Turbulence Flashcards

1
Q

How does mechanical turbulence occur?

A
  • When air flows near the surface, it will be disturbed by irregular features like hills and buildings.
  • An irregular pattern of eddies will be superimposed on the streamlined airflow, causing gusts and lulls.
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2
Q

What does the amount of mechanical turbulence depend upon? (2)
How high do light winds and strong winds produce turbulence respectively?

A
  • Wind speed and roughness of the terrain.
  • Light winds may produce a layer of turbulence only a few hundred feet thick, but stronger winds will produce increased turbulence up to higher levels.
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3
Q

What is the largest cause of mechanical turbulence?

A

Mountains.

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4
Q

How does thermal turbulence work? (3)

A
  • Surface air is heated by the Earth and rises as convective currents.
  • This warmer air rises and cools as a function of height, until it reaches a level of ai with the same temperature, where it will spread horizontally.
  • Descending air over those areas that are relatively cold, will replace the ‘convected’ air from the ground.
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5
Q

How do thunderstorms cause wind shear?

A
  • Through updraughts and downdraughts inherent in the thunderstorm.
  • The updraughts and downdraughts will cause the aircraft to experience gusts, which are localised irregular air flows within the draught.
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6
Q

When are updraughts the strongest in a thunderstorm?

A

When the TS is still developing.

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7
Q

What are the dangers of a downdraught during a thunderstorm?

A
  • Downdraughts are deflected horizontally at the ground under the cloud and spread ahead of the cloud.
  • The deflected down draught will appear as a cold gusty wind.
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8
Q

How do thunderstorms cause windshear?

A

Due to its divergent flow near the ground, and its powerful downdraughts, windshear can occur.

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9
Q

When is windshear mainly experienced?

A

Most critical and mainly experienced during take-off and landing.

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10
Q

What is positive windshear?

What is negative windshear?

A
  • Positive windshear is an increase in IAS.

- Negative windshear is a decrease in IAS.

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11
Q

What happens if there is a reduction in headwind speed during landing? (2)

A
  • Aircraft will increase its rate of descent.

- Aircraft will fall below intended glide path because the sudden drop in headwind results in loss of lift.

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12
Q

What happens if there is a reduction in headwind speed during take-off?

A

Windshear will reduce the amount of lift available to the aircraft, sinking the aircraft below the intended climb out path.

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13
Q

Where is low-level windshear usually located? (2)

A
  • Junction of warm and cold air.

- Sea breeze fronts.

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14
Q

What is Clear Air Turbulence?

A

Turbulence produced by windshear at higher levels due to the formation of clouds.

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15
Q

How does the leeward side of mountains cause windshear?

A
  • Due to strong winds from leeward slopes, this can cause windshear.
  • Stagnant air is also found over the plane in the lee of a mountain range, causing windshear.
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16
Q

How does ‘stagnant air’ affect an aircraft on approach? (2)

A
  • Severe windshear will be encountered when aircraft penetrate stagnant air from above.
  • Loss in altitude can occur as well as IAS decreasing.
17
Q

How is wake turbulence formed and what does it trigger?

A
  • Caused by pressure differential between upper and lower wing surfaces of aircraft.
  • Triggers a roll up of the airflow, aft of the wing, resulting in swirling air masses trailing downstream of the wing tips.
18
Q

What is the strength of wake turbulence determined by? (2)

A
  • Weight, speed and pitch of the aircraft’s wing.

- Weight of the aircraft.

19
Q

What are the dangers associated with wake turbulence?

A
  • Vortex from a large aircraft sinks at a given rate and levels off below the flight path of the generating aircraft.
  • Wake can impose rolling moments (roll the aircraft like a boat, imagine it) exceeding the roll control capability of aircraft, which may cause damage to equipment.
20
Q

How do you avoid wake turbulence? (4)

A
  • Change altitude.
  • Move laterally i.e. to the side away from the preceding aircraft’s position.
  • Obey ATC instructions.
  • Following the correct separation limits.