Aircraft Fuel Systems — Page 327, Lesson 413

I want to walk you through the fuel system display first, because that's what you'll actually see in the cockpit on an Airbus. This is Figure 16.7, the electronic fuel system display. It's a single screen that gives you the complete state of the fuel system at a glance, and I'll go through each numbered item so you know exactly what you're looking at. Starting at the top left, item 1 is "Fuel used, each engine." That's the total fuel consumed by each engine since it was started, shown in kilograms. Next to it, item 2 is "Total fuel on Board," which is the total fuel remaining in the aircraft, also in kilograms. So you have the fuel burned and the fuel remaining, both right there. Now the valves. Item 3 is the "Engine fuel shut-off valve." This is the valve that isolates fuel from the engine. Item 4 is the "APU fuel shut-off valve," which does the same job for the Auxiliary Power Unit. Item 5 is the "Cross-feed valve." That's the valve that allows fuel to be transferred between the left and right sides of the fuel system, so one engine can draw from the other side's tank if needed. Then we get to the pumps. Item 6 is the "Wing tank booster pump indication," and in this display it's shown switched off. Item 7 is the "Centre tank booster pump." These booster pumps pressurize the fuel so it can be delivered to the engines. Item 8 is the "Transfer valve indication," which shows the status of the valve used to move fuel between tanks. Now the fuel quantities. Item 9 is "Fuel quantity, right wing outboard." Item 10 is "Fuel quantity, right wing inboard." Item 11 is "Fuel quantity, centre tank." So you can see the fuel in each individual tank section. And item 12 is "Tank fuel temperature," shown in degrees Celsius. You can see the values on the display: 3100 kilograms for the wing tanks, 5030 for the centre tank, and the total on board is 14350 kilograms. The temperatures show -11 degrees Celsius on the left and 7 degrees on the right. Now let's move to the ground side of things, because fuelling an aircraft is a carefully controlled operation. Before any fuelling begins, we establish fuelling zones. These zones extend at least 6 meters, or 20 feet, radially from the filling and venting points on the aircraft and the fuelling equipment. That's the safety perimeter. Within these zones, there are strict restrictions. No smoking, obviously. If an APU is required during fuelling and its exhaust discharges into the zone, then the APU must be started before the filler caps are removed or fuelling connections are made. That's a specific sequence. And if the APU stops for any reason during fuelling, it must not be started again until fuelling has ceased and there's no danger of igniting the fuel vapours. So the rule is: once fuelling starts, a stopped APU stays stopped until the danger is gone. Ground power units, or GPUs, should be located as far away as practical from the fuelling zones, and they must not be connected or disconnected while fuelling is in progress. Fire extinguishers should be located so they're readily accessible. Now, the method of fuelling depends on the aircraft. Light aircraft are refuelled by the overwing method, where fuel is poured into the wing tanks from above, and the quantity issued is shown in litres or gallons on the delivery vehicle. Large aircraft are pressure refuelled. That means fuel is pumped under pressure from hydrants or bowsers through underwing refuel and defuel coupling points. This is controlled by quantity, tank, and valve selection from a conveniently situated refuelling control panel. You can preselect the quantity required in each tank, and the refuel valve to that tank will close automatically when that level is reached. The system will prevent any tank being overfilled. Before fuelling commences, there's a critical precaution: the aircraft should be bonded, or grounded, to the fuelling equipment using dedicated wires and clips. And here's the key point — reliance must not be placed upon anything else for that bonding. That's the electrical connection that prevents a static spark from igniting fuel vapours. So to summarize what we've covered: the cockpit display shows you fuel used per engine, total fuel on board, the shut-off valves for the engines and APU, the cross-feed valve, the booster pumps, the transfer valve, individual tank quantities, and tank temperature. On the ground, fuelling zones are established with a 6-meter radius, strict restrictions apply within them, light aircraft are overwing refuelled, large aircraft are pressure refuelled with preselected quantities, and the aircraft must be bonded to the fuelling equipment with dedicated wires and clips.