
When the sky is obscured by fog/ falling or blowing snow “VV//“ is reported in lieu of cloud information.
True or False?
True.
What is prevailing visibility?
The greatest visibility value which is reached within at least half of the horizon circle/ within half the surface of the AD.
How is prevailing visibility done?
By mentally dividing the horizon circle into as many segments of equal visibility as needed to measure the differing visibility.
The lowest visibility is also reported in the METAR when it is less than 1500m or less than 50% of the prevailing visibility, along with its general direction.
True
When does radiation fog normally occur?
During autumn n spring
How is radiation fog formed?
On a clear night the ground radiates heat and it’s temperature drops. If the Air is sufficiently moist the layer in contact with the ground will be cooled below it’s dew point and condensation will occur.
What wind speed is needed for radiation fog?
2-8kts
List the 5 requirements for fog
To form.
1) Clear Sky- Earth radiates heat
2) land surface - rapidly cools and conduct cooling to adjacent air
3) Moist Air - layer contacting ground will reach its dew point
4) light wind - 2-8kts
5) Long night- maximum time for effect to be established
Radiation fog often forms in low laying marshy ground, not high ground.
True
Describe advection fog
Warm air with high humidity cools enough when in contact with a cold surface to cause condensation.
Is wind speed a critical factor for advection fog?
No.
What is steam fog?
Caused by cold dry air moving over a relatively warm water. Small quantities of the water evaporates into air and cause localised condensation that resembles steam.
What is smoke pollution?
In light winds and a temperature inversion, the atmosphere becomes very stable and traps smoke and industrial pollutants
What is required for smoke pollution to move on?
A change of air mass to unstable conditions
