Fuel Distribution - Fuel Systems - Airframes & Aircraft Systems #66

Summary

This lesson delves into aircraft fuel systems, highlighting their critical role in storing and delivering fuel to engines. It discusses the systems' ability to prevent engine starvation, especially during high-demand phases like takeoff. The video covers various components, including tanks, pumps, filters, and valves, and their functions in both single and multi-engine aircraft. It also touches on advanced features like vent systems, cross-feed capabilities, and fuel dump systems, essential for maintaining aircraft performance and safety.

Takeaways

• 🛩 The aircraft fuel system's primary function is to store and deliver fuel to the engine, ensuring it never runs out, even during critical flight phases.
• ✈️ Large aircraft like the Boeing 747 can consume up to 10,000 kg of fuel per engine per hour during takeoff.
• 💧 Fuel tanks in light aircraft are typically rigid and located in the wings, filled through a filler cap and refueling pipe.
• 🔧 Mechanical or electrical pumps draw fuel from the tanks, while a hand-operated selector allows the pilot to choose the fuel source or cut off the supply.
• 🚫 A strainer in the system filters out debris before fuel reaches the engine to prevent damage.
• 🔋 Piston engines may require priming with fuel before starting, which is done through a hand-operated priming pump.
• 📊 Multi-engine aircraft have more complex fuel systems with features like integral wing tanks, center tanks, and sometimes tanks in the fin or stabilizer.
• 💨 A vent system in fuel tanks equalizes air pressure above the fuel with ambient pressure, preventing issues during altitude changes.
• 🔁 Boost pumps in each tank are crucial for high-altitude operations, preventing cavitation and low-pressure boiling that could lead to vapor locks.
• 🔄 Cross-feed valves and pipes allow fuel to be fed from any tank to any engine, enhancing flexibility and safety in fuel management.
• ♻️ Some aircraft are equipped with fuel dump systems for emergency weight reduction, ensuring the plane can land safely within structural limits.

Q & A

What is the primary function of an aircraft's fuel system?

The primary function of an aircraft's fuel system is to store and deliver fuel to the engine, ensuring it can deliver more fuel than the engine can use during its most critical phase of flight.

How much fuel can a Boeing 747 burn during take-off?

A Boeing 747 can burn as much as 10,000 kilograms per engine per hour during the take-off phase.

What are the different types of fuel tanks used in aircraft?

Aircraft use rigid tanks in wings, integral tanks, center tanks, and sometimes tanks in the fin or stabilizer. These tanks can be used to increase fuel capacity and adjust the aircraft's center of gravity.

What is the purpose of the vent system in aircraft fuel tanks?

The vent system allows air pressure above the fuel in the tank to equalize with ambient pressure, preventing excessive vaporization at altitude and ensuring the fuel system operates correctly.

Why are fuel booster pumps necessary in high-altitude aircraft?

Fuel booster pumps are necessary to prevent bubbles forming due to cavitation or low-pressure boiling at the inlet of the engine-driven fuel pump, which could lead to vapor locks.

How do cross-feed valves work in a multi-engine aircraft's fuel system?

Cross-feed valves allow fuel to be fed from any tank to any engine, ensuring that in case of a pump failure in one tank, fuel can still be supplied to all engines.

What is the purpose of the fuel dump or jettison system in aircraft?

The fuel dump or jettison system is used to reduce the mass of the airplane to its required landing mass when necessary, such as in emergencies or to meet regulatory requirements.

How does the fuel system prevent fuel starvation during flight?

The fuel system prevents fuel starvation by using booster pumps, cross-feed valves, and ensuring the tanks are vented properly to maintain pressure and prevent cavitation.

What is the role of the high-level float switch in the fuel system?

The high-level float switch shuts off fuel to the tank during refueling when the tank is full, preventing overfilling and ensuring the vent system can operate correctly.

How does the aircraft manage fuel imbalance between tanks during flight?

Aircraft manage fuel imbalance by using the cross-feed valve to supply both engines from the tank with more fuel, then adjusting the booster pumps to restore the correct balance.

What is the purpose of the collector tank or surge box in the fuel system?

The collector tank or surge box ensures that the booster pumps are continually submerged in fuel, preventing them from being starved of fuel and keeping them cool.

