Freezing Levels

[Kirstey]

I should probably know this - but this is the 1st time it's potentially been an issue for me.

If I fly an aircraft that is not cleared for icing conditions ie a PA28-161, does this mean I need to remain below the freezing level? or do i just need to be very cautious above the freezing level?

ta

[rustle]

You can climb above the freezing level, but not through any visible moisture (cloud/fog/rain/snow etc).

It's not the temp that weighs you down, it's the frozen moisture :)

Some of the best, smoothest, clearest flying is when the ground temp is 0 and it's VMC...

HTH

[ratsarrse]

Some of the best, smoothest, clearest flying is when the ground temp is 0 and it's VMC

Went flying yesterday - mostly clear skies apart from a big lump that rolled in from the east, temp 1c. I was expecting smooth air, but there were quite a few bumps. Not very good at this met stuff and I couldn't work out why it would be a bit bumpy. Anyone care to enlighten me?

[khorne]

It is obviously true that you need moisture for ice but it does not have to be above the freezing layer. If your temperature gauge is showing a very low temperature but not quite freezing, say 2 degrees, then you can still get ice. When it gets very cold and high you tend not to pick up ice even in cloud but that also depends on the cloud.

You can also pick up ice hitting freezing rain which has happended to me once and I do not care to repeat it. This was also slightly above zero but the airframe was still very cold from a descent.

Just because an aircraft is "Cleared for known icing" does not mean that it is a good idea. Small amounts of ice from passing through cloud layers to get on top in a non de-iced aircraft can be acceptable to many people whereas severe icing to a de-iced aircraft can still be very serious.

[ShyTorque]

RatsA,

It was the instability of the air that caused the bumps. Hence the snow showers.

Kirstey,

There are two separate icing problems that may affect your aircraft. The first is airframe icing. If your airframe is at or colder than 0 degrees C then just like a car or anything else outside in such condititions, it may get ice on it if there is moisture in the air you fly through.

Bear in kind that it is possible for unfrozen moisture to exist below zero celsius (supercooled moisture). If it does, it's just waiting for your aircraft to come along to form a nucleus to freeze onto. It may affect the aerodynamics of the wings in particular, also your personal visibility through the transparencies, performance of the radio aerials, movement of the flying controls / flaps, undercarriage retraction and extension and braking systems. All not nice.

Over and above that, your engine has a carburettor with a venturi and evaporating petrol inside which causes a marked reduction in temperature within it. With an outside air temperature well above zero (actually to about plus 10C or higher ), you may still be getting carburettor ice forming. Remember to use carb. heat as recommended by the Flight Manual for your aircraft. This might be required in summer as well as now, depending on aircraft type.

Climbing through a layer of cold cloud can be OK if you are absolutely sure it is only a very thin layer and there is clear air above. Unfortunately, cloud has a nasty habit of thickening up once you are above it. To come down again you need a reduced throttle setting and this is when your carb is most likely to suffer from icing as the internal depression is highest.

The best advice is to stay below the zero degree level and stay on the ground if you aren't sure.

[Kirstey]

Cheers for everyone's help on this. I'm much clearer on the carb icing issue. Although I'm through the solo student - low hours ppl stage of carbheat every 10 seconds!

I guess the trick with airframe icing is to fly with a good difference between temp/dp and to stay clear of any moisture. I guess the effects of airframe icing are very noticable very quickly!?

anyway thanks again for the help.

K