The Piper M350: Dealing with Airfame Ice and Rainshowers

[@kevinm2099]

Why do you have alternate air open in visible moisture even with warm temps aloft and should I be doing that with my PA32 ?

[@RWRPilotTraining]

Hi Kevin, Alternate induction air is designed to prevent damage to turbochargers or even an engine stoppage due to ice in the air intake plenum behind the air filter. Your question is one of basic physics. Remember, when air goes thru a venturi (the air filter and plenum) it cools adiabatically. Sometimes this cooling is just enough to produce ice in the plenum even when the air temperatures are above freezing. Air in the area behind the filter flows unimpeded through the turbocharger blades where it is compressed, cooled and fed to the cylinders. If there is ice in this flow it can damage the turbocharger blades. If there is enough ice it can cause the engine to fail. For this reason most POHs call for opening the alternate induction air whenever you are planning to enter visible moisture of any kind (snow Ice rain .. clouds etc). You should consider leaving alternate induction air open until you are safely on the ground. As for your POH? .. check it out; and ask your flight instructor. Fly Safely - Train Often .. DR

[@bg-balajiprasad9088]

I was flying FL 230 yesterday, it was a beautiful day with SKC and no visible moisture, my OAT was -27 and I had windshield frost on the cabin side and I used defrost air to melt it but it took a while, so I need to switch to alternate air in this condition, PA46 Malibu Mirage

[@RWRPilotTraining]

No. What you were experiencing was condensate on the inside of a cold window created from water vapor inside the cockpit from breathing and perspiration which does freeze, however it did not come from outside. The best way to get rid of the is with the defroster on high and ECS (bleed air) on high if you are in a turboprop. The air outside on a clear day is very dry at that altitude and will likely sublimate the ice on the inside very quickly. If not consider the windshield heat on low as well. Alternate induction air (in a turbocharged piston engine) helps avoid ice in the intake plenum which can form as a result of adiabatic cooling associated with a pressure drop across the primary intake filter. This is a somewhat poorly understood concept so be sure you understand it thoroughly. Fly Safely - Train Often .. DR