ATPL MET ICING QUESTION

[AGA0001]

Good evening,

I have a question in regards to icing.
This is the information that I was given from a question.

"You are flying underneath a cloud that's producing light Drizzle. The OAT is 0 degrees Celsius. What icing, if any would be possible"

Rime Ice
Clear Ice
Mixture of Rime and Clear
None

I believe it's Clear Ice, however not 100% sure, because my assumption is that drizzle is associated with a stratiform cloud, however it will most likely form between -10 and -20

Clear ice is associated with Cumulus clouds and requires larger droplets for supercooled droplets to form. The temperature range is 0 to -15 degrees, and is why I choose this option

Could anyone please point me in the right direction.

Thank you in advance!

[megle2]

170+ looks and no one's had a crack at the correct answer
How about d ( multi choice casa exams not my best strength )

It says I'm underneath so I could be a long way below with oat well above zero degrees but then maybe I am just below and my real temp is negative

POH note - in cloud or visible moisture +5 or below ice protection on ...

[scavenger]

It says I'm underneath so I could be a long way below with oat well above zero degrees but then maybe I am just below and my real temp is negative

and

because my assumption is that drizzle is associated with a stratiform cloud, however it will most likely form between -10 and -20

This is why people run into trouble in exams - they read things into questions that are just not there. The OAT is zero and the visible moisture is drizzle.

The conditions for the formation of airframe ice are met: visible moisture (drizzle) and OAT (skin temperature) zero or less.

Drizzle consists of small droplets, so is unlikely to form clear ice because there's little release of latent heat as the droplet freezes, hence the remainder of the droplet does not remain liquid and flow back before freezing.

Only rime ice is possible.

[Runaway Gun]

Wouldn't a more relevant question, actually ask under what conditions might ANY icing be possible? It seems more practical than knowing what type.

[john_tullamarine]

It seems more practical than knowing what type.

Perhaps .. but rime is fixed easily by boots ... flow back in clear ice not so well.

[Runaway Gun]

True points JT, however I tend to avoid icing whenever possible, regardless of what types ;)

[Ascend Charlie]

The only ice that is possible for me to see is in my G&T. It doesn't say I am the pilot.

[Professional Amateur]

To answer the original question... Both may be encountered at that temp.

As for the most likely I suggest that it would be clear ice. You are at 0 OAT, that means the cloud above is below zero (only just); meaning the water droplets (be they small or large.... small in this case) are super cooled.

Drizzle hits AC, then freezes into clear ice. Temperature effects how far back the drops will extend on the AC due to freezing time.

For Rime to form it needs to me much colder.

BOM tends to agree.

[Capt Fathom]

If we assume the drizzle is a result of strato-form cloud....

The temperature within stratus is much colder than the surrounding clear air. Sometimes up to 5 degrees colder.

Something to consider.

[drpixie]

You want the CASA answer, or the real life answer - both come with plenty of wiggle room ... it is a pity that there isn't a closer match.

My guess would be CASA want you to say rime ice, because the drops are small ... but I seem to remember they were obsessed with temperature. What does the Met "blue book" say? (CASA normally want someone else to make their decision.)

My guess of the real-life answer would be none, often don't see ice collecting until a degree or two below zero. But some clouds want to make ice, and others just don't, even though conditions are apparently perfect for crustiness.

[AGA0001]

Thank you all for responding, this question appeared word for word on the exam.
The correct answer was Clear Ice! Professional Amateur - your explanation was perfect!