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JH MET REVISION Flashcards

1
Q

What are the ISA values for the following?

  • Temperature at MSL
  • Temperature lapse rate
  • Pressure at MSL
  • Pressure lapse rate
  • Air density
A
  • MSL Temp = 15 degrees C
  • Temp lapse rate = decrease of 2 degrees C per 1000ft
  • Px at MSL = 1013.25 hpa
  • px lapse rate = decrease 1 hpa per 30ft
  • Air density = 1.225 kg per m3
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2
Q

What 4 factors affect air density?

A

Gravity
Air pressure
Temperature
Humidity

GATH

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3
Q

A reduction of air density affects helicopters in 4 important ways, what are they?

A
  • power available reduces
  • power required increases
  • handling deterioates
  • stability is reduced
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4
Q

When calculating DA using the formula; DA=PA +/- (120t), what does t represent?

A

T= difference in temperature between the ISA for that pressure altitude and the outside air temperature

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5
Q

How does pressure gradient force cause air to move?

A

Causes air to move along the ground from high px regions to low px regions.

It dictates wind speed

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6
Q

What are the 2 main causes of turbulence in the lower part of the atmosphere?

A

Strong winds affected by friction and obstructions to the airflow (buildings, trees etc) (MECHANICAL TURBULENCE)

Heating of the air at the surface causes convection currents. The updraught in cells is marked by CU clouds

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7
Q

What are the winds called that flow UP and DOWN slopes in moutainous areas?

A 
Up = anabatic
Down = katabatic
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8
Q

If moist air flows up and over a mountain range, forms clouds and deposits rain, how will its characteristics differ on the downward(lee) side?

A

The resulting air and wind is drier and warmer

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9
Q

What is the fohn effect

A

The term used to describe the increase in temperature and decrease in humidity that follows a moist air mass having moved over a mountain range

  1. Air is forced upwards and cools at the DALR (3 degrees/1000ft)
  2. Moist air is cooled at the SALR (1.5 degrees/1000ft) as it rises
  3. Moisture condenses, forms clouds, produces rain, removes moisture from airflow
  4. Descending air is initially still saturated and warms at SALR
  5. Below cloudbase air warms at DALR
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10
Q

What lapse rates are assumed when considering air involved in the fohn effect

A

SALR - saturated adiabatic lapse rate (1.5 degree / 1000ft)

DALR - dry adiabatic lapse rate (3 degrees / 1000ft)

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11
Q

What is meant by orographic uplift?

A

Orogrpahic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain

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12
Q

What is a trigger action in connection with thunderstorms

A

Its is one if the conditions that will set off a thunderstorm.
4 types
- convection - surface air heated, becomes less dense and rises
- orographic uplift - unstable, moist air forced aloft by upslope of terrain
- convergance - winds come together forcing air to concentrate and move upward
- mass ascent - cold air mass drives warm air mass upwards

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13
Q

What does nimbo in a cloud name mean?

A

Rain. Nimbo is latin for rain

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14
Q

Which 4 main types of cloud occur in the helo enviroment?

A
  1. Stratus
  2. Cumulus
  3. Stratocumulus
  4. Cumulonimbus
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15
Q

What 4 actions trigger thunderstorms

A

Convection - surface air heated, becomes less dense and rises

Orographic uplift- unstable moist air forced aloft by upslop terrain

Convergance- winds come together forcing air to concentrate and move upward

Mass ascent- cold air mass drives warm air mass upward

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16
Q

What is an occlusion

A

A combined warm and cold air mass front

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17
Q

What does WHISTLE stand for in relation to thunderstorms

A 
Weather
Hail
Icing
Squall line
Turbulence
Lightening
Electricity
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18
Q

What are the 4 types of airframe ice formation

A

Hoar frost
Rime ice
Clear ice
Mixed ice

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19
Q

In what temperature range is severe airframe icing most likely to occur

A

0 to -20

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20
Q

What are the early indications of rotor blade ice accretion that the pilot will experience?

A

Rise in Trq to maintain rotor rpm as pwr required to over come increase in rotor drag and increased wgt.

Vibrations in the aircraft

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21
Q

What are supercooled water droplets?

A

Droplets that have remained liquid although they are below freezing

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22
Q

Which type of icing has white opaque appearance with frost like surface

A

Rime ice

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23
Q

What does CAVOK Mean?

A

Cloud and visibility okay.

