Aircraft Systems

Carburetor Heat Left On During Climb

FAA Ref: FAA-S-ACS-6C Area I Task G (Operation of Systems)

Scenario & Physics Summary

Applying hot, un-filtered air into the engine during takeoff or climb reduces air density, enriches the fuel-air mixture, drops manifold pressure, and significantly degrades climb performance.

Interactive 3D Visual Plates & Scenario Media

Carburettor Heat Left On During Climb Plate 1

Plate 1: Carburetor Heat Left On During Climb

Carburettor Heat Left On During Climb Plate 2

Plate 2: Carburetor Heat Left On During Climb

Carburettor Heat Left On During Climb Plate 3

Plate 3: Carburetor Heat Left On During Climb

Carburettor Heat Left On During Climb Plate 4

Plate 4: Carburetor Heat Left On During Climb

Aerodynamic & Operational Physics

Carb heat routes air over the hot exhaust muff before entering the carburetor venturi.
Hotter air is less dense (ρ = P/RT), causing a rich fuel-air mixture ratio and 3% to 15% reduction in total engine shaft horsepower.
Warm air also bypasses the induction air filter, risking dust/sand ingestion into internal cylinders.

FAA Exam Gotcha Alert

Exam Trap: Leaving carb heat ON during climb causes a unexpected drop in RPM and climb gradient. Candidates misdiagnose this as engine failure.

Frequently Asked Questions & Exam Explanations

What happens to engine power when carb heat is applied?

Engine power drops instantly because hot air is less dense, enriching the mixture and decreasing volumetric efficiency.

Is carb heat filtered air?

No. On most piston aircraft, carb heat bypasses the main air filter, taking unfiltered air directly from the exhaust shroud area.

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