Aircraft Systems Exam 4/ Weaver/ Kent

Which aircraft typically use gravity-fed fuel systems?

High-wing aircraft; gravity moves fuel to the engine.

Do bladder tanks require large access openings?

No. They can be folded or rolled through smaller openings.

What are the three basic fuel tank types?

Rigid removable, bladder, and integral (wet wing).

Required gravity-fed fuel flow vs. takeoff consumption?

150% of the engine's takeoff fuel consumption.

What is the primary purpose of an aircraft fuel system?

Provide uninterrupted usable fuel at the required flow and pressure.

What type of pump is an engine primer?

Single-action piston pump.

How many tanks may a fuel pump draw from directly at once?

One tank at a time.

What type of filter is a fuel tank finger screen?

Coarse wire-mesh strainer.

What is vapor lock?

Fuel vapor bubbles restrict or interrupt liquid fuel flow.

What fuel indicator is required on all aircraft?

Fuel quantity indicator.

What is a gascolator?

A fuel strainer with a sediment collection bowl.

Which filter handles high pressure after the engine-driven pump?

Micronic wafer filter, before the fuel metering device.

Are helicopter and fixed-wing fuel systems completely different?

No. They share many components and technologies.

What must withstand vibration, inertia, and fluid loads?

The fuel tank, including structural loads.

Can welding be an approved rigid fuel tank repair?

Yes, when approved by the manufacturer and performed safely.

Required pump-fed flow for reciprocating engines?

125% of fuel needed at maximum takeoff power.

Required fuel flow for turbine engines?

At least 100% under intended conditions and maneuvers.

What is fuel system independence?

One component failure must not cause power loss in more than one engine.

What is unusable fuel?

Fuel that cannot reliably be delivered under adverse fuel-feed conditions.

Minimum fuel tank expansion space?

2% of tank capacity.

What do tank vents do?

Maintain pressure as fuel leaves the tank.

Why are tank sumps installed?

Collect water and sediment for draining.

Why do pump-fed aircraft select one tank at a time?

An empty tank could introduce air into the pump.

Which aircraft commonly use pump-feed systems?

Low-wing and mid-wing aircraft.

What is the simplest fuel system?

Gravity-feed; no fuel pump required.

Why do multiengine aircraft have crossfeed?

To allow an engine to draw fuel from another main tank.

What is the main advantage of rigid removable tanks?

They can be removed and repaired.

What materials are rigid tanks commonly made from?

Aluminum alloy or stainless steel.

What are bladder tanks made from?

Reinforced flexible material.

Why must bladder tank bottoms be smooth?

Wrinkles can trap water and cause fuel starvation.

Why must bladder tanks remain wet during storage?

To prevent rubberized material from cracking.

What is an integral fuel tank?

A sealed section of wing or fuselage structure.

Main advantage of integral fuel tanks?

Maximum fuel volume with minimum weight.

What do fuel tank baffles prevent?

Excessive fuel sloshing.

Why are flexible fuel lines used?

To accommodate vibration between components.

Where are stainless steel fuel lines often used?

Damage-prone areas such as wheel wells and engine compartments.

What do fuel valves control?

Fuel shutoff and routing between system components.

Name three hand-operated fuel valve types.

Cone, poppet, and gate.

How do cone valves control fuel flow?

Rotating passageways align with selected fuel ports.

How do poppet valves control fuel flow?

A cam opens the selected port while others close.

How does a gate valve stop fuel?

A sealed blade moves into the fuel flow path.

Why use motor-operated fuel valves?

Remote operation, especially on large aircraft.

What is a key feature of solenoid fuel valves?

They open and close very quickly.

What is the primary engine fuel delivery pump?

Engine-driven fuel pump.

What are auxiliary boost pumps used for?

Backup, engine starting, and high-altitude operation.

What is the most common auxiliary fuel pump?

Centrifugal boost pump.

Where are centrifugal boost pumps located?

Inside the fuel tank or beneath it.

How does a centrifugal pump move fuel?

An impeller draws fuel centrally and expels it outward.

What principle do ejector pumps use?

Bernoulli's principle through a venturi.

Why are ejector pumps used?

Maintain fuel supply to in-tank pumps and prevent cavitation.

How does a pulsating electric pump operate?

