12. Turbulence Flashcards
Turbulence
“A sharp change in wind speed or direction over a short distance, vertically or horizontally, and is the cause of turbulence”
This is the definition of what
WINDSHEAR
1
Turbulence
“a significant sharp change in wind speed or direction over a short distance below the height of 1600 ft above ground level (final approach and take off/initial climbout)”
This is the definition of what
LOW LEVEL WINDSHEAR
1
Turbulence
“encountered when climbing or descending when, as example, leaving the top of an inversion. Usually measured in knots per hundered feet (Kt/100ft)”
This is the definition of what
VERTICAL WINDSHEAR
2
Turbulence
Complete the correct speed in knots for the following ICAO charactersitics of wind shear table;
- LIGHT ____ to ____kts inclusive per 30m (100ft)
- MODERATE ____ to ____kts inclusive per 30m (100ft)
- STRONG ____ to ____kts inclusive per 30m (100ft)
- SEVERE above ____kts inclusive per 30m (100ft)
- LIGHT 0 to 4 kts inclusive per 30m (100ft)
- MODERATE 5 to 8 kts inclusive per 30m (100ft)
- STRONG 9 to 12 kts inclusive per 30m (100ft)
- SEVERE above 12 kts inclusive per 30m (100ft)
- REMEMBER Significant number is “4”
- 4 windshear speeds
- Incremenets of 4 starting from 0
3
Turbulence
“a term used in conjunction with sudden intermittent increases in the wind speed near the surface levels - an irregularity in wind speed that creates eddy currents disrupting smooth airflow”
This is the definition of what
GUSTINESS
3
Turbulence
The rapid change of wind direction and/or speed that takes place in wind shear can have the following effects on an aircraft;
- An INCREASE or DECREASE in headwind or an INCREASE or DECREASE in tailwind results in an effective increase in air speed and the aircraft will climb
- An INCREASE or DECREASE in headwind or an INCREASE or DECREASE in tailwind results in an effective decrease in air speed and the aircraft will sink
- An updraught or downdraught can result in unwanted ____ and ____ and the loss or gain of airspeed
- A CROSSWIND or DOWNDRAUGHT resulting in the aircraft drifting from the desired flight path
- DECREASE headwind / INCREASE tailwind
- INCREASE headwind / DECREASE tailwind
- CLIMB and DESCENT
- CROSSWIND
3
Turbulence
During a temperature inversion situation when passing the transition area from the cold to higher warmer air;
- The engines will suddenly produce MORE or LESS power
- There will be MORE or LESS aerodynamic lift
- Will have a POSITIVE or NEGATIVE effect on aircraft performance
- LESS
- LESS
- NEGATIVE
- The aircraft is flying from denser colder air into a warmer, less dense layer
- This means less air in the engines would need more thrust to maintain speed
- Less dense air means less lift
- If there is less lift and drop in airspeed and more thrust is needed, this means that more fuel is used, so performance decreases
4
Turbulence
What is the name of a ground-based system used to detect wind shear and associated weather phenomena such as microbursts close to an airport
LOW LEVEL WIND SHEAR ALERT SYSTEM
(LLWAS)
4
Turbulence
In a low level windshear alert system,
- anemometers sample sensors how regularly?
