We're starting a brand-new chapter now: Piston Engines – Icing — Page 120, Lesson 149

We're starting a brand-new chapter now: Piston Engines – Icing. This is a critical one, because it deals with a condition that can stop your engine dead, and the book opens with a stark warning. Let me walk you through it. The chapter begins by telling us that the problems of engine icing, particularly in engines fitted with carburettors, have been known for years. Yet, despite modern fuel metering devices, accidents still occur where induction system icing was the cause. So right away, understand that this is not an obsolete problem—it's a live threat even with advanced equipment. Now, the key atmospheric conditions that cause this. Icing in the induction system of all types of piston engine can occur when you have high humidity—specifically, more than 50% Relative Humidity, which we abbreviate as RH—and temperatures ranging from -7°C, which is 20°F, all the way up to as high as +33°C, which is 90°F. That's a surprisingly wide range, and it's important you don't think of icing as only a freezing-cold phenomenon. It can happen in warm air too. Let me show you the chart that illustrates this. This figure shows the range of temperatures at which icing can affect the engine at different power settings. Look at the axes: the horizontal axis is temperature in degrees Celsius, from -20 up to +40. The vertical axis is the dew point in degrees Celsius, from -20 up to +30. And there's a line marked "World wide approximate upper limits of dew point." Now, the chart is divided into zones of icing severity. There's "Light icing" which occurs at cruise or descent power. There's "Moderate icing" at cruise power. There's "Serious icing" at descent power. And there's the worst one, "Serious icing" at any power. So the severity isn't just about how cold it is—it's a combination of temperature, dew point, and what power setting you're using. The message here is that you need to be aware of where you are on this chart relative to your flight phase. The book then makes a very practical point. This temperature range and humidity occur throughout the year in the areas of the United Kingdom and Europe. So this isn't a rare, exotic condition—it's something you'll encounter regularly in that part of the world. Therefore, pilots should be constantly aware of the possibilities of icing and take the corrective action necessary before such problems arise and the situation becomes irretrievable. And here's the sobering conclusion: once an engine stops due to induction icing, it is most unlikely that it may be restarted in time to prevent an accident. That's why recognition and correction are vital. You don't get a second chance to fix this after the engine quits—you have to catch it and act while it's still running. So the core takeaway from this opening section: induction icing is a real, known, and still-occurring hazard, driven by high humidity above 50% RH and temperatures from -7°C to +33°C. The severity depends on your power setting, and the conditions are common in the UK and Europe year-round. And because a stalled engine likely won't restart in time, your job is to recognize the signs and correct the situation before it becomes fatal.