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FSS1601 AK3 > AV22: Visibility and Icing - HS > Flashcards

AV22: Visibility and Icing - HS Flashcards

1
Q

Visibility

A

The maximum distance at which we can see and identify an object of suitable dimensions. Used to describe the transparency of the atmosphere.

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2
Q

Prevailing visibility

A

The maximum visibility at eye level common to at least half of the horizon circle. Also referred to as horizontal visibility.

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3
Q

Tower visibility

A

The maximum distance at which an object of suitable dimensions can be seen and identified at the level of the tower cab.

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4
Q

Vertical visibility

A

The distance one can see vertically into a surface based layer.

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5
Q

Flight visibility

A

The average distance one can see forward from an AC in flight.

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6
Q

Slant visibility

A

The farthest point on the ground one can see from an AC in flight.

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7
Q

RVR

A

Runway Visual Range: The computed maximum visibility along the runway at cockpit level.

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8
Q

How does stability of the air affect visibility?

A

Almost all restricting phenomena are more pronounced in stable air.

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9
Q

Why does stable air make for lower visibility?

A
  • Impurities are trapped in the lower layers
  • Continuous precipitation from layer clouds reduce visibility
  • Favourable for drizzle and fog
  • Particles are not lifted above eye level (drifting phenomena)
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10
Q

How can unstable air make for lower visibility?

A
  • Showery precipitation

- BLSA, BLSN, BLDU

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11
Q

Cause of smoke

A

Industrial centres or forest fires

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12
Q

Stability of air when smoke is reducing visibility

A

Stable

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13
Q

Dissipation factors for smoke

A
  • Changing of air mass
  • Change of wind direction
  • Increase in wind speed
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14
Q

Cause of haze

A

General pollution

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15
Q

Stability of air when haze is reducing visibility

A

Stable warm air mass

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16
Q

Dissipation factors for haze

A
  • Changing of air mass
  • Change of wind direction
  • Increase in wind speed
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17
Q

Cause of BLSN, BLSA, BLDU

A

Windy conditions

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18
Q

Stability of air when BLSN is reducing visibility

A

Unstable

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19
Q

Dissipations factors for BSLN

A

Decrease in wind speed

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20
Q

Cause of radiation fog

A

Night time cooling

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21
Q

Stability of air when radiation fog is reducing visibility

A

Stable

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22
Q

Dissipation factors for radiation fog

A
  • Daytime heating

- Increase in windspeed

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23
Q

Cause of advection fog

A

Advected warm air over cool water or land

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24
Q

Stability of air when advection fog is reducing visibility

A

Stable

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25
Q

Dissipation factors for advection fog

A
  • Change in wind direction
  • Strong winds
  • Daytime heating (when over land)
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26
Q

Cause of upslope fog

A

Orographic lift (adiabatic cooling)

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27
Q

Stability of air when upslope fog is reducing visibility

A

Stable

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28
Q

Dissipation factors for upslope fog

A
  • Change of wind direction

- Strong winds

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29
Q

Cause of frontal fog

A

Frontal precipitation (evaporation of precipitation)

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30
Q

Stability of air when frontal fog is reducing visibility

A

Stable

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31
Q

Dissipitation factors for frontal fog

A

Passing of the front

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32
Q

Cause of steam fog

A

Cold air over warmer water

33
Q

Stability of air when steam fog is reducing visibility

34
Q

Dissipation factors for steam fog

A
  • Change in wind direction

- Strong winds

35
Q

Cause of SHRA, SHSN, SHGS

A

Convective cloud

36
Q

Stability of air when SHRA, SHSN, SHGS is reducing visbility

37
Q

Dissipation factors for SHRA, SHSN, SHGS

A

End of precipitation

38
Q

Cause of DZ, FZDZ, SG, RA, FZRA, SN, IC

A

Stratiform cloud

39
Q

Stability of air when DZ, FZDZ, SG, RA, FZRA, SN, IC is reducing visibility

40
Q

Dissipation factors for DZ, FZDZ, SG, RA, FZRA, SN, IC

A

Movement of cloud

41
Q

How does thin fog or surface based haze affect different visibilities?

A
  • Poor horizontal
  • Good vertical
  • Good slant
  • Good flight
42
Q

How does thick fog affect different visibilities?

A
  • Poor horizontal
  • Poor vertical
  • Poor slant
  • Poor flight
43
Q

How doe smoke or haze aloft affect different visbilities?

A
  • Good horizontal
  • Good vertical
  • Poor slant
  • Poor flight
44
Q

What are the three main types of airframe icing?

A

Hoar frost, clear icing, rime icing

45
Q

Hoar frost during flight

A

Forms after a sudden descent into warmer air or a rapid climb through an inversion

46
Q

What conditions are required for icing to occur?

A
  • Temperature of aircraft must be less than 0
  • The AC must be above the freezing level
  • The AC must strike the super-cooled water droplets
47
Q

Where does the most serious cloud icing occur?