Outlines

00:00

🛩 Overview of Aircraft Fuel Systems

This paragraph introduces the fundamental purpose of aircraft fuel systems, which is to store and supply fuel to the engines. It emphasizes the necessity for these systems to deliver more fuel than the engine's maximum consumption, especially during critical flight phases. The paragraph provides an example of the Boeing 747's fuel consumption during takeoff. It then describes a simple fuel system in a single-engine light aircraft, explaining the components such as rigid fuel tanks in the wings, refueling mechanisms, fuel pumps, tank selectors, strainers, and priming pumps. The monitoring of the fuel system is also discussed, including level sensors and pressure gauges. The paragraph concludes with a brief mention of more complex fuel systems in multi-engine aircraft, which must handle high-altitude operations and fuel distribution to multiple engines.

05:03

🔧 Components and Subsystems of Multi-Engine Aircraft Fuel Systems

This paragraph delves into the intricacies of fuel systems in multi-engine aircraft, highlighting the challenges posed by high-altitude operations and the need for multiple fuel tanks. It describes integral wing tanks, center tanks, and the use of tanks in the fin or stabilizer not only for fuel capacity but also for adjusting the aircraft's center of gravity. The paragraph explains the function of vent systems to equalize air pressure above the fuel with ambient pressure, the role of vent surge tanks, and the importance of maintaining a minimum free volume in the tanks for the vent system to operate correctly. It also discusses the use of ram air to pressurize tanks during flight, the necessity of fuel booster pumps to prevent cavitation and low-pressure boiling, and the function of non-return valves. The design of feeder boxes to keep booster pumps submerged in fuel is also mentioned, along with the use of filters and screens to protect pumps from debris.

10:04

📡 Fuel System Controls and Operations in Twin-Engine Aircraft

The focus of this paragraph is on the operational aspects of the fuel system in twin-engine aircraft. It details the control panel and schematic fuel system diagram, including selector switches for booster pumps, warning lights for pump failures, and cross-feed valves. The paragraph explains the function of suction valves, temperature sensors, and engine fuel shutoff valves. It also covers the auxiliary power unit's (APU) fuel system, including its shutoff valve and the use of suction bypass valves. The sequence of fuel usage after takeoff is described, with emphasis on the strategy to reduce wing bending stress by using the center tank first. The paragraph also discusses the cross-feed valve's role in balancing fuel between tanks and the importance of following correct procedures to prevent fuel starvation. Additionally, it introduces the concept of extended-range twin-engine operational performance standards (ETOPS) and the modifications in fuel systems to enhance reliability.

15:08

✈️ Advanced Features of Modern Aircraft Fuel Systems

This paragraph discusses advanced features found in modern extended-range aircraft designed for ETOPS operations. It highlights the split center tank, duplicated feed valves for redundancy, and shutoff valves in the fuel lines. The paragraph also mentions the APU's DC electric fuel pump, which can supply fuel to an engine for rapid restart in case of a double engine failure. The discussion includes the necessity of fuel dump or jettison systems in certain aircraft types to meet landing weight restrictions and maintain structural integrity. The paragraph explains the mechanics of the fuel dump system, including dump pumps, master valves, and the automatic stopping of fuel dumping when a predefined reserve quantity is reached. It also outlines the regulations that dictate the minimum fuel quantity post-dump, ensuring the aircraft can still climb and cruise safely.

20:11

💡 Key Points to Remember about Aircraft Fuel Systems

The final paragraph summarizes the key points from the lesson. It emphasizes the use of ram air in the fuel vent system to pressurize tanks and prevent fuel vaporization. It also reiterates the importance of booster pumps, which are 115-volt AC motor-driven centrifugal pumps operating at pressures between 20 and 50 psi, to prevent vapor lock at the engine-driven fuel pump's inlet. The paragraph reminds us of the cross-feed valve's function, allowing fuel to be fed from any tank to any engine, and the correct procedure for using it. Lastly, it touches on the high-level float valve's role in shutting off fuel during refueling when the tank is full and the necessity of fuel dump systems in certain aircraft, which must automatically stop when a defined reserve quantity of fuel is reached.

Keywords

💡Fuel System

A fuel system in aviation is a critical component designed to store and deliver fuel to the aircraft's engines. It must be capable of delivering more fuel than the engine can use, ensuring the engine is never starved of fuel, especially during critical phases of flight. In the context of the video, the fuel system of a Boeing 747 is highlighted, which can consume up to 10,000 kilograms per engine per hour during takeoff.

💡Fuel Tanks

Fuel tanks are the storage compartments in an aircraft where fuel is held. They are typically located in the wings and can be integral to the wing structure or separate rigid tanks. The video mentions that in multi-engine aircraft, fuel tanks may also be located in the center section or even in the fin or stabilizer, serving dual purposes of increasing fuel capacity and adjusting the aircraft's center of gravity.

