AF Aircraft Fuel Systems

Fuel jettisoning is usually accomplished

through a common manifold and outlet in each wing.
by gravity flow into the outboard wing tanks and overboard through a common outlet in each wing.
through individual outlets for each tank.

The primary purpose of an aircraft’s fuel jettison system is to quickly achieve a

lower landing weight.
balanced fuel load.
reduced fire hazard.

The fuel jettison valve must be designed to allow flight personnel

to close the valve at any time and the fuel must discharge clear of the aircraft.
to discharge fuel clear of the aircraft.
to close the valve at anytime.

Which of the following is employed to maintain lateral stability when jettisoning fuel?

Two separate independent systems.
Crossfeed system.
Two interconnected systems.

A fuel jettison system is required under certain conditions if the maximum takeoff weight exceeds the maximum landing weight. What regulations cover the requirements of fuel jettisoning?

14 CFR Parts 43 and 91.
14 CFR Parts 23 and 25 and CAM 4b.
14 CFR Parts 21 and 43 and CAM 8.

Fuel is moved overboard in most fuel jettison systems by

boost pumps.
gravity.
gravity and engine-driven fuel pumps.

Fuel jettisoning past the limits prescribed by Federal Aviation Regulations is usually prevented by

closely monitoring the fuel quantity and turning off the fuel dump switch(es).
dump limit valves or a low-level circuit.
standpipes in the fuel tanks.

Which procedure must be followed when defueling aircraft with sweptback wings?

Defuel all the tanks at one time.
Defuel the inboard wing tanks first.
Defuel the outboard wing tanks first.

Refer to Figure 17. What is the purpose of the pump crossfeed valve?

Balance the fuel in the tanks.
Allow operation of engines from one tank.
Allow operation of the left engine when the right fuel-boost pump is inoperative.

Normal fuel crossfeed system operation in multi-engine aircraft

calls for jettisoning of fuel overboard to correct lateral instability.
reduces contamination and/or fire hazards during fueling or defueling operations.
provides a means to maintain a balanced fuel load condition.

How may vents, arranged so that they are not likely to become plugged at the same time, must be used in multi-engine fuel systems?

Two.
Four.
Six.

What is the primary purpose of the crossfeed system?

It allows any tank to supply fuel to any engine.
It bypasses the engine shutoff valve if it fails.
It divides the fuel and sends it to the injectors.

Fuel system components must be bonded and grounded in order to

drain off static charges.
prevent stray currents.
retard galvanic corrosion.

How many engine-driven fuel pumps per engine are required for engines requiring fuel pumps?

Two engines can share one fuel pump.
One fuel pump for each engine.
Two fuel pumps for each engine.

A typical large transport aircraft fuel manifold system allows how many of the following?

1. All tanks can be serviced through a single connection.
2. Any engine can be fed from any tank.
3. All engines can be fed from all tanks simultaneously.
4. A damaged tank can be isolated from the rest of the fuel system.

1. and 2.
1, 2, and 3.
1, 2, 3, and 4.

A fuel system must be designed to prevent fuel vapor ignition caused by

overheating.
backfire.
lightning.

What is the minimum distance allowed between a fuel tank and the fire wall separating the engine?

One-half inch.
One inch.
Two inches.

Fuel baffles are installed in tanks to prevent __________________ caused by changes in the attitude of the aircraft.

vapors.
surging.
starvation.

Many fuel tanks incorporate _________________________ valves to prevent fuel from flowing away from the boost pump or tank outlet when the aircraft is in a high-G maneuver.

flapper
check
dump

Fuel heaters are used with fuel systems for turbine engines to prevent _________________ in the fuel from clogging system filters.

moisture.
ice crystals.
contamination.

A transducer in a fuel pressure system serves what function?

Transmits an electrical signal to the transmitter for fluid pressure.
Transmits electrical signal proportional to the fluid pressure.
Converts fluid pressure directly through a transmitter to the indicator.

The use of turbine fuels in aircraft has resulted in some problems not normally associated with aviation gasolines. One of these problems is

increasing viscosity of fuel as fuel temperature lowers at altitude.
higher vapor pressure.
microbial contaminants.

What is used in many aircraft to prevent bubbles in the fuel after it leaves the tank when atmospheric pressure is lower than fuel vapor pressure?

Air-fuel separators.
Anti-foaming additives.
Boost pumps.

Which of the following precautions is most important during refueling operations?

All outside electrical sources must be disconnected from the aircraft.
Fuel to be used must be appropriately identified.
All electrical switches must be in OFF position.