A

In the upper half of thunderstorm cells approaching the mature stage. The strong vertical currents carry large supercooled water droplets aloft to regions of low temperatures.

48
Q

When precipitation occurs, what happens to the risk of in cloud icing?

A

It decreases because the cloud’s water content is less.

49
Q

Although icing from stratiform cloud is less severe, what gives it potential to be a major hazard?

A

Icing areas are great in the horizontal extent, so it can become hazardous if the AC is in the icing area for a long period of time.

50
Q

Icing in orographic clouds

A

Often produce more serious icing situations than normal because of the more pronounced lifting.

51
Q

How is freezing rain formed?

A

When rain falls from an above freezing layer to a below freezing layer and become super-cooled water droplets. The cold layer is not thick enough for the drops to freeze.

52
Q

What do ice pellets indicate?

A

Freezing rain aloft. (Because the cold layer was thick enough to completely freeze the super-cooled water droplets)

53
Q

Why are ST and SC cloud layers formed over water a concern?

A

Because they have a high water content and therefore a serious icing risk.

54
Q

Where is icing most severe in an SC cloud formed by mechanical turbulence?

A

Just below the top.

55
Q

Where is icing from FZDZ usually encountered?

A

In the cloud, but most severely just below the cloud base.

56
Q

How do snow and ice crystals affect the AC?

A

They usually arent a problem, but can melt when in contact with warm parts of the AC and then refreeze. Wet snow can stick to the AC and alter the shape of the wings.

57
Q

In which cloud form is icing not a risk?

58
Q

What is the most dangerous type of icing?

A

Clear icing

59
Q

Where does clear icing occur?

A

In CBs and in FZRA

60
Q

What are the six factors for seriousness of icing?

A
  • Air temperature
  • Aircraft type (shape and speed)
  • Temperature of AC skin
  • Size of supercooled water droplets
  • Amount of supercooled water droplets
  • Amount of time spent in conditions
61
Q

What are the intensities of icing?

A
  • TR
  • LGT
  • MDT
  • SEV
62
Q

Trace icing

A

The rate of accretion is slightly greater than the rate of sublimation. Not hazardous unless encountered for an extended period of time.

63
Q

Light icing

A

Occasional use of de-icing and anti-icing equipment removes and prevents accretion. Does not present a problem if dealt with properly.

64
Q

Moderate icing

A

The rate of accretion is such that even short encounters become potentially hazardous and use of de-icing and anti-icing equipment or diversion is necessary.

65
Q

Severe icing

A

The rate of accretion is such that the use of de-icing and anti-icing equipment fails to reduce or control the icing hazard. Immediate diversion is necessary.

66
Q

What effects does icing have on the aerodynamic characteristics of an AC?

A
  • Lifting force decreases
  • Forward thrust decreases
  • Weight increases
  • Drag increases
67
Q

What effect does icing on the prop blades have on the performance of the AC?

A

The icing reduces thrust. If it is uneven it disrupts the balance of the propeller which causes vibrations and forces the pilot to reduce power.

68
Q

How does icing on the windshield and canopy affect flight?

A

Reduces pilots ability to see out the windshield.

69
Q

How does icing on the aerials affect flight?

A

When it builds up, it can cause antennas and radio masts to vibrate and break off, leading to a loss of communication when it is essential.

70
Q

How does icing on pitot tubes and static ports affect flight?

A

Ice can block these sensors causing erroneous readings of airspeed, altimeter and other instruments.

71
Q

What causes carburetor icing?

A

Occurs because of cooling through evaporation of the fuel and a lowering of the pressure when the air’s moisture content is high and the temperature is above freezing.

72
Q

How does carburetor icing affect flight?

A

The icing robs the engine of air reducing thrust and possibly resulting in engine failure.

73
Q

How does icing on turbine engines affect flight?

A
  • reduces aerodynamic efficiency
  • causes vibrations
  • causes a loss of thrust
  • can cause engine failure
  • block air inlets
74
Q

How does ice accretion differ between high and low speed AC?

A

Ice builds up more on high speed AC because of their thin wings. Luckily, they spend less time in the icing region because they travel more quickly.

75
Q

Airfoil shape and icing

A

Airfoils with a big radius of curvature disrupt the airflow causing the smaller supercooled water droplets to be carried around the airfoil by the air stream, resulting in less icing. (More icing on thinner wings)

76
Q

Speed and icing

A

The faster the AC, the less chance the droplets have to be diverted around the airfoil by the air stream.

77
Q

Droplet size and icing

A

The larger the droplet, the more difficult it is for the air stream to displace it.

78
Q

Icing and helicopters

A
  • Rotor blades must be perfectly balanced
  • Icing builds up quickly because of how thin the blades are and how quickly they rotate
  • Uneven ice shedding causes vibrations

FSS1601 AK3 (16 decks)

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