Lesson 13 Flashcards
The four types of icing are?
Hoar frost
Clear ice
Rime ice
Mixed ice
Describe hoar frost
** Usually occurs on the ground ** Hoar frost is a greyish-white, feathery, crystalline formation that can cover the entire surface of
an aircraft. It is the same as the ice that forms on cars on cold winter nights.
Hoar frost is not usually an issue for aircraft because it is very thin and easily removed.
Describe Clear Ice
** most dangerous ** BIG DROPS *** Clear ice is a clear, glassy, hard ice that forms on the leading edges of the wings and spreads
back over the wing surfaces when the air temperature is between 0˚C and -10˚C.
This type of ice is found in freezing precipitation and in supercooled rain in clouds.
Clear ice is denser and more homogenous than rime ice and is very dangerous for aircraft.
It can:
* Change the shape of the wing leading to a reduction in lift
* Increase the weight of the aircraft resulting in a higher stall speed
* Block the pilot’s view
It is very difficult to remove clear ice.
Describe Rime Ice
small drops Rime ice is an opaque, whitish, pebbly, granular type of ice that forms on the leading edges of
the wings but does not spread back over the wing surfaces.
It forms when the air temperature is between -15˚C and -20˚C and is the same as the ice you
find in a freezer.
Rime ice accumulates much more slowly than clear ice. The accumulation of rime ice on the
leading edges of the wings can disturb the flow air over the wings and affect lift.
Rime ice is primarily supercooled cloud droplets and therefore can only be encountered while
flying in clouds. It is not as difficult to remove as clear ice.
Describe mixed ice
Mixed ice is a mixture of clear and rime ice. It is most likely to form in temperatures between -10°C and -15°C.
The result is an ice coating that is weaker than clear ice but stronger than rime ice.
It can:
* Lead to a reduction in lift
* Increase the weight of the aircraft
* Significantly reduce visibility
There are 4 intensities of icing. What are they?
Icing may be described as trace, light, moderate, or severe.
Describe trace icing
** Accumulation rate is less than ¼ inch per hour on the outer wing **
* Ice first becomes noticeable
* Not a problem for aircraft
* Pilot should consider exiting icing before it worsens
Describe light icing
** Accumulation rate is ¼ to 1 inch per hour*
* Occasional cycling of manual de-icing systems to minimize ice accretion
on airframe
* Not normally a problem unless the aircraft is exposed for a lengthy
period of time
* Pilot should consider exiting icing
Describe moderate icing
- Accumulation rate is 1 to 3 inches per hour
- May lead to a potentially hazardous icing situation
- Pilot should consider exiting icing as soon as possible
- Diversion might be required to get out of the icing situation
Describe Severe icing
- Accumulation of more than 3 inches per hour
- Occurs when the rate of accumulation is not reduced or controlled by
anti-icing and de-icing systems - Ice accumulates in locations not normally prone to icing
- Immediate exit from icing is necessary by means of a change in heading
or altitude
There are two requirements for ice to form on an aircraft while it is in flight. What are they?
First, the aircraft must be flying through visible water in the form of rain or cloud droplets.
Second, when the water droplets strike a surface, their temperature or the temperature of the
surface must be 0°C or below.
In what temperature range will the heaviest icing usually occur?
The heaviest icing usually occurs in the range from -10°C to 0°C when supercooled water
droplets freeze on impact and adhere to the plane.
Generally, high-performance aircraft collect _____ ice than low-performance aircraft in the same amount of time because they have _____ wing profiles
Generally, high-performance aircraft collect more ice than low-performance aircraft in the same amount of time because they have thin wing profiles
There are other variables that determine where and how much ice an aircraft will pick up,
including: (5 answers)
- Speed of the aircraft
- Shape of the airfoil
- Type of cloud encountered
- Type of ice encountered
- Length of time in the icing conditions
What clouds are responsible for the heaviest icing potential?
CU, TCU, and CB clouds produce the heaviest icing potential. This is due to fast vertical velocities that lead to bigger droplets.
