Hazards

Question 1

What is wind shear defined as?

Answer 1

Change in wind velocity

Question 2

What is a low-level jet?

Answer 2

A fast-moving stream of air at a low level

Question 3

How are low-level jets formed?

Answer 3

Air circulating around a high hits a mountain range and is accelerated into a narrow stream along the range. A surface inversion must be present to shield the flow from the surface friction and allow speed to increase.

Question 4

When are maximum wind speeds usually encountered with low-level jet streams?

Answer 4

Early morning (Pre-dawn) when the surface inversion is strongest

Question 5

What is turbulence defined as?

Answer 5

Vertical wind shear

Question 6

What is convective turbulence caused by?

Answer 6

Rising air currents such as found in and below cumulus and cumulonimbus cloud

Question 7

Where is turbulence most severe in cumulonimbus cloud?

Answer 7

Where the boundary between up and down draughts produces strong vertical wind shear

Question 8

How is mechanical turbulence generated?

Answer 8

Wind blowing over and around surface obstructions

Question 9

What does the severity of mechanical turbulence depend on?

Answer 9

• Wind speed
• Height of obstructions
• Surface roughness
• Stability of atmosphere

Question 10

In regards to mechanical turbulence; what will stable conditions result in?

Answer 10

Considerable lee-side turbulence

Question 11

Lee turbulence may be less if….

Answer 11

There are unstable conditions as rising airlifts the turbulent air

Question 12

Where is the worst turbulence in mountain waves?

Answer 12

In the rotor zone beneath the wave crests

Question 13

What is frontal turbulence?

Answer 13

Wind shear at the boundary of two air masses of different temperature

Question 14

What are the 3 types of airframe icing?

Answer 14

• Hoar frost
• Rime ice
• Clear ice

Question 15

What is hoar frost?

Answer 15

A fine light crystalline deposit of ice that forms by deposition when the aircraft skin temperature falls below 0 degrees in high humidity conditions

Question 16

When is a common time for hoar frost to form?

Answer 16

• Overnight on parked aircraft

- Aircraft with below 0 skin flys through warm moist air

Question 17

What is hoar frosts biggest hazard?

Answer 17

It doesn’t add too much weight however it disrupts airflow over the aerofoil surface, reducing aerodynamic efficiency

Question 18

What is Rime ice?

Answer 18

A white opaque rough deposit of ice formed by small supercooled water droplets freezing upon impact with aircraft surface

Question 19

What is the most common temperature range for rime ice?

Answer 19

-10 degrees to -20 degrees

Question 20

What is the cloud type generally associated with rime ice?

Answer 20

Stratiform

Question 21

What is clear ice?

Answer 21

A transparent sheet of ice formed by slow freezing of large supercooled water droplets

Question 22

What is the most common temperature range for clear ice?

Answer 22

0 degrees to -15 degrees

Question 23

Why is clear ice the most dangerous?

Answer 23

It adds considerable weight and seriously reduces the aerodynamic efficiency

Question 24

Where is clear ice encountered?

Answer 24

• The cumuliform cloud above the freezing level
• Also possible in thick altostratus and nimbostratus
• Orographic cloud is also likely to produce clear ice due to the large droplet size

Question 25

When is carburetor ice possible?

Answer 25

Over a wide range of outside air temperatures but humidity must be relatively high

Question 26

What is oblique visibility?

Answer 26

Visibility on a slant

Question 27

What are microbursts?

Answer 27

Strongly concentrated downbursts of air from the base of a convective cloud

Question 28

What are microbursts often associated with?

Answer 28

Squall lines, thunderstorm activity, and virga

Question 29

What is the typical life cycle of a microburst?

Answer 29

15 minutes

Question 30

What happens to an aircraft in a microburst?

Answer 30

The aircraft will initially experience an increasing headwind that will improve performance, followed by a decreasing headwind the down draught and sink followed by an increasing tailwind

Question 31

What is the main concern with a microburst?

Answer 31

The velocity of the downburst will exceed the climb potential of the aircraft