Fuel Systems and Fuel Management
Tanks and supply
Know the tank types: integral, bladder and rigid. Integral tanks use the wing structure and sealant, so inspection matters. Understand the supply path from tank to engine: boost pump, selector valve, filter, and engine-driven pump. Traps include the question of why a boost pump is used at altitude or during take-off, and the difference between a fuel selector and a shut-off valve.
Quantity and flow indication
Quantity is measured by float, capacitance or resistance senders; flow is measured by a flowmeter. Know that capacitance gauges measure mass-related quantity less directly than a float gauge measures volume, and that fuel quantity and flow are separate indications. Traps include assuming a flow indication proves tank quantity, and forgetting that a fuel pressure gauge may read zero with the engine driven pump only at low power.
Fuel management
Understand tank selection, balancing, unusable fuel, and the reason for sumping drains to remove water and sediment. Know the effect of temperature on fuel density and why refuelling figures use density. Traps include the difference between total fuel and usable fuel, and the requirement to check for water after refuelling.
Worked example
If one tank drains faster than the other, suspect a crossfeed or selector position error rather than a gauge fault. Rule of thumb: always confirm quantity by dipstick or gauge before flight, and treat unusable fuel as absent for planning.