Before fueling an aircraft by using the pressure fueling method, what important precaution should be observed?

The truck pump pressure must be correct for the refueling system.
The truck pump pressure must be adjusted for minimum filter pressure.
The aircraft’s electrical system must be on to indicate quantity gauge readings.

What flight safety-related advantage does a pressure fueling system provide?

Keeps the aircraft within weight and balance limitations.
Reduces the chances for fuel contamination.
Reduces the time required for fueling.

Aircraft pressure fueling systems instructional procedures are normally placarded on the

fuel control panel access door.
lower wing surface adjacent to the access door.
aircraft ground connection point.

Pressure fueling of aircraft is usually accomplished through

pressure connections on individual fuel tanks.
at least one single point connection.
individual fuel tank overwing and/or fuselage access points.

Which of the following may be used for the repair of fuel leaks on most integral fuel tanks?

Welding and resealing.
Brazing and resealing.
Riveting and resealing.

How is the outlet fuel pressure regulated on a submerged, single-speed, centrifugal-type fuel pump?

By the engine-driven pump’s design and internal clearance.
By the first check valve downstream from the pump.
By the pump’s design and internal clearances.

What is one purpose of a fuel tank vent?

To maintain atmospheric pressure.
To decrease fuel vapor pressure.
To decrease tank internal air pressure.

When inspecting a removable rigid fuel tank for leaks, what procedure should be followed?

pressurize the tank with air and brush with soapy water.
fill the tank with water and pressurize with air brush with soapy water.
pressurize the tank with air and submerge in water to locate leaks.

If it is necessary to enter an aircraft’s fuel tank, which procedure should be avoided?

Continue purging the tank during the entire work period.
Station an assistant outside the fuel tank access to perform rescue operations if required.
Conduct the defueling and tank purging operation in an air-conditioned building.

What is the recommended practice for cleaning a fuel tank before welding?

Purge the tank with air.
Flush the inside of the tank with clean water.
Steam clean the tank interior.

An aircraft’s integral fuel tank is

usually located in the bottom of the fuselage.
a part of the aircraft structure.
a self-sealing tank.

Which gas is used for purging an aircraft fuel tank?

Helium or argon.
Carbon dioxide.
Carbon monxide.

Why is the main fuel strainer located at the lowest point in the fuel system?

It traps any small amount of water that may be present in the fuel system.
It is near the fuel tank heater to help prevent vapor lock in the system.
It filers and traps all micro-organisms that may be present in the fuel system.

The purpose of a diaphragm in a vane-type fuel pump is to

equalize fuel pressure at all speeds.
vary fuel pressure according to throttle setting.
compensate fuel pressures to altitude changes.

When moving the mixture control on a normally operating engine into the idle cutoff position, engine RPM should

slightly increase before the engine starts to die.
slightly decrease and then drop rapidly.
remain the same until the cutoff is effected, then drop rapidly.

Entrained water in aviation turbine fuel is a hazard because of its susceptibility to freezing as it passes through the filters. What are common methods of preventing this hazard?

Micromesh fuel strainers and fuel heater.
High-velocity fuel pumps and fuel heater.
Anti-icing fuel additives and fuel heater.

As a general rule, which statement is true regarding fuel leaks?

Stains, seeps, and heavy seeps are not flight hazards.
All fuel leaks regardless of location or severity are considered a hazard to flight.
Stains, seeps, and heavy seeps (in addition to running leaks) are considered flight hazards when located in unvented areas of the aircraft.

The presence of fuel stains around a fuel nozzle would indicate

too much fuel pressure.
excessive airflow across the venturi.
clogged fuel nozzle.

What should be used to inert an integral fuel tank before attempting repairs?

C0₂.
Water.
Steam.

What should be used to remove flux from an aluminum tank after welded repairs?

Soft brush and warm water.
Five percent solution of nitric or sulfuric acid.
Mild solution of soap and warm water.

What method would be used to check for internal leakage of a fuel valve without removing the valve from the aircraft?

Place the valve in the OFF position, drain the strainer bowl, and with boost pump on, watch to see if fuel flows to the strainer bowl.
Remove fuel cap(s), turn boost pump(s) on, and watch for bubbling in the tanks.
Apply regulated air pressure on the downstream side of the fuel pump and listen for air passing through the valve.

Why are jet fuels more susceptible to water contamination than aviation gasoline?

Jet fuel has a higher viscosity than gasoline.
Jet fuel is lighter than gasoline, therefore, water is more easily suspended.
Condensation is greater because of the higher volatility of jet fuels.

