_____ blocks airflow to the engine(s), which can degrade engine performance or cause failure.

Induction icing is the phenomenon where ice forms in the engine's induction system, specifically in the air intake or in the manifolds. This ice can accumulate and block airflow, which reduces the engine's ability to draw in air necessary for the combustion process. Consequently, when the airflow is restricted, engine performance can degrade significantly; in extreme cases, it can lead to engine failure. It's crucial for pilots to understand the conditions in which induction icing occurs, especially during flight in cold and humid environments.

Structural icing and frost accumulation pertain to ice forming on the airframe of the aircraft and can affect aerodynamics and control, but they do not specifically block airflow to the engine like induction icing does. Fuel contamination involves impurities in the fuel that can affect the combustion process but does not directly relate to airflow into the engine.