On Dec 2, 7:14 am, Jeffrey Bloss wrote:
On Tue, 1 Dec 2009 18:47:43 -0800 (PST),
wrote:

As for the most common causes of engine failure, fuel starvation
is the second most common. Carburetor ice is the most common, by a
wide margin. There's far too little training given on the phenomenon.

Dan

What training I received was mainly about how to detect it not how to
prevent it, what conditions, what cloud formations, etc etc...that all
became self-help and assistance from other pilots.

And here's classic proof that the training and understanding is
deficient: That carb ice occurs only in or around clouds.

Carb ice is a threat anytime there's enough humidity and the
temperature is below 100°F. It can occur on a warm summer day. It can
occur on a cool day. It can occur on winter days when the temperature
is around 0°F. Water can exist as a liquid down to -20°C (-6°F? or
so?). The key is the distance between temperature and dewpoint: the
closer they are, the larger the likelyhood of carb ice. Checking temp
and dewpoint should be mandatory before flight but that sort of
training is rare.

And then we hear of accidents where the RPM was dropping so the
pilot pulled the carb heat, buit them the engine ran rough so they
pushed it off again. So the engine iced up and quit. Carb ice melts
into water when it's heated, and the engine runs sorta rough on water,
see, so you need to leave that carb heat on until things sort
themselves out. Sometimes the ice develops to the point that the power
drops off so far that there's no more heat in the exhaust and so no
carb heat. The airplane is doomed at that point.

The mechanics of carb ice are too little understood. The venturi
causes a pressure drop in the carb, which causes a temperature drop.
The fuel vaporizing in the carb throat absorbs heat from the air as it
evaporates, cooling things even further. The temp drop can be as large
as 70°F; add that to the freezing point of 32, and we get 102°.

Googling "carburetor ice" brings up lots of good stuff.

Dan

Dan