Ice warning - in VMC, below freezing level
In the thread about prop de-icing, it was commented that icing can occur anywhere, any time. On that subject, I thought my experiences from today would serve as a caution to others:
The weather was 6km vis in rain, few@2500', Bkn@4000' - distinctly VMC, although not the kind of weather that is fun to fly in.
I was planning an instrument training flight - the flight detail was to fly two instrument approaches. I expected to be cleared for the approach starting at 2000', but knew that if the airfield's overhead was not free I would need to climb to 3000'. There was a small chance of being put in the hold at 4000' if we weren't the only flight doing instrument training. So a relatively small chance of the flight entering IMC.
Bearing in mind the possibility of IMC, we began reviewing the icing conditions. There was a warm front sitting fairly stationary over the airfield. Metform 215 gave the freezing level before the front as 0', and after the front as 6000', so we figured that the actual freezing level was probably somewhere between the two.
Then we reviewed the actual weather. The temperature was +3, the dewpoint +2. I interpreted that to mean that the temperature at the cloudbase would be around about +2 degrees, still warm enough to not be a problem even if we entered IMC. But I knew I would have to be cautious about accepting a clearance to climb too high.
As we were taxying out, a Jet2 airliner was landing. I decided to take the extra precaution of asking the Jet2 pilot whether he encountered any icing on the approach, and he replied Negative. Good - I was now confident that we would be able to carry out the flight without risk of icing.
On departure, we were cleared for a standard missed approach, which consists of a climb to 2000' before making a turn back to the airfield's overhead - a procedure which would mean we maintained VMC the whole time. My student took off and put the foggles on, and then began flying the missed approach procedure.
As we levelled off at 2000' and began the turn, I noticed that the rain on part of the windscreen had stopped moving up the windscreen. I studied it a little closer, and realised that it had turned to ice....... in good(ish) VMC, well below where I expected the freezing level, and despite reports from another pilot who had just landed that he had not encountered any icing.
Needless to say, at this point I aborted the flight and we landed immediately. I am not one to mess around in ice, especially not rain-ice. I have seen ice once or twice before when I've been instructed to climb higher than the freezing level (and of course I have always descended immediately, leaving the holding area if that was necessary to avoid traffic in the descent) - but this is the first time I have ever experienced totally unexpected ice. It took me completely by surprise, and I thought others might be interested in learning from it.
Incidentally, the ice did not begin melting until we were down to 1000'. Fortunately, we were VMC at the time this occured. Had we been IMC, the lowest 10nm MSA for our airfield is 1600' which would still be in icing conditions. The first descent platform on the approach for the runway in use is also 1600', and that is to be maintained for 7nm outbound, through a base turn, and only descending below that after reaching 7nm inbound - so it would have been several minutes in rain-ice before we were able to descend out of it safely. That is quite scary!
As for the cause - it seems there was a sub-zero layer, with base of somewhere around 1000', which obviously caused the aircraft skin temperature to decrease to below freezing. No clouds formed in this layer, though, despite it being several degrees below the dewpoint.
Isn't the aim of this game to fill the bag of experience before you empty the bag of luck?????
Hope this post is useful to others, and maybe even generates some interesting debate...
FFF
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