Lesson 12

Question 1

What are the four main causes of turbulence?

Answer 1

• Convective (or thermal currents)
• Mechanical disturbances
• Wind shear
• Wake turbulence

Question 2

Define stable air

Answer 2

Stable air generally means smooth and stable flying conditions since the air will resist upward
or downward displacement. Stable air tends to return to its original horizontal level.

Question 3

Define unstable air

Answer 3

Unstable air is lifted and continues to rise on its own, since the lifted air is buoyant and
becomes warmer and lighter than the surrounding air.

Question 4

Define Dew Point

Answer 4

Dew point is the temperature at which air cooled at constant pressure and without
the addition or removal of water vapour becomes saturated, leading to condensation.

Question 5

What are the signs of stable air?

Answer 5

Stratus-type cloud or fog
* Low visibility when dust, smoke, haze, or fog are present
* Steady precipitation
* Consistent, steady winds
* IFR conditions for ceiling and visibility

Question 6

What are the signs of unstable air?

Answer 6

Cumuliform clouds
* Good visibility
* Gusty wind
* Showery precipitation
* Thunderstorms

Question 7

There are two categories of turbulence. What are they?

Answer 7

Friction turbulence is caused by the
restriction of the movement of the wind.

Thermal turbulence is caused by a rapid
change of temperature in the atmosphere.

Question 8

There are three types of turbulence caused by friction.

Answer 8

• Mechanical turbulence
• Shear turbulence
• Frontal turbulence

Question 9

There are two types of turbulence initiated by heat - What are they?

Answer 9

• Daytime convection turbulence (Unequal heating of the earth’s surface)
• Cold air advection turbulence (Cold air that moves over a warm surface)

Question 10

What is Daytime Convection Turbulence?

Answer 10

Daytime convection turbulence is the result of vertical currents caused by unequal heating of the
Earth’s surface.

Question 11

What is Cold Air Advection Turbulence?

Answer 11

When cold air moves over warmer water or land, heating from below creates unstable
conditions that favour convection currents and turbulence.

The stronger the contrast between the air and surface temperatures, the more heat will be
generated and the stronger the turbulence.

Question 12

Turbulence is classified into three intensities - What are they?

Answer 12

Light turbulence momentarily causes slight, erratic changes in the altitude
and attitude of an aircraft.

Moderate turbulence is a little more intense than light turbulence. Changes
in altitude and attitude occur, but the aircraft remains in control at all times.

Severe turbulence causes large and abrupt changes in aircraft altitude and
attitude as well as large variations in airspeed.
The aircraft may be momentarily out of control.

Question 13

There are 2 classes of downbursts - what are they?

Answer 13

A macroburst is a large downburst with a horizontal diameter of 4 km (2.2 NM) or more when it
reaches the Earth’s surface. It can produce horizontal wind speeds up to 140 knots.
Damaging winds can last from 5 to 20 minutes.

A microburst is a downburst of less than 4 km (2.2 NM) in diameter.
While microbursts are generally of short duration, typically less than five minutes, they can
cause horizontal wind speeds of more than 140 knots at tree top level.

Question 14

What is Virga?

Answer 14

precipitation falling but not reaching the ground

Question 15

What is wind shear

Answer 15

It is characterized as the sudden “tearing” or “shearing” effect encountered along the edge of a
zone in which there is a significant change in wind speed or direction over a short distance.

Question 16

What are the two types of wind shear? what are the two classes?

Answer 16

Directional shear is when two winds blowing from different directions meet
Speed shear is when two winds are close together and blow from the same direction but at different speeds

LLWS - Low level
HLWS - High Level

Question 17

What is Clear Air Turbulence?

Answer 17

CAT is sudden, severe turbulence that occurs without any visual warnings (such as clouds).
Occurs at altitudes of 20,000ft to 40,000ft. It may occur near mountain ranges.
Most of the time it is Jet stream wind shear turbulence.
Most frequently in the winter and less in the summer

Question 18

Describe Low-Level Wind Shear

Answer 18

Low-level wind shear (LLWS) is hazardous because of the proximity of the aircraft to the
ground.

LLWS is characterized by wind direction changes that could go as far as 180 degrees and
speed changes up to 50 knots

It is commonly associated with passing frontal systems, thunderstorms, and temperature
inversions with strong upper-level winds (greater than 25 knots).

Question 19

Pilots have specific procedures for reporting turbulence.
They must report… (5 items)

Answer 19

• Position
• Time
• Altitude
• Type of aircraft
• Type of turbulence (turbulence, chop, CAT) and intensity (light, moderate or severe)

Question 20

What is the difference between chop and turbulence?

Answer 20

Chop causes slight, rapid, rythmic bumps and doesn’t really affect altitude or attitude (light or moderate)
Turbulence will cause changes in altitude or attitude. (light, moderate, severe)

Question 21

How does low level wind shear affect arriving or departing aircrafts?

Answer 21

ARRIVING
A shear perpendicular to the runway could cause an aircraft to drift out of alignment with the runway.
A shear in direction of the runway could put the plane at risk of overshooting the runway or cause a hard landing short of the runway or crash.

DEPARTING
On departure the aircraft could be exposed to a rapid change from headwind to tailwind. The loss of airspeed could be fatal.