305 Flashcards
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