When installing a rigid fuel line, 1/2 inch in diameter, at what intervals should the line be supported?

24 inches.
12 inches.
16 inches.

The probe of a capacitance-type fuel level gauge is essentially a

float-actuated variable capacitor.
capacitor with fuel and air acting as one plate.
capacitor with fuel and air acting as a dielectric.

Which statement concerning an electronic capacitance-type fuel quantity indicating system is true?

it has no moving parts in the tank.
it has two tubes separated by an electronic field in the tank.
It utilizes a variable capacitor to indicate the fuel tank capacity.

What type of remote-reading fuel quantity indicating system has several probes installed in each fuel tank?

Electromechanical.
Electronic.
Direct reading.

Which aircraft fuel quantity indicating system incorporates a signal amplifier?

Electronic.
Sight glass.
Electrical.

A drip gauge may be used to measure

the amount of fuel in the tank.
system leakage with the system shut down.
fuel pump diaphragm leakage.

The electronic-type fuel quantity-indicating system consists of a bridge circuit.

an amplifier, an indicator, and a tank unit.
a tank, an amplifier, and an indicator.
a tank unit, a tank, and an amplifier.

A probe or a series of probes is used in what kind of fuel quantity indicating system?

Selsyn.
Capacitor.
Synchro.

Why is the capacitance fluid quantity indicating system more accurate in measuring fuel level than a mechanical type?

Only one probe and one indicator are necessary for multiple tank configurations.
It measures in gallons and converts to pounds.
It measures by weight instead of volume.

One advantage of electrical and electronic fuel quantity indicating systems is that

the indicators are calibrated in gallons; therefore, no conversion is necessary.
only one transmitter and one indicator are needed regardless of the number of tanks.
several fuel tank levels can be read on one indicator.

A fuel totalizer is a component which indicates the

total amount of fuel being consumed by all engines.
amount of fuel in any given tank.
amount of fuel in all tanks.

A digital fuel totalizer automatically indicates the amount of fuel used, fuel remaining, current rate of consumption, and fuel

weight aboard at takeoff.
remaining at the 45-minute IFR fuel reserve.
remaining, flight time at the current power setting.

What is the dielectric (nonconducting material) in a capacitance-type fuel quantity indicating system?

Outer shell of the capacitor.
Fuel in the tank.
Fuel and air in
the tank.

A capacitance-type fuel quantity indicating system measures fuel in

pounds.
pounds per hour.
gallons.

What are the four general types of fuel quantity gauges?

Sight glass, mechanical, electrical, and electronic.
Electrical, electronic, bourbon tube, and litmus indicator.
Electrical, direct reading static pressure type, sight glass, and litmus indicator,

How does temperature affect fuel weight?

Cold fuel is heavier per gallon.
Warm fuel is heavier per gallon.
Temperature has no effect.

One advantage of electrical and electronic fuel quantity indicating systems is that the indicator

can be located any distance from the tank(s).
has no movable devices.
always measures volume instead of mass.

When fuel quantity is measured in pounds instead of gallons, the measurement will be more accurate because fuel volume

varies with temperature change.
increases when temperature decreases.
varies with changes in atmospheric pressure.

An electrical type fuel quantity indicating system consists of an indicator in the cockpit and a float

in the tank that moves a connecting arm to the wiper on a variable resistor in the tank.
attached to a rod that moves up or down in a calibrated cylinder.
in the tank that operates with alternating current and uses constant resistance in a circuit to drive a ratiometer-type indicator.

What is the purpose of a float-operated transmitter installed in a fuel tank?

It sends an electric signal to the fuel quantity indicator.
It senses the total amount of fuel density.
It senses the dielectric qualities of fuel and air in the tank.

In an electronic-type fuel quantity indicating system, the tank sensing unit is a

capacitor.
variable resistor.
variable inductor.

What must each fuel quantity indicator be calibrated to read during level flight when the quantity of fuel remaining is equal to the unusable fuel supply?

The total unusable fuel quantity.
Both the total unusable fuel quantity and the unusable fuel quantity in each tank.
Zero.

What unit would be adjusted to change the fuel pressure warning limits?

Fuel flowmeter bypass valve.
Pressure-sensitive mechanism.
Fuel pressure relief valve.

Select one means of controlling the fuel temperature on turbine-powered aircraft.

Engine bleed air to the fuel filter.
Engine bleed air to the fuel tank.
Engine bleed air to a heat exchanger.

