Posted for "George Braly" <gwbraly@gami.com>:


Larry, If you can only get 20" MP in icing conditions,  then, bluntly,  the installation is not one that I would consider "airworthy" for anything other than pure VFR flight in the warmer seasons.

This is an unacceptable situation for an aircraft designed to fly in the flight levels.

So, the problem REALLY needs to be addressed.   My first exposure to this problem was in 1993 on an acceptance flight where an alternate air door "froze" closed at 17000 feet over the rockies.  Engine quit.  Not a good situation.

Since then, I have designed, test flown, and certified at least three different versions of alternate air systems - - and I am pretty sure that the restricted air inlet/warm air is not the primary problem.  THEY ARE or CAN BE PROBLEMS at high altitude,  but it would take a really terrible ALT AIR system to cause that much of a problem at lower altitudes.  Some basic testing is in order.  I am rather surprised that it has not already been done!

Regards,  George