Carb Heat
ACA POH
Carb heat indications:
- Full hot when restarting a failed engine (2-4)
- Full hot after a partial power loss or rough running engine (2-5)
- “The carburetor/alternate air should be FULL HOT as long as suspected icing conditions exist” (2-5). This appears to refer only to the time after a gradual decrease in engine RPM
- Cold during ground operations (ensure good engine cooling and filtered air) (3-4, also see note on 6-5)
- Full hot briefly during runup (3-5)
- “Carburetor heat is available from the exhaust manifold if carburetor icing exists” (6-5)
Lycoming Operators Manual - O-235 and O-290 series
This manual has instructions for five different scenarios (3-5):
- Ground operation - limit usage of carb heat to a brief test during runup
- Take-off - full cold
- Climbing - actually pretty confusing. Mostly talks about how leaning is often required for running smoothly when the carb heat is on
- Flight operation - full cold, but if it’s ‘damp, cloudy, foggy, or hazy’, be alert for loss of power. If this happens (i.e. reduction in RPM with a fixed-pitch prop), set carb heat to hot, and fully open the throttle. This may result in an additional loss of power, which will be regained as the ice is melted out of the induction system
- Landing Approach - generally full cold. Apply full heat if icing conditions are suspected (i.e. visible moisture or high humidity)
Is carb heat absent from all the non-emergency checklists?