💡Vent System

The vent system in an aircraft's fuel system allows air pressure above the fuel to equalize with the ambient pressure. This is crucial for preventing excessive vaporization of fuel at high altitudes. The video explains that the vent system includes vent surge tanks at the wingtips to collect any liquid fuel that might enter the vent system and return it to the main tanks.

💡Booster Pumps

Booster pumps are essential in high-altitude aircraft to prevent cavitation or low-pressure boiling at the engine-driven fuel pump inlet. These are typically centrifugal pumps driven by 115-volt AC motors, providing a low pressure of between 20 and 50 psi with a high flow rate. The video emphasizes their importance in ensuring a continuous supply of fuel to the engines, especially during critical flight phases.

💡Cross-Feed Valve

A cross-feed valve allows fuel to be fed from any tank to any engine, which is crucial for maintaining engine operation in the event of a pump failure in one tank. The video script describes the correct procedure for using the cross-feed valve to prevent fuel starvation, emphasizing the importance of opening the valve before turning off booster pumps in the tank with less fuel.

💡Fuel Dump System

The fuel dump or jettison system is required on aircraft where the maximum takeoff weight is significantly higher than the maximum landing weight. This system allows the aircraft to reduce its weight to meet landing requirements or to ensure safe operation within certain regulations. The video mentions that the fuel dump system includes pumps and valves that safely expel fuel from the aircraft.

💡Float Operated Level Sensors

These sensors are used to monitor the fuel content in the tanks. They operate on the principle of a float that moves with the fuel level, sending a signal to indicate the quantity of fuel. The video script mentions that these sensors are simple yet effective in providing pilots with real-time information about the fuel levels in the tanks.

💡Fuel Pressure Gauge

A fuel pressure gauge monitors the operation of the fuel pump, ensuring that the system is functioning correctly and delivering the necessary pressure to the engine. The video script includes the fuel pressure gauge as part of the monitoring systems that help pilots keep track of the fuel system's health.

💡Engine Driven Fuel Pump

This pump is driven by the engine and is responsible for delivering fuel from the tanks to the engine. It is mentioned in the context of the video as a critical component that can be affected by issues like cavitation or low-pressure boiling, which booster pumps help to prevent.

💡Ram Air

Ram air is the air that is forced into the aircraft's systems due to its forward motion. In the context of the video, ram air is used to partially pressurize the fuel tanks, helping to prevent excessive vaporization of fuel at altitude. This is an important aspect of maintaining the efficiency and safety of the fuel system during flight.

💡Fuel Imbalance

Fuel imbalance refers to a situation where the fuel levels in different tanks are uneven, which can affect the aircraft's balance and performance. The video script discusses how to correct fuel imbalance by using the cross-feed valve and adjusting the operation of the booster pumps in the tanks.

Highlights

Aircraft fuel systems are designed to store and deliver fuel to the engine, ensuring it never starves during critical flight phases.

Large jets like the Boeing 747 can burn up to 10,000 kilograms of fuel per engine per hour during take-off.

Simple single-engine aircraft use rigid fuel tanks in the wings, filled through a refueling pipe and cap.

Fuel is drawn from tanks by mechanical or electrical pumps, with a hand-operated selector for tank choice.

Strainers in the fuel system filter out foreign objects and debris before fuel reaches the engine carburetor.

Piston engines may require priming with fuel before starting, using a hand-operated priming pump.

Multi-engine aircraft have more complex fuel systems to handle high altitude operations and multiple engines.

Modern aircraft may feature a center tank and tanks in the fin or stabilizer for increased fuel capacity and center of gravity adjustments.

Vent systems in fuel tanks equalize air pressure above the fuel with ambient pressure, preventing excessive vaporization.

Ram air is introduced into the vent system during flight to pressurize fuel tanks and prevent fuel from boiling at altitude.

Fuel booster pumps in each tank are essential for high altitude aircraft to prevent cavitation and low pressure boiling.

Booster pumps are typically centrifugal, driven by 115 volt AC motors, providing a low pressure with a high flow rate.

Cross-feed valves and pipes allow fuel to be fed from any tank to any engine, enhancing fuel management flexibility.

Fuel tank layout on a typical two-engined aircraft includes split wing tanks with pumps in the intersection to reduce wing bending stress.

Pilot's fuel control panel includes selector switches for each main tank booster pump and associated warning lights.

Fuel dump or jettison systems are required on aircraft where the maximum takeoff weight is significantly higher than the maximum landing weight.

