WX 301 Final Exam UPDATED Exam
Questions and CORRECT Answers
Identify the favored regions around a winter mid-latitude cyclone for the formation of snow and
other types of frozen precipitation - CORRECT ANSWER - North west of the low/ ahead of
the warm front
Describe how the temperature must change with height to produce rain, snow, sleet, or freezing. -
CORRECT ANSWER - Depends on the thickness of the layer near the surface.
Define critical thickness - CORRECT ANSWER - Thickness you need for snow/540
decameters/5,400 meters
Analyze a 1000-500mb thickness chart to determine the likelihood of rain versus snow. -
CORRECT ANSWER - The lower the thickness, the colder the better the chances of having
snow Think 540 as 32 degrees mark bare minimum.
Define what is meant by ground icing "hold-over" times. - CORRECT ANSWER - • Hold-
over time: length of time deicing fluid will prevent ice build-up on an aircraft
• Time ranges from 45 minutes for frost to less than a couple minutes for freezing rain
Explain why equivalent liquid water precipitation rate is important in aviation winter weather
decision-making and how it affects hold-over times. - CORRECT ANSWER - • Basing
precipitation intensity on visibility alone does not adequately measure true rate of liquid water
equivalent accumulation
• Accurate, real-time measurements of liquid-equivalent snowfall rates need to be made and
reported to pilots and ground operations personnel, not just visibility measurements.
• Accurately predicting deicing hold-over times remains a significant aviation safety factor
Identify the fundamental cause of icing - CORRECT ANSWER - • Liquid water droplets +5
to -40c
, Rime ice - CORRECT ANSWER - small droplets, freeze rapidly cause trapped air, opaque
appearance, forms at temps below -15C
clear ice - CORRECT ANSWER - larger droplets with little trapped air, forms at 0 to -5 C,
equivalent to freezing rain
mixed Ice - CORRECT ANSWER - Mixed: drop size varies, forms at intermediate temps -5 to
-15C
Describe the impacts of icing on aircraft performance (stall speed, fuel consumption, service
ceiling, stall angle, etc) - CORRECT ANSWER - • Stall speed increases
• Fuel rate consumption increases
• Service ceiling decreases
• Stall at lower angle of attack than normal
• Friction increases
Describe the effects exposure time on ice buildup. - CORRECT ANSWER - • Longer
exposure time = more icing
Describe the relationship between wing size and performance degradation due to icing -
CORRECT ANSWER - Thin wings collect more ice than large wings
• A large transport aircraft will build proportionally less ice than a small aircraft going through
the same icing region
Describe super-cooled large droplets (SLDs) and runback icing as well the hazards they pose -
CORRECT ANSWER - Small ice crystals form within droplet which may cause the entire
drop to freeze
Causes a large freezing cluster of ice to form on a surface
Identify the favored areas for icing near mountains - CORRECT ANSWER - • Worst icing
near the peaks and windward side
Questions and CORRECT Answers
Identify the favored regions around a winter mid-latitude cyclone for the formation of snow and
other types of frozen precipitation - CORRECT ANSWER - North west of the low/ ahead of
the warm front
Describe how the temperature must change with height to produce rain, snow, sleet, or freezing. -
CORRECT ANSWER - Depends on the thickness of the layer near the surface.
Define critical thickness - CORRECT ANSWER - Thickness you need for snow/540
decameters/5,400 meters
Analyze a 1000-500mb thickness chart to determine the likelihood of rain versus snow. -
CORRECT ANSWER - The lower the thickness, the colder the better the chances of having
snow Think 540 as 32 degrees mark bare minimum.
Define what is meant by ground icing "hold-over" times. - CORRECT ANSWER - • Hold-
over time: length of time deicing fluid will prevent ice build-up on an aircraft
• Time ranges from 45 minutes for frost to less than a couple minutes for freezing rain
Explain why equivalent liquid water precipitation rate is important in aviation winter weather
decision-making and how it affects hold-over times. - CORRECT ANSWER - • Basing
precipitation intensity on visibility alone does not adequately measure true rate of liquid water
equivalent accumulation
• Accurate, real-time measurements of liquid-equivalent snowfall rates need to be made and
reported to pilots and ground operations personnel, not just visibility measurements.
• Accurately predicting deicing hold-over times remains a significant aviation safety factor
Identify the fundamental cause of icing - CORRECT ANSWER - • Liquid water droplets +5
to -40c
, Rime ice - CORRECT ANSWER - small droplets, freeze rapidly cause trapped air, opaque
appearance, forms at temps below -15C
clear ice - CORRECT ANSWER - larger droplets with little trapped air, forms at 0 to -5 C,
equivalent to freezing rain
mixed Ice - CORRECT ANSWER - Mixed: drop size varies, forms at intermediate temps -5 to
-15C
Describe the impacts of icing on aircraft performance (stall speed, fuel consumption, service
ceiling, stall angle, etc) - CORRECT ANSWER - • Stall speed increases
• Fuel rate consumption increases
• Service ceiling decreases
• Stall at lower angle of attack than normal
• Friction increases
Describe the effects exposure time on ice buildup. - CORRECT ANSWER - • Longer
exposure time = more icing
Describe the relationship between wing size and performance degradation due to icing -
CORRECT ANSWER - Thin wings collect more ice than large wings
• A large transport aircraft will build proportionally less ice than a small aircraft going through
the same icing region
Describe super-cooled large droplets (SLDs) and runback icing as well the hazards they pose -
CORRECT ANSWER - Small ice crystals form within droplet which may cause the entire
drop to freeze
Causes a large freezing cluster of ice to form on a surface
Identify the favored areas for icing near mountains - CORRECT ANSWER - • Worst icing
near the peaks and windward side
