Visibility

Question 1

VFR minimum conditions?

Answer 1

Visibility greater than 5km
Vertical cloud distance 1000ft
Horizontal cloud distance 1.5km

Question 2

4 non-atmospheric causes of low visibility

Answer 2

1. Glare from the sun or a windscreen
2. Contaminated windscreens
3. Scratched windscreens
4. UV damaged (acrylic) windscreens

Question 3

5 atmospheric causes of low visibility

Answer 3

1. Water droplets
2. Ice crystals
3. Smoke
4. Chemical pollutants
5. Volcanic ash

Question 4

What visibility does fog imply?

Answer 4

Less than 1000m

Question 5

What visibility does mist/haze/smoke/dust/sand imply?

Answer 5

1000m - 5000m

Question 6

5 types of fog?

Answer 6

1. Radiation fog
2. Advection fog
3. Evaporation/steam fog/artic smoke
4. Frontal fog
5. Hill/upslope fog

Question 7

What are the ideal conditions for radiation fog?

Answer 7

High RH, light winds (2-8kt), clear skies
High pressure system over land
Nighttime temperature inversion

Question 8

3 ways radiation fog disperses

Answer 8

1. Temperature increases above dew point
2. Wind mixing dry and saturated air
3. May lift into a low St or Sc

Question 9

What causes advection fog?

Answer 9

When a parcel of warm, moist air moves horizontally over a colder surface

Question 10

What type of areas in advection fog associated with?

Answer 10

Cool sea areas adjacent to coasts in the summer

Question 11

What causes Steam Fog/Arctic Fog/Sea Smoke?

Answer 11

Very cold air sitting over a warm, moist surface

As soon as water evaporates it condenses causing fog

Question 12

What causes frontal fog?

Answer 12

Rain forces the cloud base down

Warm front over a cold front creates an inversion

Question 13

What causes orographic/hill fog?

Answer 13

Air forced up a slope condenses and forms clouds, close to the surface these are fog

Question 14

What is freezing fog?

Answer 14

Fog at a temperature below 0 degrees

Question 15

What does freezing fog contain?

Answer 15

Supercooled water droplets which freeze on impact

Question 16

What is fog below 2m depth?

Answer 16

Mist

Question 17

What is the weather abbreviation for patchy fog?

Answer 17

BCFG

Question 18

What is the weather abbreviation for partial fog?

Answer 18

PRFG

Question 19

What is the visibility in cirriform clouds?

Answer 19

1000m+

Question 20

What is the visibility in Ac and As?

Answer 20

20 - 1000m

Question 21

What is the visibility in Ns and Cb?

Answer 21

10 - 20m

Question 22

What is the visibility in Sc and St?

Answer 22

10 -30m

Question 23

What is the visibility in Cu?

Answer 23

Less than 20m

Question 24

What is smoke?

Answer 24

Suspension of small particles produced by combustion

Question 25

What is haze?

Answer 25

Suspension of extremely small, dry particles invisible to naked eye and sufficiently numerous to give the air opalescent appearance

Question 26

What is dust haze?

Answer 26

Suspension of dust or small sand particles, raise from the ground prior to the time of observation

Question 27

What wind speed do sand and dust storms require?

Answer 27

15kt+

Question 28

How high can sand and dust storms reach?

Answer 28

Dust storms - 15000ft | Sand storms - few hundred metres (heavier)

Question 29

Visibility in a heavy dust storm?

Answer 29

Less than 200m

Question 30

What happens to air-to-ground visibility when there is fog?

Answer 30

Reduces as you descend

Question 31

VFR operating minima on the ground?

Answer 31

Cloud ceiling greater than 450m/1500ft | Ground visibility greater than 5km

Question 32

How does a control tower report visibility observed?

Answer 32

Whatever it is for at least half of the horizon

Question 33

For visibility reporting what are the different increments?

Answer 33

0 - 800m = 50m increments 800m - 5km = 100m increments 5km - 10km = 1km increments 10km+ = 10km increments

Question 34

What does the USA use for reporting visibility?

Answer 34

Statute miles

Question 35

What is the runwa visual range (RVR)?

Answer 35

The range over which the pilot of an aircraft on the centreline of a runway can see the runway surface/edge lights/centreline lights

Question 36

Where are RVR detectors placed?

Answer 36

2.5m above the runway within 120m | Usually threshold, mid point and stop-end point

Question 37

When is RVR reported?

Answer 37

When RVR is below 1500m

Question 38

What do U, D and N indicate when reporting RVR?

Answer 38

U - upward visibility trend D - downward visibility trend N - neutral trend

Question 39

What is the ceiling also known as?

Answer 39

Vertical visibility (VV)