What is affected most by an aircraft being in an icing condition?

When an aircraft is in icing conditions, the most significant effects are experienced in the areas of engine performance and lift. Ice accumulation on the wings and control surfaces alters airflow, which can drastically reduce lift and increase stall speed. This can lead to a dangerous situation where the aircraft may not be able to maintain controlled flight, especially during critical phases such as takeoff and landing.

Additionally, ice can also accumulate on the engine, impacting its performance. Ice ingestion can lead to compressor stalls and a decrease in engine efficiency. This is particularly concerning as both lift and engine performance are essential for safe flight operations.

While navigation, communication, and fuel systems are important for overall aircraft functionality, they are not primarily affected by icing conditions in terms of immediate flight safety and operational capability. The physical alterations caused by icing make engine performance and lift the most critical factors to consider when dealing with icing conditions.