The Power Thief in Marginal Conditions: Engine Icing in Light Aircraft
Engine icing in UK GA rarely looks dramatic. It tends to show up in the sort of weather many of us fly in regularly: low cloud, mist, drizzle and high humidity. Its effects are gradual and technical, which makes it easy to overlook, particularly when conditions feel fairly benign rather than obviously hostile.
UK weather is especially good at producing engine icing because it so often combines moisture, small temperature spreads, and long periods at reduced power. Extended descents, circuit flying, or even ground operations in damp air can all provide the time and conditions needed for ice to form inside the engine rather than on the airframe.
So what’s actually happening inside the engine?
❄️ Air intake & filter
Ice can form at the air intake or filter in freezing fog, rain or slush. As airflow is restricted, available engine power reduces. This can start on the ground during taxi or power checks, not just in flight, and is sometimes mistaken for the engine simply not being fully warmed up.
❄️ Carburettor
Within the carburettor, the venturi effect and fuel vaporisation cause a significant temperature drop. Ice builds on the throttle butterfly, gradually restricting airflow. When carb heat is selected, it’s normal to see a further short-term reduction in power as warmer, less dense air enters and any accumulated ice begins to melt. The earliest sign of carb icing is usually a slow loss of RPM or manifold pressure, rather than sudden rough running.
❄️ Fuel-injected engines
Fuel-injected engines remove the venturi effect, but icing can still form within the induction system, including intake ducting or the plenum chamber. Reduced airflow and uneven distribution between cylinders lead to subtle, progressive power loss, which can be harder to spot early on.
What do pilots tend to notice first?
• A reduction in RPM or engine power
• Sluggish throttle response
• Slight rough running or a change in engine note
Often this happens before any visible airframe ice is present.
Engine icing is rarely about extreme weather; it’s about time, moisture and airflow. Knowing how and where ice forms inside the engine helps turn small clues into useful information before they become bigger problems.
❄️ Happy safe icy days! ❄️