Icing

Question 1

In which temperature range can the greatest concentration of SCWD be found in a cloud?

Answer 1

0°C to -10°C.

Question 2

What are the hazards of flying in icing conditions?

Answer 2

The accumulation of ice on the aircraft can lead to:

» increased aircraft mass and drag

» disruption of airflow over aerofoils

» classic piston engines: carburettor icing

» turbine engines: reduction in the air intake diameter

» jamming of the control surfaces

» windscreen icing

Question 3

When does hoar frost form?

Answer 3

If the aircraft is flown from cold air to warm air of high humidity (deposition).

It can also accumulate overnight on the ground.

Question 4

Define: freezing rain.

Answer 4

Rain that freezes as it falls.

It forms in an inversion of temperature where it falls from a level above 0°C to a level below 0°C.

Question 5

What affects the size of SCWD?

Answer 5

Vertical depth of ascending air in a cloud (more collisions = larger droplets).

Question 6

Describe: rime ice.

Answer 6

Opaque and brittle. Forms quickly.

Question 7

How can we estimate ram rise with a formula?

Answer 7

RR = (TAS/100)²

Question 8

Which service provides information on likelihood of carburettor icing on a given day?

Answer 8

No service provides such information. Pilots must use their knowledge and experience to assess the risk.

Question 9

What’s the relationship between temperature and dew point?

Answer 9

The closer the temperature and dew point, the higher the relative humidity.

Question 10

On which days will chances of carburettor icing be higher:

(a) on cold and dry winter days

(b) on warm and humid summer days

?

Answer 10

On warm and humid summer days, because of the higher water vapour content of the air.

Question 11

When can airframe icing be experienced?

Answer 11

Whenever an aircraft flies through clouds or precipitation at negative temperatures.

Question 12

Before flight, if we want to assess the possibility of carburettor icing, we need information on RH (from dew point). What if such information is not available to us?

Answer 12

We assume a high RH.

Question 13

By which processes may ice form on the aircraft?

Answer 13

Deposition and freezing.

Question 14

Should encounters with icing conditions be reported to ATS?

Answer 14

Yes.

Question 15

Are engines with fuel injection system prone to carburettor icing?

Answer 15

No, because fuel is delivered to cylinders directly.

Question 16

Define: ram rise.

Answer 16

Heating of the airframe due to airflow compression and friction.

Question 17

What is another name for intake ice?

Answer 17

Impact ice.

Question 18

Describe: hoar frost.

Answer 18

Light and brittle.

Question 19

In which conditions will ice form in turbine engine intakes?

Answer 19

In the same conditions that produce airframe icing, and additionally at high power settings at low speeds.

Question 20

Why is freezing rain particularly dangerous?

Answer 20

Because it can fall onto all the exposed upper surfaces of the airframe, not just the leading edges.

Question 21

List the icing intensity criteria for reporting.

Answer 21

Trace: perceptible but not hazardous

Light: not hazardous unless present for more than an hour, occasional AI/DI prevents any problems

Moderate: potentially hazardous, AI/DI is necessary

Severe: hazardous, AI/DI is of no use

Question 22

Can clear ice occur on the airframe if the water droplet temperature is above 0°C?

Answer 22

If the airframe temperature is below 0°C, yes.

Question 23

When can impact ice form?

Answer 23

In clouds or precipitation when the temperature of the aircraft or the precipitation is below 0°C.

Question 24

What’s a common cause of carburettor icing?

Answer 24

A combination of the reduced temperature and pressure caused by low power settings in conditions of high humidity.

Question 25

Describe: clear ice.

Answer 25

Transparent and heavy. Forms slowly.

Question 26

When does rime ice form?

Answer 26

When small SCWD come into contact with the airframe that had been cooled to below 0°C.

At ground level, it may form in freezing fog.

Question 27

When does clear ice form?

Answer 27

When large SCWD come into contact with the airframe that had been cooled to below 0°C.

Question 28

What is another name for clear ice?

Answer 28

Glaze ice.

Question 29

What are the main types of induction system icing in piston engines?

Answer 29

» Carburettor icing

» Fuel icing

» Intake icing

Question 30

Which form of ice is the most dangerous and why?

Answer 30

Clear ice, because:

» it is the heaviest form

» it affects a large area

» it is difficult to remove

» it is difficult to detect

Question 31

Define: intake ice.

Answer 31

Ice which builds up on air intakes, filters, valves, etc.

Question 32

What’s the significance of dew point being equal to temperature?

Answer 32

RH reaches 100% and fog/clouds may form.

Question 33

Which atmospheric conditions are most conductive to carburettor icing?

Answer 33

High RH with temperatures of -10°C to +25°C.