Visibility

Question 1

What does visibility mean?

Answer 1

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.

Question 2

List the intervals that

Visibility is reported

Answer 2

• Less than 500m 50m intervals
• 500-5,000m -100m intervals
• 5km-30km - 1KM intervals
• 30km-70km - 5km intervals

-thereafter reported as greater than 70km

Question 3

Reduction is vis below 5000m has to be reported.

Answer 3

True

Question 4

Define Fog

Answer 4

A suspension of small water droplets reducing visibility below 1,000m

Question 5

Define Mist

Answer 5

A suspension of small water droplets visibility is not less than 1,000m

Question 6

Define haze

Answer 6

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%

Question 7

Define Runway Visual Range (RVR)

Answer 7

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

Question 8

What are the 2 methods RVR is measured?

Answer 8

Human observer

IRVR

Question 9

The number of IRVR units is determined by the category of ILS or MLS installation and runway length. True or False?

Answer 9

True

Question 10

What is oblique visibility?

Answer 10

An approach aircraft looking obliquely through layer of mist or fog.

Question 11

When the sky is obscured by fog/ falling or blowing snow “VV//“ is reported in lieu of cloud information.
True or False?

Answer 11

True.

Question 12

What is prevailing visibility?

Answer 12

The greatest visibility value which is reached within at least half of the horizon circle/ within half the surface of the AD.

Question 13

How is prevailing visibility done?

Answer 13

By mentally dividing the horizon circle into as many segments of equal visibility as needed to measure the differing visibility.

Question 14

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.

Answer 14

True

Question 15

When does radiation fog normally occur?

Answer 15

During autumn n spring

Question 16

How is radiation fog formed?

Answer 16

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.

Question 17

What wind speed is needed for radiation fog?

Answer 17

2-8kts

Question 18

List the 5 requirements for fog

To form.

Answer 18

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

Question 19

Radiation fog often forms in low laying marshy ground, not high ground.

Answer 19

True

Question 20

Describe advection fog

Answer 20

Warm air with high humidity cools enough when in contact with a cold surface to cause condensation.

Question 21

Is wind speed a critical factor for advection fog?

Answer 21

No.

Question 22

What is steam fog?

Answer 22

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.

Question 23

What is smoke pollution?

Answer 23

In light winds and a temperature inversion, the atmosphere becomes very stable and traps smoke and industrial pollutants

Question 24

What is required for smoke pollution to move on?

Answer 24

A change of air mass to unstable conditions