- A centre field sensor produces a running mean surface wind over what time period
- An audio-visual alarm is triggered if vector differences between the center field and perimeter sensor are more than ____kts,
- Warnings of wind shear are promulgates on the ATIS or on regular ____ and ____ reports
- 10 SECONDS
- 2 MINUTES
- 15 KTS
- METAR and SPECI
4
Turbulence
“the variation in the wind along the aircrafts flight path or pattern, intensity and durection that disturbs the aircrafts attitude about its major axis but does not significantly alter the flight path”
This is a definition of what
TURBULENCE
5
Turbulence
The common types of turbulence are;
[ ] Clear Air Turbulence (CAT)
[ ] Dry Omnidirectional Gusts (DOG)
[ ] Convective
[ ] Convergent
[ ] Mechanical
[ ] Orgraphic
[ ] Frontal
[ ] Pacific Gust Ridge
[X] Clear Air Turbulence (CAT)
[ ] Dry Omnidirectional Gusts (DOG)
[X] Convective
[ ] Convergent
[X] Mechanical
[X] Orgraphic
[X] Frontal
[ ] Pacific Gust Ridge
5
Turbulence
Turbulence will normally be found or associated with;
[ ] Rough ground surfaces
[ ] Mountains
[ ] Flat farmland
[ ] Inversion layers
[ ] Cold stable air
[ ] CB clouds
[ ] AS clouds
[ ] Thunderstorms
[ ] Unstable layers
[ ] Jetstreams
[ ] Troughs and Ridges
[X] Rough ground surfaces
[X] Mountains
[ ] Flat farmland
[X] Inversion layers
[ ] Cold stable air
[X] CB clouds
[ ] AS clouds
[X] Thunderstorms
[X] Unstable layers
[X] Jetstreams
[X] Troughs and Ridges
5
Turbulence
Marry up each for the following turbulance formation descriptions to the relevent turbulance type;
- Turbulenve movement of air masses in the absence of any visual cues such as clouds, and is caused when bodiges of air moving at widely different speeds meet [ ]
- Currents resulting from insolation. Different surfaces have differing abilities in absorbing or reflecting head called the ‘Albedo Effect’. Barren surfaces such as sandy and rocky wastelands and ploughed fields become hotter than ground covered by vegetation [ ]
- Physical obstructions interrupt the normal flow of air i.e. hills, mountains, trees, buildings. Depends on the windspeed and roughness of the obstructions [ ]
- Occurs when (a) wind direction is +/- 30° to a mountain range (b) wind speed at the summit is at least 15 kts (speed increasing as altitude increases) (c) there is a marked layer of stability around the altitude of the summit which prevents air continuously rising. “Rotors” form below the elevation of the mountain peaks [ ]
- A sudden change in wind direction of 20° or so at the frontal surface. [ ]
- CLEAR AIR (CAT)
- CONVECTIVE (Thermal)
- MECHANICAL
- OROGRAPHIC
- FRONTAL
Turbulence
Marry up each for the following turbulance “where usually found” descriptions to the relevent turbulance type;
- High tropopause at altitudes of around 23,000-39,000 ft. Encountered most frequently in regions of jet streams. May occur near mountain ranges at lower altitudes. If air is to dry for cloud to form, visual cues are missing. [ ]
- Obstructions such as buildings, trees, and rough terrain disrupt smooth wind flow and eddies are developed [ ]
- Passing through a warm to cold sector at the surface, usually accompanied with wind shear [ ]
- May extend 100 miles or more downwind from the barrier. Wave crests extend well above the highest mountains, sometimes in the lower stratosphere. Turbulence can be violent in the overturning rotor, with updrafts and downdrafts in waves creating extremely violent turbulence [ ]
- Greatest around 1500hrs on clear sunny days. Localised vertical air movements ascending and descending. Does not occur over sea [ ]
- CLEAR AIR (CAT)
- MECHANICAL
- FRONTAL
- OROGRAPHIC
- CONVECTIVE (Thermal)
Turbulence
In turbulence, an aircrafts speed will fluctuate. To prevent speed going above the maximum or below the minimum speed range, what should a pilot do when flying through turbulence
REDUCED TO MIDDLE OF PERMITTED RANGE SPEEDS
7
Turbulence
Turbulence
“Conditions less than moderate turbulence. Changes in accelerometer readings less than 0.5 g at the aircraft’s centre of gravity.”
This is a definition of which of the 3 categories of turbulence
LIGHT TURBULENCE
Turbulence
“Conditions in which moderate changes in aircraft attitude and/or altitude may occur but the aircraft remains in positive control at all times. Usually, small variations in air speed. Changes in accelerometer readings of 0.5 g to 1.0 g at the aircraft’s centre of gravity. Difficulty in walking. Occupants feel strain against seat belts. Loose objects move about.”
This is a definition of which of the 3 categories of turbulence
MODERATE TURBULENCE
Turbulence
“Conditions in which abrupt changes in aircraft attitude and/or altitude occur; aircraft may be out of control for short periods. Usually, large variations in air speed. Changes in accelerometer readings greater than 1.0 g at the aircraft’s centre of gravity. Qccupants are forced violently against seat belts. Loose objects are tossed about.”
This is a definition of which of the 3 categories of turbulence
SERVE TURBULENCE
Turbulence
Maximum CAT occurs where the windshear is the greatest which is where;
- LEVEL WITH OR JUST BELOW or LEVEL WITH OR JUST ABOVE the height of the jet core
- In WARM or COLD are on the WARM or COLD side of the jet
- LEVEL WITH OR JUST BELOW
- WARM AIR / COLD SIDE
- Typical question will say where is the most significant CAT encountered, whcih is typically the polar side IN the tropical side.
