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Flashcards in 305 Deck (14)
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1
Q

5 factors involved in the formation type and intensity of icing

A
temperature
moisture
nuclei
lift
stability of air
2
Q

temperature

A
  • requires sub-zero temperatures (air and airplane)
  • super-cooled water droplets which are common down to -15c and cease around -20c
  • most supercooled water disappears -30c and -40c
3
Q

moisture

A
  • water vapour will not produce significant icing, only hoar frost
  • super-cooled water is the main concern for forecasting icing, but it must be inferred
  • Large bodies of water can effect icing through heat and moisture fluxes - if there is convection or FZDZ icing could be MDT MXD or worse
  • otherwise rime icing is likely
4
Q

LWC

A

liquid water content- is a measure of the density of water-based cloud.

5
Q

Nuclei

A
  • ice nuclei and ice crystals grow at the expense of supercooled water droplets
  • the greater amount of freezing nuclei, the lower the threat of icing
  • icing is at it’s peak at temperatures close to freezing
6
Q

Lift

A
  • Mechanical, convective or synoptic
  • the stronger the lift, the bigger the droplet size
  • the greater the intensity of lift, the greater the liklihood that clear icing will occur
7
Q

Strong lift is found in:

A
  • Strong synoptic features - intense deep lows, sharp troughs
  • Unstable clouds - ACC, TCU, CB
  • orographic clouds
8
Q

Stability of the air

A
  • Upward motion will form and support more abundant and larger water droplets.
  • Concentration of LWC will be higher in thicker cloud
  • cloud associated with stable air is usually thinner but spread over a large horizontal area, also can be close to the ground. Critical for arrival and departure procedures.
  • Unstable air sustains upward vertical motion giving larger water droplets
  • LWC can vary at different levels of unstable cloud types giving different intensities and types of icing
9
Q

Clouds associated with icing:
Thin Stratiform
F, ST, thin AS

A
  • stable structure
  • large horizontal, small vertical extent
  • usually no precip
  • low LWC, small droplets
  • low prob
  • LGT, RIME only
  • 0c to -15c only
  • *thicker ST can produce DZ/FZFD, which could give MDT MXD or CLR in lower levels
10
Q

Clouds associated with Icing:
Thick Stratiform
AS, NS

A
  • associated with warm frontal zones
  • continuous advection of moisture up frontal surface
  • precipitation or lack of is not an indication of icing
  • intensity affected by strength of vertical velocity
  • high LWC
  • no icing in CS
  • high probability of icing
  • LGT to MDT (SEV within 150 to 250 ahead of front)
  • RIME
  • SVR CLR possible close to front in FZRA
11
Q

Clouds associated with icing:
Weak cumuliform
CU,SC,AC

A
  • Some stability, usually capped by an inversion
  • can have some areas of moderate ascent
  • dependent on source region
  • consider age/composition of cloud
  • high LWC, varying droplet size
  • 50% probability of icing
  • intensity depends on level of instability LGT-MDT
12
Q

Clouds associated with icing:
Strong cumuliform
TCU,CB, ACC

A
  • often associated with cold frontal zones
  • very unstable
  • high vertical velocities
  • supports and carries large super-cooled water droplets to high altitudes and cold temperatures
  • highest icing intensities just before surface showers
  • hazards diminish as ice crystals multiply, precip occurs, downdrafts
  • large vertical small horizontal extent
  • probability near 100%
  • MDT-SEV
  • MXD-CLR
13
Q

Impacts of aircraft icing:

A
  • Loss of climb capability
  • reduced visibility
  • increased weight/decreased lift
  • increased drag/stall speed
  • increased fuel consumption/decreased range
  • accretion will be greater and faster on vertical and horizontal stabilizers than on wings
  • airflow separation will affect control surfaces
  • pitot and static ports can get blocked
14
Q

Common Icing counter measures

A
  • pitot and carb heat
  • small cockpit controlled heaters
  • heating elements
  • leading edge airblead
  • pnuematic booties
  • inflatable bladders
  • in flight de-ice liquid application, in flight and during T/O and landing
  • Visual inspection of aircraft and control surfaces