Wx Hazards Flashcards
Where is the stable air and the turbulence associated with fair Wx cumulus clouds?
Fair Wx cumulus clouds form at the top of up drafts
What are the 2 types of convective currents?
Up drafts
Down drafts
Name 3 obstructions to wind flow that can cause mechanical turbulence?
Buildings
Trees
Mountains
Definition of wind shear
Change in direction and/or speed with altitude or horizontal distance
What are the 5 possible causes of wind shear?
Obstructions to wind flow Surface friction Frontal zones Above stable layers and inversions Down drafts and microbursts
What is a microburst?
Precipitation induced down drafts
What are the hazards associated with a microburst?
Can cause tornado like damage
What are the 2 steps to take if a pilot encounters a microburst?
Apply takeoff power and climb at best climb speed
Where is clear air turbulence usually located?
At high altitudes near the tropopause
Describe light turbulence?
Momentary, slight, erratic changes in altitude and/or airspeed slight strains against the seatbelt
Describe moderate turbulence
Change in attitude and/or altitude, able to maintain positive control definite strains against seat belts
Describe severe turbulence
Large abrupt changes in attitude or altitude, momentary loss of control, forced violently against seat belts
Describe extreme turbulence
Aircraft tossed about, virtually impossible to control
What causes mountain wave turbulence?
Wind over mountainous areas causes wave like winds on the lee side
What are the 3 types of clouds that may occur with mountain wave turbulence?
Cap clouds
Rotor clouds
Lenticular clouds
Where is the turbulence in mountain wave turbulence?
Severe turbulence can be encountered on the leeward side
Turbulence can be encountered up to 3,000 ft above the mountain
What are the 3 conditions necessary to form thunderstorms?
Sufficient moisture
Unstable air
Lifting mechanism
3 stages of a thunderstorm
Cumulus
Mature
Dissipating
What 3 things happen during the cumulus stage of a thunderstorm?
- lifting can exceed 3,000 ft/min vertical development
- small raindrops are lifted above the freezing level posing an icing hazard
- raindrops grow in size and eventually begin to fall creating a downdraft
What 7 things happen during the mature stage of a thunderstorm?
- precipitation begins to fall from the base
- downdraft may exceed 2,500 ft/min
- updrafts can exceed 6,000 ft/min
- anvil forms when rising air reaches tropopause
- gust front at surface
- surface pressure rises and temp drops due to downdraft
- thunderstorm reaches it’s greatest intensity
What 3 things happen during the dissipating stage of a thunderstorm?
Downdrafts greater than updrafts
Precipitation at the surface
Without updrafts providing moisture, thunderstorm begins to collapse
What are the 2 characteristics of an air mass or single cell thunderstorm?
Not associated with any frontal Wx
Typically lasts up to an hour
Where are embedded thunderstorms located?
Thunderstorms hidden in the clouds
What are the 2 characteristics of a multicellular thunderstorm?
Long duration due to multiple cell formation
Gust front drives formation of new cells
What are the 8 hazards of thunderstorms?
Tornadoes Squall lines Turbulence Icing Hail Low ceilings Low visibility Lightning
6 characteristics of a supercell thunderstorms
Can last over 2 hours
May split
Common in Midwest
Tornadoes
Has multiple cll structure but in different formation than multicell
Rotational formation due to differing surface winds and
3 characteristics that define a severe thunderstorm
Wind gusts of 50 knots or more
Hail 3/4 inch or larger in diameter
Strong tornadoes
What is the minimum recommended distance to stay away from thunderstorms?
20 miles
What are 4 cloud types that could identify a severe thunderstorm?
Shelf or roll clouds
Dark color clouds
Mammatus clouds
Towering cumulus clouds
What is structural icing?
Ice which forms on aircraft
What temp range is conducive to clear ice formation?
0 to -5 degrees Celsius
Where does clear ice come from
Drops from rain or cumulus cloud
What does clear ice look like?
Solid clear appearance, child
Where on an airfoil does clear ice strike
Past the leading edge!
Yarrrr
What can cause structural icing to occur in ambient temperatures that are slightly above freezing?
Low pressure over airfoils may drop temperatures to freezing.
List the eight adverse effects of structural icing?
reduced lift Decreased thrust Increased weight Increased drag Impairs engine performance False instrument indications Loss of radio communications Loss of operation of control surfaces, landing gear, hinges.
At what distance separating strong or very strong radar echoes can a flight path be considered free of severe turbulence?
20-30 miles
Do METAR reports include a descriptor for severe thunderstorms?
No.
What temp range is conducive to rime ice formation?
-15 to -20
Where does rime ice come from?
Drops from drizzle or stratus clouds
What does rime ice look like?
White, brittle, rough, light
Where on an airfoil does rime ice stick?
Leading edge
What temp range is conducive to mixed ice formation?
-5 to -15 degrees Celsius
What does mixed ice look like?
Very rough often growing out wards
Both clear and rime ice characteristics
What 3 conditions must exist for structural icing to occur?
Visible moisture
Supercooled droplets
Freezing temps
What is in the visible moisture that actually sticks to the structure of the helicopter?
Water or supercooled droplets (the moisture)
Why should a pilot not attempt to fly under a thunderstorm even if you can see through to the other side?
Turbulence and wind sheer under the storm could be disastrous.
