deice,
I can see your point.
However, fly in level flight at FL70 in stratus with OAT-5 on a certain day and you don't get ice. Do it again the next day (or even a few hours later) and you pick up ice.
Ice is so unpredictable that unless the previous pilot has reported ice at your level recently then there is very little to go on. Most icing forecasts are based on the probability of icing being in any cloud at sub zero temperatures and the fact that icing in convective situations is more serious i.e. cu family and over rising terrain.
So in your aircraft that is not approved for flight in icing conditions, you can indeed stay on the ground or limit yourself to VMC below cloud flying. However, you will find that you will cancel many flights that could have been safely completed.
If you are flying in visible moisture and you start picking up ice, the only answer is to exit icing straight away. The question is do you go up or go down. Icing is normally found in 3000ft bands so if you are 1000ft into the band when you see ice forming, is it quicker to climb above or descend below the icing layer?
You would only be illegal if you had to descend below MSA to clear the ice or you remained in icing conditions i.e. you continue to pick up ice.
Most IR candidates will be familiar with the pre-takeoff brief that they give the examminer. It goes along the lines of;
..........If we encounter icing conditions I will climb above or descend below icing but not below MSA and then decide to continue or divert............
The IR test is asumed to be in icing conditions and many people manage to pass in aircraft with no approval for icing conditions because they will comply with the above statement.
As soon as IMC is simulated on the test i.e. at 300ft the first thing the candidate is expected to say is "icing check".
Unfortunately, airframe icing is often glossed over on the IMC course and thus there is a widespread misunderstanding.
Complete the NASA course I gave the link to above and while it is designed for people who fly aircraft which are approved for flight in icing conditions, it is useful for everyone.
Finally note that most light twins are only approved for flight in light icing conditions. Light icing is defined as;
“Light — The rate of accumulation may create a problem
if flight is prolonged in this environment (over one hour).
Occasional use of deicing/anti-icing equipment removes/
prevents accumulation. It does not present a problem if
the deicing/anti-icing equipment is used;
Regards,
DFC