once over the rockies in a l4p IMC there was a loud ZITTTT and it was like someone
turned the lights off it got so dark so fast with the instant load of ice...
on came the alt air light meaning the spring door opened letting DRY air
in the engine.. even after all the ice had departed the aircraft, the alt
air light was still on, more do to the airflow a 550 can pump than
a wet/iced filter.

> consider the ram air as the "alternate" air source during any engine difficulty.

I'm not so sure that's a source of DRY air... I have three sources
of air: filtered, spring bypass, and ram... and my filter is
still too small because I see such a large delta with ram..
http://lancairlegacy.com/Mahar_images/airbox_lrg.jpg

I turn off ram any time the peto heat is on... there is
too much stuff for ice to stick to, and I would never be
able to close the door once ice forms.

as George points out, in certified installs the FAA requires
hot alt air... the cuff on this alt air input is near the hot eshoust
http://rob.com/lancair/Others/NorthCoast/north.jpg

> Wrong-o, full rich and still hot,
I think Walter was trying to say if the CHTs go up you might
need to "re-peak" as the amount of air has changed..

a good example of this is when I turn on ram after peaking
filtered air... there is way too much ram air and the engine
falters noticeably until I give it more gas..

> Mooney engineer told me "Don't use the ram
> air on a fuel injected engine".

ram air is a good thing as long as you keep positive
pressure to the injectors
http://lancair.net/lists/lml/Message/23078.html

thanks for shairing... the more we think, the more we understand.