- The cold air side of the jet is the lower pressure side of the jetstream at height
8
Turbulence
The core of a jetstream is typically how thick;
[ ] 5000 ft
[ ] 6000 ft
[ ] 7000 ft
[ ] 8000 ft
[ ] 5000 ft
[X] 6000 ft
[ ] 7000 ft
[ ] 8000 ft
8
Turbulence
What is the most reliable source of information relating to turbulance;
[ ] METAR
[ ] PIREP
[ ] AIRMET
[ ] VOLMET
[ ] METAR
[X] PIREP
[ ] AIRMET
[ ] VOLMET
- PIREP is a pilot report
- Pilot reports of turbylence are a very valuable source of information
9
Turbulence
When looking at the diagram of surface isobars around the NH frontal system, why should it be obvious that there would be associated turbulence at the area of the front
CHANGE IN WIND DIRECTION OF +20°
- a suddent change in wind direction will result in turbulence
10
Turbulence
The most significant hazard generated by frontal windshear comes at HIGH or LOW level when teh aircraft is passing through the frontal surface in what 2 circumstances
- LOW LEVEL
- APPROACH TO LANDING or TAKE-OFF
- The below diagram demonstrates the issue of a frontal winshear on approach to landing
- The change in wind direction equates to a drop off of 10 kts IAS
- As the aircraft passes through the front, airspeed will drop off, aircraft will sink
- There is now an apparent cross wind so this may produce control difficulties
Turbulence
The low pressure and convergenceassociated with a through is likely to produce convective cloud, showers and thunderstorms. For this reason VERTICAL or HORIZONTAL windshear associated with a trough may be masked by turbulence generated by cloud
HORIZONTAL
Turbulence
Look at the following diagram. Knowing that surface convergence generates convective cloud and surface divergence does not, turbulence in this scenario is likely to be masked;
- IN CLOUD or CLEAR AIR over Africa
- IN CLOUD or CLEAR AIR over Italy
- CLOUD over Africa
- CLEAR AIR over Italy
Turbulence
- During the morning period, wind speed and turbulence will INCREASE or DECREASE
- Calmest flying condfitions are EARLY MORNING or MID-AFTERNOON
- Convective turbulence is strongest EARLY MORNING or MID-AFTERNOON
- INCREASE
- EARLY MORNING
- EARLY MORNING
- Think of the diurnal effect
- Ground is cold first thing in the morning having radiated heat away through the night
- As it starts to warm, gradually air is warmed and will start to rise, creating depressions
- This gives rise to the air movement and with it turbulence
14
Turbulence
What are the recommended turbulence avoidance limits associated with thunderstorms;
- Visual flight - avoid by ____nm
With weather radar, avoid echos by;
* Between 0 to FL250; by ____NM
* Between FL250 to FL300; by ____NM
* Over FL300; by ____NM
* In both cases, clear tops by at least ____ft
- Visual flight - avoid by 10 nm
With weather radar, avoid echos by;
* Between 0 to FL250; by 10 nm
* Between FL250 to FL300; by 15 nm
* Over FL300; by 20 nm
* In both cases, clear tops by at least 5000 ft
- NOTE weathe radar echoes show the core of the cloud, not the edge
- This is why the avoidance limits are greater with weather echos
15
Turbulence
Cold air descending from a thunderstorm can run ahead of the storm producing a mini COLD or WARM front known as a gust front, which brings which hazards with it;
[ ] Orographic lifting
[ ] Windhsear
[ ] Turbulence
[ ] Squall conditions
[ ] sleet
[ ] Orographic lifting
[X] Windhsear
[X] Turbulence
[X] Squall conditions
[ ] sleet
16
Turbulence
Gust fronts associated to a thunderstorm can extend as far as ____ to ____ km (____ to ____NM), and up to ____ft
- 25 to 30 KM
- 15 to 20 NM
16
Turbulence
Turbulence inside a thunderstorm is a result of updrafts and downdrafts;
- Updraft speeds of ____kts
- Downdraft speeds of ____kts
- Turbulence will be ____
- 60 KTS
- 40 KTS
- MODERATE to SEVERE
17
Turbulence
What does Doppler radar measure in order to get a measure of turbulence in cloud
RAINDROP MOVEMENT
17
