4I Emergencies - Icing Flashcards
- Name the three types of structural ice that may occur in flight. (AC 00-6A)
Clear ice—forms after initial impact when the remaining liquid portion of the drop flows out over the aircraft surface, gradually freezing as a smooth sheet of solid ice.
Rime ice—forms when drops are small, such as those in stratified clouds or light drizzle. The liquid portion remaining after initial impact freezes rapidly before the drop has time to spread out over the aircraft surface.
Mixed ice—forms when drops vary in size or when liquid drops are intermingled with snow or ice particles. The ice particles become imbedded in clear ice, building a very rough accumulation.
- What are the three main types of aircraft icing? (AC 00-6A)
Structural, induction system, and instrument icing
- What is necessary for structural icing to occur? (AC 00-6A)
The aircraft must be flying through visible water such as rain or cloud droplets; temperature must be at the point where moisture strikes the aircraft at 0°C or colder.
- Which type of structural icing is more dangerous, rime or clear? (AC 00-6A)
Clear ice is hard, heavy, and tenacious. It is typically the most hazardous ice encountered. Clear ice forms when, after initial impact, the remaining liquid portion of the drop flows out over the aircraft surface, gradually freezing as a smooth sheet of solid ice. This type forms when drops are large, as in rain or in cumuliform clouds. Its removal by deicing equipment is especially difficult due to the fact that it forms as it flows away from the deicing equipment (inflatable boots, etc.).
- During your preflight planning, what type of meteorological information should you be aware of with respect to icing? (AC 91-74)
a. Location of fronts—the front’s location, type, speed, and direction of movement.
b. Cloud layers—the location of cloud bases and tops; this is valuable when determining if you will be able to climb above icing layers or descend beneath those layers into warmer air; reference PIREPS and area forecasts.
c. Freezing level(s)—important when determining how to avoid icing and how to exit icing conditions if accidentally encountered.
d. Air temperature and pressure—icing tends to be found in low-pressure areas and at temperatures at or around freezing.
- What is the definition of the term “freezing level” and how can you determine where that level is? (AC 00-6A)
The freezing level is the lowest altitude in the atmosphere over a given location at which the air temperature reaches 0°C. It is possible to have multiple freezing layers when a temperature inversion occurs above the defined freezing level. A pilot can use current icing products (CIP) and forecast icing products (FIP), as well as the freezing level graphics chart to determine the approximate freezing level. Other potential sources of icing information are: area forecasts, PIREPS, AIRMETs, SIGMETs, surface analysis charts, low-level significant weather charts, and winds and temperatures aloft (for air temperature at altitude).
- What action is recommended if you inadvertently encounter icing conditions? (AC 00-6A)
You should leave the area of visible moisture. This might mean descending to an altitude below the cloud bases, climbing to an altitude above the cloud tops, or turning to a different course. If unable to leave the area of visible moisture, the pilot must move to an altitude where the temperature is above freezing. If you’re going to climb, do so quickly; procrastination may leave you with too much ice. If you’re going to descend, you must know the temperature of the air and the type of terrain below.
- AIRPLANE ONLY*
8. If icing has been inadvertently encountered, how would your landing approach procedure be different?
The following guidelines may be used when flying an airplane which has accumulated ice:
a. Maintain more power during the approach than normal.
b. Maintain a higher airspeed than normal.
c. Expect a higher stall speed than normal.
d. Expect a longer landing roll than normal.
e. A “no flaps” approach is recommended.
f. Maintain a consistently higher altitude than normal.
g. Avoid a missed approach (get it right the first time).
- Which type of precipitation will produce the most hazardous icing conditions?
Freezing rain produces the most hazardous icing conditions.
- Does the stall warning system have any protection from ice? (POH)
No, but some aircraft may be equipped with a heated stall warning system which consists of a vane, sensor unit and heating element on the leading edge of the wing. Usually this system is activated by the same switch that controls the pitot heat.
- What causes carburetor icing and what are the first indications of its presence? (FAA-H-8083-25)
The vaporization of fuel, combined with the expansion of air as it passes through the carburetor, causes a sudden cooling of the mixture. The temperature of the air passing through the carburetor may drop as much as 60°F within a fraction of a second. Water vapor is squeezed out by this cooling, and, if the temperature in the carburetor reaches 32°F or below, the moisture will be deposited as frost or ice inside the carburetor.
For airplanes with a fixed pitch propeller, the first indication of carburetor icing is a loss of rpm. For airplanes with controllable-pitch (constant speed) propellers, the first indication is usually a drop in manifold pressure.
- What conditions are favorable for carburetor icing? (FAA-H-8083-25)
Carburetor ice is most likely to occur when temperatures are below 70°F (21°C) and the relative humidity is above 80 percent. However, due to the sudden cooling that takes place in the carburetor, icing can occur even with temperatures as high as 100°F (38°C) and humidity as low as 50 percent. This temperature drop can be as much as 60 to 70°F. Therefore, at an outside air temperature of 100°F, a temperature drop of 70°F results in an air temperature in the carburetor of 30°F.
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AIRPLANE ONLY*
13. If an airplane has anti-icing and/or deicing equipment installed, can it be flown into icing conditions? (FAA-H-8083-3)
The presence of anti-icing and deicing equipment does not necessarily mean that an airplane is approved for flight in icing conditions. The AFM/POH, placards, and manufacturer should be consulted for specific determination of approvals and limitations.
- A pilot flying an aircraft certificated for flight in known icing (FIKI) should be aware of a phenomenon known as “roll upset.” What is roll upset? (FAA-H-8083-15)
Roll upset is an uncommanded and uncontrolled roll phenomenon associated with severe in-flight icing.
It can occur without the usual symptoms of ice accumulation or a perceived aerodynamic stall.
Pilots flying certificated FIKI aircraft should be aware that severe icing is a condition outside of the aircraft’s certification icing envelope. The roll upset that occurs may be caused by airflow separation (aerodynamic stall), which induces self-deflection of the ailerons and loss of or degraded roll handling characteristics. The aileron deflection may be caused by ice accumulating in a sensitive area of the wing aft of the deicing boots.
- AIRPLANE ONLY*
15. What is the recommended recovery procedure for a roll upset? (AC 91-51)
a. Reduce the angle of attack by increasing airspeed. If in a turn, roll wings level.
b. Set appropriate power and monitor the airspeed and angle of attack. A controlled descent is a vastly better alternative than an uncontrolled descent.
c. If flaps are extended, do not retract them unless it can be determined that the upper surface of the airfoil is clear of ice, because retracting the flaps will increase the AOA at a given airspeed.
d. Verify that wing ice protection is functioning normally by visual observation of the left and right wing.