Vis is 10k or more
No min vis reported
No cloud below 5000ft or below min sector alt
No cb or tcu at any hgt
No significant weather in the vicinity of the aerodrome

24
Q

When a trend is added to a METAR, how long is it added for?

A

Valid for the 2 hour period after the observation

25
What does MOMIDS stand for?
Met office military information dissemination system
26
Which met office system probides information on light levels
MONIM | Met office night illumination model
27
As alt increase what differences can be seen in engine compressor speed and turbine temperature if the pilot maintains the same torque?
Lower density, engine needs to work harder, higher compressor speed, turbine temperature will run high.
28
The vis is 12km and base of lowest cloud is (3 oktas or more) 3000ft AGL. What is the colour code?
BLU
29
For how many statute miles around an airfield is a TAF valid for ?
5
30
How is cloud with a temp below 0 degrees C represented on an airfield weather x section
Red hash lines through the cloud
31
What does Tempo mean in a TAF
Temporary
32
How must aoa change as alt is increased iot maintain lift?
Aoa must increase/ get steeper
33
What colour code falls between blu and grn
White
34
Which maritime air masses affecting the UK will bring the best and worst vis?
Polar maritime - good outside showers Polar continental winter - good outside showers Artic Maritime - good outside showers rPm - mainly good Tropical maritime - moderate to poor Tropical continental - reduced vis in haze Polar continental summer - mod to poor
35
What is the fundamental difference between a TAF and a METAR?
A TAF is a FORECAST, a METAR is a REPORT
36
What does a lack of cumulus cloud probably indicate about airmass stability?
Stable airmass
37
What is generally meant by slant visibility?
The greatest distance a specified target can be seen when viewed at an angle and is affected bu obscuring phenomenon such as fog, haze or mist
38
How does the presence of an inversion affect dispersal of smoke / industrial haze?
Temperature inversion may contain the smoke near the surface, reducing visibility near the source
39
How many symbols of any particular percipitation type ate used in a station circle to indicate moderate intensity
3
40
What are the variables that affect air density
Temperature Pressure Humidity
41
3 types of wind
Eddies - breakup of airflow Gusts - sudden increase in wind speed temporarily Squall - increase in wind speed, lasts longer, associated with percipitation
42
What are significant cloud characteristics
Base, Depth, Temp
43
How does cloud form
``` Mass ascent -convection -convergence Orographic uplift Turbulent mixing ``` Moist air rises, cools, condenses
44
What hazards are associated with clouds
Low vis Percipitation Icing Increased wind and turbulence
45
What 3 things are required for clouds to form
Adequate water vapour Condensation nuclei (dust, smoke, salt particles) Method for air to be cooled
46
At what wind speed should you expect sand movement?
20kts
47
Below what visibilty is a sandstorm declared?
1000m
48
At what wind speed should you expect dust to move?
15kts
49
What hgt does dust haze extend to? And what does this mean for vis?
10,000ft Rarely reduces vis to less than 1000m
50
For a helo to generate its own white out/brown out what should the wind be?
Light, less than 15kts
51
What is the intensity of percipitation classified as? And what does it depend on?
Classified as, slight, moderate or heavy ``` Depends on Vertical thickness of the cloud Water content of the cloud Strength of updrauggts within cloud Topography ```
52
What hazards can be cause by percipitation?
``` Lowering of cloud base Strong down currents of air Reduced vis Accumulation of packed snow Hail damage to ac Flooded or slippery landing / taxying surfaces ```
53
Describe the thunderstorm formation process
1. Formed from Cumulus clouds with extensive vertical development 2. Build into cumulonimbus clouds - contain large amounts of moisture and unstable air - produce hazardous weather phenomena Conditions required 1. Unstable layer extending to high alts 2. High moisture content 3. Trigger action
54
What affects the way ice forms on the rotors?
1. Temperature 2. Liquid content and droplet size 3. Kinetic energy 4. Blade section 5. Mechanical flexion and vibration
55
Between what temp will ice begin to naturally form on the rotor blade leading edges? And what % of the edge will be affected
0 to -3 ice will form in natural icing conditions on the leading edge of the blades 70% of the leading edge will be affected
56
What are the effects / results of instruments in icing conditions
1. Trq rises with the collective in the same position 2. Loss of hgt (or change in collective position with hgt hold engaged) 3. Changes in trq as ice builds and sheds 4. Heated ports (pitot and static) must be on

Met (5 decks)

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