TThierry, there is a problem with the FAA diagram in your first post. It shows 100% humidity as dewpoint being 10 C above ambient temp, which of course is nonsense. So that one is NOT to believe.
You're right. But this chart has been used by the FAA for years. Difficult to think they made such a mistake and that moreover noone noticed. Isn't there an explanation?
Difficult to think they made such a mistake and that moreover noone noticed. Isn't there an explanation?
Perhaps it is that nobody actually looks at the axes on the graph. If you don't read the numbers, there is nothing wrong with it 
I'm gonna try and contact them to see what they say. I'll keep you posted if they answer.
Here is the answer I got from the FAA:
The chart listed in the "faasafety" website does not make sense. Its possible that someone may have made a mistake and mislabeld the x-axis on the chart. I will try and contact someone in that FAA organization and see if they can make the correction. However a colleague was able to locate a chart published in an FAA Special Airworthiness Information Bulletin #SAIB CE-09-35 which corresponds to the "bea" chart.
I'll let you know when I get something new.
Meanwhile only the french BEA chart is to be used.
In most (all?) fuel injected installations, the air passes through a filter and one would expect supercooled water droplets to be freezing up when they hit that, not passing through it untouched and then freezing inside the fuel servo.
If there are supercooled droplets you would have other issues as well. The engine is the least problem you have. I had them once in my life below clouds and I do not want to repeat that ever again. The rate of picking up airframe ice is unbelievable.
I recall a pretty accurate observation about carb ice by my met instructor years ´n years ago who said that in our hemisphere (pretty much all of Europe north of the alps and most south of it too) carb ice conditions exist 24 hours a day 365 days a year.
I reckon he has a point.
With my old Cessna 150 I experienced carb ice in conditions which I would have thought without a problem and had none where I´d have expected them. Then I bought a carb temp gauge and immediately understood a lot more about it. The regimes and temperatures inside the carburettor do not really correspond to the school thinking that carb ice would be most prominent in descent and approach. Temperatures during reduced engine power on the O200 were almost always outside carb ice range whereas they sank dramatically while on higher power. Consequently, I was no longer wondering why the only carb ice event when my engine nearly stopped but was resolved immediately by pulling heat was at FL075 with blue skies and full open throttle.
With all the garbage we are supposed to carry on our planes, I wonder why carb temp gauges are not encouraged with the airplanes who need them. I am currently looking for a way to getting one into my overstuffed panel and would do so gladly tomorrow if I could figure out where to put it.
The O360 in the Mooney is notorious for carb icing and i have had several events on the ground primarily. Doing a carb ice check before take off is therefore very much recommended...
Considering the fact that a carburettor will cool the air by close to 20 deg C at average power and closer to 30 degrees C at max power, it will place the carburettor temperature in the icing range almost always.
Therefore the graphs posted are useful but they should not be the final word. Airmanship, listening to your engine and reckognizing the signs (MP/RPM drop at constant altitude and pitch/power, rough running e.t.c.) are required if you don´t have a gauge, keeping the temps outside whenever there is any doubt is the option if you have one.
Therefore the graphs posted are useful but they should not be the final word.
I know several pilots who do not use the carb heater when the outside temperature is "warm", i.e. in summer. However the graph shows that carb icing is possible up to 30°C. The graph should be used to warn that even when it is "warm", icing is possible.
Thanks TThierry for coming back with an faa answer. I guess the fact that the chart appears to have been used widely without being corrected suggests that it is not often used for checking carb ice risk specifically.
I have experienced carb ice in all seasons except freezing winter. Never at full or climb power; once with cruise power (just below a cumulus cloud); a couple of times during approach, and many times on the ground shortly after engine start. I had it once on an ILS in IMC - being used to injected engines at the time I forgot the carb heat in the Piper Dakota. When I set the mixture to full rich shortly before minimums the engine almost quit. I re-leaned, applied carb heat, and landed. I still wonder if I could have made a go-around.
I had carb icing last Saturday, idling in about +5 degrees and high humidity. Carb heat solved it in a second.