A solenoid moves a plunger back and forth.

What is a wobble pump?

A hand-operated backup fuel pump.

What is the main purpose of fuel filters?

Remove contaminants before fuel reaches the engine.

What do micronic filters remove?

Very small particles; turbine filters commonly target 10–25 microns.

Why do some micronic filters have bypass valves?

To maintain fuel flow if the filter becomes blocked.

Why are turbine aircraft fuel heaters used?

To prevent or melt ice that could block filters.

What are common fuel-heating methods?

Compressor bleed air or oil/fuel heat exchangers.

How do float-type fuel gauges work?

A float follows fuel level and drives an indicator.

How do capacitance fuel gauges measure quantity?

Fuel level changes the capacitance between probe plates.

What are the four fuel leak classifications?

Stain, seep, heavy seep, and running leak.

Which regulations govern aircraft fuel system design?

14 CFR Parts 23, 25, 27, 29, and 31.

What is the purpose of fuel system lightning protection?

Prevent ignition of fuel vapor from lightning-related discharges.

What is corona discharge?

Electrical discharge between the aircraft and surrounding atmosphere.

Can a fuel tank be installed on the engine side of a firewall?

No; at least ½ inch clearance from the firewall is required.

How must fuel tanks be isolated from personnel compartments?

By a fume-proof, fuel-proof enclosure vented and drained outside.

Required sump capacity for reciprocating engine systems?

1 fluid ounce per 20 gallons of fuel.

Maximum gasoline aircraft fuel filler opening?

2.35 inches.

Minimum turbine-fuel aircraft filler opening?

2.95 inches.

equired pressure-fueling system strength?

2 times the maximum likely surge pressure.

What must fuel tank vents prevent?

Excessive pressure differences and fuel loss

What are the two main aviation fuel categories?

Aviation gasoline (AVGAS) and turbine (jet) fuel.

Which jet fuel is most common in the United States?

Jet A.

Which jet fuel is more common internationally?

Jet A-1.

How does Jet B differ from Jet A?

Jet B is more volatile; it is a wide-cut fuel.

What is JP-8?

Military jet fuel similar to Jet A-1 with added inhibitors

What is fuel volatility?

How readily fuel vaporizes

Why is jet fuel icing a concern?

Water can freeze and obstruct filters or fuel flow.

What do fuel-consuming microbes require?

Fuel and water

What damage can microbial contamination cause?

Clogged filters, corroded coatings, and degraded fuel.

How can microbial growth be controlled?

Reduce water accumulation; biocides may be used.

What is the purpose of AN/MS fuel fittings?

Connect rigid aircraft fuel lines.

Why electrically bond metal fuel system components?

Reduce static electricity and ignition risk.

What is the purpose of a fuel line fire sleeve?

Protect flexible fuel lines from fire and heat.

How does a ratiometer fuel gauge work?

Float resistance changes coil current and pointer position.

What do digital fuel indicators convert?

Variable resistance into a digital display signal.

Why are capacitance gauges common on large aircraft?

More accurate; no moving tank-sender parts.

What is the purpose of a fuel gauge compensator?

Correct for fuel temperature and dielectric changes.

What are the five main fuel contaminants?

Water, particles, surfactants, microbes, and foreign fuel

What do surfactants do to fuel contamination?

Keep water and particles suspended; reduce filter effectiveness

How can fuel contamination be checked?

Sump sampling, visual inspection, and test kits

What are the two main aircraft refueling methods?

Over-the-wing and pressure refueling

Where should aircraft normally be refueled?

Outside, not inside a hangar.

Why bond aircraft before fueling or defueling?

Prevent static discharge and possible ignition.

Why might an aircraft be defueled?

Maintenance, inspection, or contamination.

How are pressure-fueled aircraft commonly defueled?

Through the pressure-fueling port.

How are bladder fuel tank leaks repaired?

Manufacturer-approved patches and adhesive

How are integral fuel tank leaks repaired?

Replace damaged sealant or access-panel seals.

What safety step is essential before welding a fuel tank?

Remove fuel vapors to prevent explosion

What is a fuel tank sloshing repair?

Coating the tank interior with approved fuel-resistant sealant.

What is required before entering a large fuel tank?

Ventilate and test for dangerous vapors; follow entry procedures.