We begin with the fuels themselves — Page 310, Lesson 387

This is the start of Chapter 16, Aircraft Fuel Systems. I want to walk you through the full scope of what this chapter covers, because it's a big one and it sets the foundation for everything you'll do with fuel on the line. We begin with the fuels themselves. For piston engines, we're talking about Avgas — aviation gasoline. For gas turbine engines, we use kerosene-based jet fuel. The chapter walks you through the properties of each, and one of the first things you'll notice is fuel colour. Different fuels are dyed different colours so you can tell them apart at a glance — that's a critical safety check before you ever put fuel in an aircraft. Then we get into the problems that can plague fuel. Cloudy fuel — that's a sign of contamination, usually water or ice crystals suspended in the fuel. We look at jet fuel additives, which are chemicals added to combat specific problems. Water in the fuel is a major hazard — it can freeze and block fuel lines, or cause engine failure. Waxing is another issue, where the fuel thickens or forms wax crystals at low temperatures. And boiling — that's a real concern at high altitude, where the reduced atmospheric pressure can cause the fuel to boil even at normal temperatures. We also cover the effects of specific gravity, or SG. That's the density of the fuel compared to water. It matters because it affects how much fuel you can carry by weight, and how the fuel behaves in the tanks. Then we move into the fuel systems themselves. We start with simple, light aircraft fuel systems — the kind you'd find on a single-engine trainer. These can be gravity feed systems, where fuel flows downhill from the tank to the engine, or pressure fed systems, where a pump pushes the fuel. Then we scale up to twin-engine aircraft fuel systems, and finally multi-engine systems, which are far more complex with cross-feed and transfer capabilities. After that, we get into fuel quantity measurement. We look at how the system measures how much fuel is in the tanks, the system function, and the simple quantity measuring systems. Then fuel system instrumentation — the gauges and displays you see in the cockpit. Finally, we cover aircraft refuelling in detail. The precautions before fuelling, during fuelling, and after fuelling. We look at the rules for working on the aircraft during refuelling, and the specific regulations for refuelling with passengers on board — that's EU-OPS 1.305. There are additional instructions for wide-bodied aircraft with automatic inflatable chutes, and separate instructions for aircraft without them. And we finish with special hazards — the things that can go catastrophically wrong if you don't follow the procedures. Let me show you what a simple gravity feed system looks like, because that's where we start. This is Figure 16.1, a single-engine light aircraft gravity feed fuel system. The tank sits above the engine, and fuel flows down by gravity. Simple, but it has limitations — that's why we also have pressure fed systems, which I'll show you next. That's Figure 16.2, the pressure fed system for a single-engine light aircraft, where a pump ensures fuel delivery regardless of tank position. And later, when we get to instrumentation, I'll show you the electronic fuel system display from an Airbus. That's Figure 16.7, and it's a good example of how modern aircraft present fuel information to the pilots. So that's the roadmap for this chapter. We're going to work through it in order — fuels first, then the systems, then measurement, then refuelling procedures. Let's start with the fuels and their properties.