What is the purpose of flapper-type check valves in integral fuel tanks?

To allow defueling of the tanks by suction.
To prevent fuel from flowing away from the boost pumps.
To allow the engine-driven pumps to draw fuel directly from the tank if the boost pump fails.

What unit is generally used to actuate the fuel pressure warning system?

Fuel flowmeter.
Pressure-sensitive mechanism.
Fuel pressure gauge.

What method is used on turbine-powered aircraft to determine when the condition of the fuel is approaching the danger of forming ice crystals?

Fuel pressure warning.
Fuel pressure gauge.
Fuel temperature indicator.

Which of the following would give the first positive indication that a change-over from one fuel tank to another is needed?

Fuel pressure warning.
Fuel pressure gauge.
Fuel quantity indicator.

A fuel pressure warning switch contacts close and warning light is turned on when

a measured quantity of fuel has passed through it.
the fuel flow stops.
the fuel pressure drops below specified limits.

A transmitter in a fuel pressure warning system serves what function?

Transmits an electrical signal to fluid pressure.
Converts fluid pressure to an electrical signal.
Transmits fluid pressure directly to the indicator.

Where is fuel pressure taken for the pressure warning signal on most aircraft engines?

Outlet side of the boost pump.
Fuel pressure line of the carburetor.
Between the fuel pump and the strainer.

Which of the following is necessary to effectively troubleshoot a fuel pressure warning system?

The manufacturer’s maintenance manuals.
AC 43.13-1B, Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair.
A set of Federal Aviation Requirements.

Which of the following would be most useful to locate and troubleshoot an internal fuel leak in an aircraft fuel system?

Structural repair manual.
Orthographic projection troubleshooting tree.
Maintenance manual diagrams and descriptions.

In some aircraft with several fuel tanks, the possible danger of allowing the fuel supply in one tank to become exhausted before the selector valve is switched to another tank is prevented by the installation of

a fuel pressure warning signal system.
a fuel pressure relief valve.
an engine fuel pump bypass valve.

The function of a fuel heater is to

protect the engine fuel system from ice formation.
protect the fuel from freezing.
heat the fuel to combustion temperature.

(1) Gas-turbine engine fuel systems are very susceptible to the formation of ice in the fuel filters.

(2) A fuel heat operates as a heat exchanger to warm the fuel.

Regarding the above statements,

only 1 is true.
only 2 is true.
both 1 and No. 2 are true.

(1) A fuel heater can use engine bleed air as a source of heat.

(2) A fuel heater can use engine lubricating oil a a source of heat.

Regarding the above statements,

only 1 is true.
both 1 and 2 are true.
neither 1 nor 2 is true.

(1) A fuel pressure gauge is a differential pressure indicator.

(2) A fuel pressure gauge indicates the pressure of the fuel entering the carburetor.

Regarding the above statements,

only 2 is true.
both 1 and 2 are true..
neither 1 nor 2 is true.

A fuel pressure relief valve is required on an aircraft

positive-displacement fuel pump.
centrifugal boost fuel pump.
positive-displacement fuel pump and centrifugal boost fuel pump.

The primary purpose of a fuel tank sump is to provide a

way to shut off fuel flow or to route the fuel to a desired location.
place for contaminants and water to settle, with a drain valve to remove the impurities.
way to manually operate valves on a fuel tank to isolate or direct fuel to a pump..

Why are integral fuel tanks used in many large aircraft?

To reduce fire hazards.
To facilitate servicing.
To reduce weight.

When an aircraft is fueled from a truck or fuel farm that has not been contaminated, daily draining

is not required because fuel trucks and fuel farms may make use of laser contaminant identification technology.
of strainers and sumps is combined with periodic filter changes and inspection to ensure fuel is contaminant free.
is only required if the fuel truck or farm has not been in continuous service.

When defueling an aircraft, which of the following must be accomplished?

Defuel inside the hangar when fire suppression is available.
Defuel outside the hangar when possible.
Always defuel outside the hangar.

Integral fuel tanks on transport aircraft are

easily removed for service or inspection.
constructed of plastic or fiberglass.
supported by the aircraft structure.

What precautions must be observed if a gravity-feed fuel system is permitted to supply fuel to an engine from more than one tank at a time?

The tank airspaces must be interconnected.
The fuel outlet ports of each tank must have the same cross-sectional area.
Each tank must have a valve in its outlet that automatically shuts off the line when the tank is empty.

The purpose of the baffle plate in a fuel tank is to

provide an expansion space for the fuel.
resist fuel surging within the fuel tank.
provide internal structural integrity.

