Unless the rain comes from convective clouds, of course…
You are saying that “convective” clouds are going to produce freezing rain. That may be true but must be a very rare case.
Peter wrote:
You are saying that “convective” clouds are going to produce freezing rain. That may be true but must be a very rare case.
No, I’m saying that they will have liquid water being brought up from lover levels above the freezing level by convection. IME you will get ice very quickly if you fly above the freezing level and enter a Cu with precipitation.,
How is this handled by big jets?
AFAIK none are certified for freezing rain.
So obviously nearly all of the time, the rain stops above the freezing level.
There may be icing conditions still but that is to be expected in IMC below 0C – that is pretty normal. But this isn’t freezing rain.
„ AFAIK none are certified for freezing rain.”
Speed. You have up to 25C difference between TAT and SAT.
So by the time you enter negative TAT you are so high that no icing (heavy) exists.
You do see rain and freezing rain quite well on the weather radar.
Freezing rain happens when 0C isotherm line becomes discontinuous and hits 1:200 0.5% gradient line that splits cold and hot from a warm front: the rain fall in warm air with high 0C isotherm and enters cold air with lower 0C isotherm…freezing rain also happens inside CB but we are talking about vertical 0C isotherm lines !
Strictly speaking, you don’t have to climb to 0C isotherm line to hit freezing rain: flying straight and level from warm side to cold side at the wrong altitude under Nimbostratus will get you the jackpot: 0C isotherm line will quickly tilt and come down under the aircraft (reverse is true 0C isotherm line go above aircraft when flying cold to warm)
I would not climb in rain under Nimbostratus or Cumulonimbus, aside from obvious dangers from turbulence, such climb is useless in my SEP: the base is usually around 5kft and the tops are usually above my personal and aircraft ceilings…in the other hand, I am happy to depart in rain and climb into low stratus or happy cruise in the rain under fluffy cumulus to wash the aircraft
Since I fly non-deiced (other than prop and pitot) to me it is all about the expected icing above 0C and being able to quickly exit it. Honestly I never considered the fact that it is raining as a determining factor: is that a big mistake?
If there is a thick temp inversion around 0C in IMC then I simply do not plan to climb through it. If it is thin or no inversion around 0C-minus10C then I will climb at a high IAS (125-130KIAS) in IMC which will give me a reduced climb rate, maybe 350-450 fpm, while watching for icing. If no icing is found then once I get to around -7C I will reduce IAS to 115 for a normal climb. If there is some icing then I immediately slow down to 110KIAS or less (Vy 100KIAS) which will give me 1000ft alt gain in 1 min then continue at 600-750fpm depending on temp and weight. Typically within 3-6 mins I am outside icing with maybe 1-2 mm accreted which sublimates once in the sunshine. If moderate or heavy icing is found (only twice in my 1400hrs flying life) then I take immediate evasive action (turn or descent, the out needs to be there) . If cloud cover is low, I also tend to zig zag in climb in 0C-minus10C to remain VMC.
My general aim is to avoid areas of high prob of icing, and go through icing layers as quickly as possible.
If convective or mountain area then I will not plan a climb through IMC above the 0C level unless it is a really thin or sparse layer.
In general I am a bit of a chicken and if expectation for my climb is cloud coverage >4 octas and icing layer thicker than 3000ft then I don’t go. Moderate or heavy icing forecast >1000ft thick with high coverage then I don’t go. For descent I am not so strict. I tend to plan descent through icing levels at high-speed though and do some pre-planning with ATC if required. I find short-term GRAMET and windy quite useful for these decisions.
If I missed your point @Peter do let me know…
There are two folds,
On the 2nd case, climbing or cruise on TKS/FIKI is not a strategy and how do you know that rain will stop when you hit negative OAT? my guess you can always climb in rain under ST/CU and you have plenty of minutes to process what is going on but one is advised to treat climbs in rain in NST/TCU as flying on clean wing: don’t overthink, turn back few seconds after it start splashing… in TCU, it’s very obvious as you start taking shower with a bucket 
