Hi Bob, Richard,
Re: IREX Page 7.2, Q19.
Airframe Icing - from page 6.15, 16 in CPL Met, my thoughts were that airframe icing can occur both within the cloud and out of the cloud, and both above and below the freezing level due to deposition on a supercooled airframe Just checking...Cheers!
Airframe icing requires the presence of supercooled liquid water droplets and sub-zero temperatures. I certainly have never heard of airframe ice occurring below the freezing level, but if you have any examples I would be interested in hearing about it and how it occurs.
Hoar frost can occur outside of cloud on descent when a 'cold soaked' airframe encounters a layer of very humid air. In that case, deposition of water vapour directly into ice covers the airframe with frost. Because it is likely to be of short duration and does not significantly change the basic shape of the aerofoil, it has much less effect on performance than rime ice or clear ice.
Rime ice or clear ice does require sub-zero temperatures and super cooled liquid water droplets. So you need to be in cloud or in freezing rain below the cloud.
