C09 - Turbulence and Windshear Flashcards
Define Turbulence?
Sudden changes in wind velocity.
Define Windshear?
Substantial changes in wind velocity both vertical and horizontal.
What affect does Turbulence have on an Aircraft?
The Attitude.
What affect does Windshear have on an Aircraft?
Displace from current flight path.
What are the three intensity terms used to describe Turbulence and their speed in knots?
- Light = 5-15kt.
- Moderate = 15-25kt.
- Severe = >25kt.
During which type of Turbulence are passengers required to wear seat belts?
Moderate and Severe.
During which type of Turbulence can food service no longer be conducted in?
Severe.
Name two types of Turbulence?
- Mechanical.
- Thermal.
What causes Mechanical Turbulence?
Physical obstructions.
What is the Reported Turbulence over the Sea at <15kt, 15-30kt and >30kt (3)?
- Light.
- Moderate.
- Moderate/Severe.
What is the Reported Turbulence over the Plains at <15kt, 15-30kt and >30kt (3)?
- Only Light.
- Moderate.
- Severe.
What is the Reported Turbulence over Broken Terrain at <15kt, 15-30kt and >30kt (3)?
- Light/Moderate.
- Severe.
- Extreme.
What causes Thermal Turbulence?
Air rising due to surface heating.
When is Thermal Turbulence most likely to occur?
During warm days with clear skies.
How are Low-Level Turbulence caused by?
Interactions between Wind and the Earth’s Surface.
What is the name given to the layer which the surface influences the air flow?
Friction Layer.
What type of Airflow is found above the Friction Layer?
Laminar.
What is above the Friction Layer?
Friction Level.
The ‘____’ the Thermal Activity, the ‘____’ the Mechanical Disturbance, the higher the Friction Level (2)?
- Greater.
- Greater.
On a hot day, how high above the surface can the Friction Level be?
1 km / 3,000 ft.
Define Mountain Waves?
Turbulent waves of Air which can form above or downwind of a Mountain Range.
How far can Mountain Waves extend downwind and upwards to the Tropopause?
50-100 NM.
The movement of air in Mountain Waves can exceed ‘____’?
2,000 ft per minute.
Wind Speed at Mountain Height is ‘____’ and increases with Height?
15-20kt.
Wind Direction of Mountain Waves are ‘____’ perpendicular of Mountains?
30°.
In Mountain Waves, a region of ‘____’ can be found at the Mountain Top with less stable air ‘____’ and ‘____’ (3)?
- Stability.
- Above.
- Below.
Where can you find Severe Turbulence in Mountain Waves?
The Rotor Zone.
What visual warning sign can be seen in the Rotor Zone?
Roll Clouds.
Where can you find the most powerful Turbulence in the Rotor Zone?
Beneath the first wave.
Which cloud can act as a visual warning sign to Standing Waves?
Lenticular.
Which type of cloud hugs the side and top of a ridge, to indicate the presences of Standing Waves?
Cap Clouds.
When can Low Altitude Windshear become dangerous in Flight (2)?
- Final Approach.
- Take-off.
How is Vertical Windshear measured?
Knots per 100 ft.
How is Horizontal Windshear measured?
Knots per 1,000 ft.
What speeds can Updraught and Downdraught be found in Thunderstorms?
10,000 ft per minute.
What is the countermeasure against Windshear?
Avoid them completely.
Name four causes of Windshear?
- Thunderstorms.
- Frontal Passage.
- Inversions.
- Topographical.
True or False. Thunderstorms cause the most severe Windshear?
True.
Other than Windshear, what other phenomenon are associated with Thunderstorms (3)?
- Severe Turbulence.
- Lightning.
- Hail.
Define Frontal Passage?
Boundaries between two different Air Mass.
What carries the risk of Windshear in Frontal Passage?
Temperature.
By how much change in Temperature can be associated with Frontal Passage?
> 5°C.
How fast can a Frontal Movement exceed?
> 30kt.
Which type of Front poses more risk?
Cold Front.
Define Inversions?
Can form at Low-Level, especially at night in a High Pressure System.
An Inversion warning is issued if the Temperature changes by more than ‘____’ between ground-level and ‘____’ (2)?
- 10°C.
- 1,000 ft.
Define Topographical Windshear?
Windshear created by natural or artificial features.
True or False. Wind blowing between two buildings, hills and along a valley can change direction and increase speed?
True.
Where can Down Draughts be found?
In, above or below Thunderstorms.
In a Down Draught, currents of Air can change what two factors of an Aircraft in Flight?
- Airspeed.
- Wing’s Angle of Attack.
During an Updraught an Aircraft will?
Climb.
During a Downdraught an Aircraft will?
Sink.
Define Microbursts?
Associated with intense Thunderstorms and includes all forms of Windshear?
What should a Pilot do if Microburst activity is found in the vicinity of the Aerodrome?
Abort Approach / Delay Take-off.
What should a Pilot do if you encounter an area of intense precipitation ahead of you on Final Approach?
Initiate a Go-Around.
Define Jet Stream?
Very long narrow bands of fast moving air just beneath the Tropopause.
What kind of Turbulence is created from Jet Streams?
Clear Air Turbulence.
The highest change of speed occurs on the side of the Jet Stream adjacent to the ‘____’?
Cold Air.
What countermeasures should be used where on Final Approach with expected Windshear (4)?
- Increase Power.
- Raise the Nose.
- Co-ordinate Pitch and Power.
- Prepare for Missed Approach.
What countermeasures should be used where on Take-off with expected Windshear (4)?
- Recognise Threat quickly and commit to appropriate action.
- Follow Operations/Aircraft Flight Manual Techniques.
- Use Maximum Power.
- Adopt appropriate pitch angle and hold. Do Not chase the Airspeed.
What is the most sensible course of action with expected Windshear during Final Approach?
Delay Landing / Divert to alternative Airport.
What is the most sensible course of action with expected Windshear during Take-off?
Delay Take-off until Windshear has diminished.
