Icing is hazardous to any aircraft, prop or jet. Here's why:

1) Weight

As ice accumulates on your aircraft, weight increase. With an increase in weight, your performance starts to dramatically decrease. Ice accumulation could even put you outside of weight and balance limitations.

2) Induction Icing

For piston aircraft, induction icing over a long period of time can lead to a decrease in horsepower. In severe cases where airflow to the engine is dramatically restricted, a complete engine failure could happen.

3) Pitot / Static Blockages

If ice forms in the pitot tube or on the static port, you can get false indications from your airspeed indicator, altimeter, and VSI.

4) Drag

When ice accumulates on your plane, large increases in parasite drag dramatically reduce your aircraft's performance.

5) Increased Stall Speed

When icing forms on the leading edge of the wing, it causes the boundary layer to separate earlier. The separation in airflow reduces lift, and increases your stall speed.

6) Reduced Visibility

A glazed over windscreen can prevent you from seeing even the most obvious features on an approach, like terrain and approach lighting.

7) Compressor Stalls

Ice on an engine inlet can cause the laminar airflow to separate, forcing the engine to ingest turbulent airflow. This puts jet engines at risk for a compressor stall.

8) Turbine Blade Damage

If you don't turn on cowl inlet anti-icing before ice starts to accumulate, ice build-up could be drawn into the engine, putting the turbine blades at risk for damage.