Aircraft Fuel Systems practice questions

Answer: B) Vapor lock

• AIncorrect. Icing happens in cold conditions.
• BCorrect. Vapor bubbles can interrupt fuel flow to the engine.
• CIncorrect. This is not caused by heat.
• DIncorrect. This is not the term.

Answer: B) Remove the old sealant and clean the area with an approved solvent

Before resealing, the tank is defueled and purged. The old sealant is then removed and the area cleaned with an approved solvent so the new sealant bonds to clean, dry metal.

• AIncorrect. New sealant will not bond reliably to old, damaged or fuel-soaked sealant, and the leak path stays open.
• BCorrect. The damaged sealant must be removed and the surface cleaned of fuel and contaminants so the new sealant can bond.
• CIncorrect. Steel particles left on aluminum structure cause dissimilar-metal corrosion. Old sealant is removed with nonmetallic tools.
• DIncorrect. Oil or grease on the surface keeps the sealant from bonding. The surface must be clean and dry.

Answer: A) Moving fuel from one tank to another to keep lateral balance and the CG within limits

On large aircraft, the fuel transfer system moves fuel between tanks to manage balance and CG. Jettison, crossfeed, and pressure refueling are separate functions.

• ACorrect. A transfer system pumps fuel between tanks, for example from a center or auxiliary tank to a wing tank. This manages weight distribution, keeps lateral balance, and holds the CG within limits.
• BIncorrect. Dumping fuel overboard is the job of the fuel jettison system (14 CFR 25.1001), not the transfer system. Transferred fuel stays on board.
• CIncorrect. That is the crossfeed system, which supplies engines from tanks that normally do not feed them. Transfer moves fuel from tank to tank, not from a tank to an engine.
• DIncorrect. That describes the single-point (pressure) refueling manifold used on the ground. It is not the system used to shift fuel between tanks for balance.

Answer: A) Microbial growth living at the fuel-water interface

Black, slimy sludge at the fuel-water interface is the typical sign of microbial growth. Removing water by draining sumps regularly, and using biocides or FSII, helps prevent it.

• ACorrect. Bacteria and fungi live in free water and feed on the hydrocarbons at the fuel-water interface. They form dark, slimy mats and sludge that can clog filters, corrode tanks and upset fuel-quantity probes.
• BIncorrect. Surfactants (soap-like compounds) usually show up as a brownish, soapy liquid or emulsion that keeps water suspended in the fuel. They do not form a black, living slime.
• CIncorrect. Overheating fuel leaves hard carbon (coke) varnish on hot surfaces such as nozzles and heat exchangers. It does not create slime at the water layer in a tank sump.
• DIncorrect. FSII is mixed into jet fuel partly to inhibit microbial growth. It is not the source of black, slimy sludge.

Answer: A) A separate tank, often aluminum, that can be removed

• ACorrect. It is not part of the wing structure.
• BIncorrect. That is an integral tank.
• CIncorrect. That is a bladder tank.
• DIncorrect. Fuel tanks hold fuel.

Answer: D) By gravity from the wing tanks

• AIncorrect. Gravity feed is normal.
• BIncorrect. Bleed air is not used in light aircraft.
• CIncorrect. Vacuum pumps drive instruments.
• DCorrect. Fuel flows down to the engine without a boost pump.

Answer: A) Bond the aircraft to the defueling truck or equipment with a bonding cable

Before fueling or defueling, the aircraft is bonded to the fuel truck or equipment so both are at the same electrical potential. This prevents a static spark from igniting fuel vapors.

• ACorrect. Bonding the aircraft to the fuel truck or equipment puts both at the same electrical potential. This keeps static from discharging as a spark where fuel vapors are present.
• BIncorrect. Grounding the truck alone does not equalize the charge between the truck and the aircraft. FAA guidance stresses bonding the aircraft to the fuel source.
• CIncorrect. Sump draining is a fuel contamination check. It does nothing to control static charge during fuel transfer.
• DIncorrect. Opening access panels is not part of a defueling setup. It would release more vapor into the work area and raise the fire hazard.

Answer: A) An outboard tank in the vent system that catches fuel entering the vent lines and returns it to the tanks

A surge tank is a vent-system compartment, usually near the wingtip, that catches fuel entering the vent lines. It returns that fuel to the tanks so it is not spilled overboard.

• ACorrect. The surge tank, usually near the wingtip, is the end point of the vent channels. It catches fuel that enters the vent system during maneuvering, thermal expansion, or refueling, so the fuel is not spilled overboard. The fuel goes back to the main tanks through drain or check (float) valves or a scavenge/jet pump, depending on the design.
• BIncorrect. This is a collector (feed) tank. It feeds the engines and keeps the boost pumps covered. It is not part of the vent system.
• CIncorrect. That is the tank's expansion space, an empty volume inside the fuel tank itself. A surge tank is a separate compartment, connected by the vent channels.
• DIncorrect. That is the tank sump, which is drained to remove water and contaminants. It does not catch fuel from the vent system.

Answer: B) The rate at which fuel is delivered to the engine, in gph or pph

A fuel flowmeter shows the rate of fuel flow to the engine, usually in gallons or pounds per hour. On many fuel-injected piston engines this indicator is actually a pressure gauge marked in flow units.

• AIncorrect. Fuel remaining is shown by the fuel quantity indicating system, not the flowmeter.
• BCorrect. A flowmeter shows the fuel consumption rate. On many fuel-injected piston engines it is a pressure gauge marked in flow units, so a clogged injector nozzle can make it show more flow than is actually reaching the engine.
• CIncorrect. Filter or strainer bypass and differential-pressure indicators are separate from the flowmeter.
• DIncorrect. Pump output is shown on a fuel pressure gauge. A pressure-type 'flowmeter' senses pressure at the injection system but is marked and read as flow.

Answer: B) Choose the supply tank

• AIncorrect. Sampling does that.
• BCorrect. The selector chooses which tank feeds the engine, or shuts fuel off.
• CIncorrect. Heaters do that.
• DIncorrect. Jettison systems do that.