What markings must be placed on or near each appropriate fuel filler cover on standard category aircraft?

The word “Avgas” and the minimum fuel grade, and the total fuel tank capacity.
The word “Avgas” and the minimum fuel grade or designation for the engines, and the usable fuel tank capacity.
The word “Avgas” and the minimum fuel grade.

What is one disadvantage of using aromatic aviation fuels?

A fuel intercooler is required.
Deteriorates rubber parts.
Results in low fuel volatility.

Fuel-boost pumps are operated

to provide a positive flow of fuel to the engine.
primarily for fuel transfer.
automatically from fuel pressure.

Flapper valves are used in fuel tanks to

reduce pressure.
prevent a negative pressure.
act as check valves.

Why are centrifugal-type boost pumps used in fuel systems of aircraft operating at high altitude?

Because they are positive displacement pumps.
To supply fuel under pressure to engine-driven pumps.
To permit cooling air to circulate around the motor.

Why is it necessary to vent all aircraft fuel tanks?

To ensure a positive head pressure for a submerged boost pump.
To exhaust fuel vapors.
To limit pressure differential between the tank and atmosphere.

According to Part 23, what minimum required markings must be placed at or near each appropriate fuel filler cover for reciprocating engine-powered airplanes?

The word “Avgas” and the minimum fuel grade.
The word “Fuel” and usable fuel capacity.
The word “Avgas” and the total fuel capacity.

The location of leaks and defects within the internal portions of the fuel system can usually be determined by

visual inspection for evidence of wet spots and stains, and feeling for unusually warm components.
performing a fuel flow check.
observing the pressure gauge and operating the selector valves.

What type of fuel-booster pump requires a pressure relief valve?

Concentric.
Sliding vane.
Centrifugal.

To prevent vapor lock in fuel lines at high altitude, some aircraft are equipped with

vapor seaprators.
direct-injection-type carburetors.
booster pumps.

Some turbine-powered aircraft have a fuel temperature indicator located in the cockpit to

monitor the fuel flow in the event that ice crystals form in the fuel system.
monitor the fuel temperature during high altitude flight.
ascertain the amount of fuel onboard the aircraft when ice starts to form in the fuel tanks.

When inspecting a fuel system, you should check all valves located downstream of boost pumps with the pumps.

at idle.
dormant.
operating.

The type of fuel-boost pump that separates air and vapor from the fuel before it enters the line to the carburetor is the

gear-type pump.
centrifugal-type pump.
sliding vane-type pump.

On a large aircraft pressure refueling system, a pressure refueling receptacle and control panel will permit one person to

fuel or defuel any of the tanks on an aircraft.
fuel any of the tanks on an aircraft.
defuel any of the tanks on an aircraft.

When routing a fuel line between two rigidly mounted fittings the line should

have at least one bend between such fittings.
be a straight length of tubing and clamped to the aircraft structure.
have a flexible line added between two metal lines to allow for ease of installation.

Which of the following tests can determine an aviation gasoline’s tendency to vapor lock?

Reid vapor pressure test.
Octane vapor pressure test.
True vapor pressure test.

Microbial growth is produced by various forms of micro-organisms that live and multiply in the water interfaces of jet fuels. Which of the following could result if microbial growth exists in a jet fuel tank and is not corrected?

interference with fuel flow, interference with fuel quantity indicators, and electrolytic corrosive action in a metal tank.
Interference with fuel quantity indicators, engine seizure, or a lower grade rating of the fuel.
Interference with fuel flow, lower grade rating of the fuel, and electrolytic corrosive action in a rubber tank.

The vapor pressure of aviation gasoline is

lower than the vapor pressure of automotive gasoline.
higher than the vapor pressure of automotive gasoline.
approximately 20 psi at 100 degrees F.

What can be done to eliminate or minimize the microbial growth problem in an aircraft jet fuel tank?

Use anti-icing and antibacterial additives.
Add CO₂ as a purgative.
Keep the fuel tank topped off.

What is the maximum vapor pressure allowable for an aircraft fuel?

7 psi.
5 psi.
3 psi.

If a bladder-type fuel tank is to be left empty for an extended period of time, the inside of the tank should be coated with a film of

engine oil.
linseed oil.
ethylene glycol.

How may the antiknock characteristics of a fuel be improved?

By adding a knock inhibitor.
By adding a knock enhancer.
By adding a fungicide agent.

AF Aircraft Fuel Systems

Jon K

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