Fuel dump systems must automatically stop when a defined reserve quantity of fuel is reached to ensure safe landing.

The fuel system is monitored using level sensors and fuel pressure gauges for continuous operation and safety.

Transcripts

in this lesson we will look at fuel

distribution systems

the aircraft fuel system is designed to

store and deliver fuel to the engine

fuel system

it must be capable of delivering more

fuel than the engine can possibly use in

its most critical phase of flight so

that the engine is never starved to fill

big jets such as the Boeing 747 can burn

as much as 10,000 kilograms per engine

per hour during the take-off phase

here is a diagram of a simple single

engined light aircraft fuel system

the fuel tanks are rigid tanks fitted in

the wings

they are filled by an open line

refueling pipe through a filler cap on

top of the wing

the fuel is drawn from the tanks by

mechanical or electrical fuel pump

a hand-operated tank selector which

allows the pilot to use the fuel from

either the right

or left tank

or turn off the supply completely

the fuel then passes through a strainer

which filters out any foreign objects

and debris before being delivered to the

engine carburetor

piston engines often need to be primed

with fuel prior to engine start this is

achieved by use of a hand operated

priming pump which takes fuel from the

filter housing and delivers it to the

engine Inlet manifold

the fuel system is monitored for

contents using simple float operated

level sensors

and fuel pump operation is monitored by

a fuel pressure gauge

drain valves allow any water in the fuel

to be removed before flight

Multi engined gas

aircraft have more complex fuel systems

to cope with the extra problems brought

about by high altitude operations the

use of multiple fill tanks and the needs

to feed the fuel to more than one engine

the fuel tanks are usually integral

tanks in the wings

many modern aircraft may also have a

center tank a tank in the center section

torsion box between the wings

some aircraft types also have fuel tanks

in the fin or stabilizer as well as

being used to increase the fuel capacity

this fuel may also be used to change the

position of the aircraft's center of

gravity

there are a number of components and

subsystems common to all multi-engine

aircraft fuel systems we will now look

at these in some detail

the fuel tanks are fitted with a vent

system

the vent system is to allow the air

pressure above the fuel in the tank to

equalize with the ambient pressure

the area's above the fuel in each tank

are connected together by a vent pipe

the ends of the vent pipe terminate in

small vent surge tanks located at each

wingtip

vent surge tanks are vented to the

atmosphere

the vent search tanks

to collect any liquid fuel which might

get into the vent system during unusual

maneuvering or because of over filling

of the fuel tanks

any fuel caught in the vent surge tanks

is returned to the main tanks either by

gravity or by the operation of a pump

some systems have float operated vent

files fitted which closed to prevent

liquid fuel entering the vent system

the ER sir regulations require that when

a fuel tank is full a minimum of two

percent by volume of the tank capacity

is free of fuel to allow the vent system

to operate correctly

if during refueling the fuel reaches

this level then the high level float

switch or volumetric top of unit will

close the refuelling valve

as the aircraft climbs the air pressure

reduces this in turn reduces the

temperature at which the fuel boils

leading to excessive vaporization of the

fuel

to help prevent this excessive

vaporization at altitude and to give a

positive pressure of fuel to the pumps

ram air may be introduced into the vent

system to partially pressurize the tanks

in flight

this is normally done through ducks on

the underside of the wings

fuel booster pumps are normally fitted

in pairs in each tank to pump fuel from

the tank to the engine they are a

necessity in high altitude aircraft to

prevent bubbles forming due to

cavitation or low pressure boiling at

the inlet of the engine driven fuel pump

each pump has a non-return valve

associated with it to prevent fluid

flowing back through the pump to the

tank when the pump is switched off or

has failed

booster pumps are typically centrifugal

pumps driven by 115 volt AC motors

providing a low pressure of between 20

and 50 psi with a high flow rate

there may also be a suction feed pipe to

allow the engine driven fuel pump to

draw fuel from the tank in the event of

a double booster pump failure

in the event of a double booster pump

failure in one main tank the aircraft

emergency and abnormal procedure

checklist will invariably limit the

aircraft to a maximum operating altitude

to prevent fuel starvation due to

cavitation or low pressure boiling

causing vapor locks at the inlet of the

engine driven fuel pump

filters or screens are used to prevent

any debris in the tank being drawn into

the fuel booster pumps

the booster pumps are fitted in a feeder

box in the bottom of the fuel tank this

box is sometimes referred to as a

collector tank or surge box

the feeder box should remain full of

fuel at all fuel levels and aircraft

altitudes

this allows the booster pump to be

continually submerged in fuel thereby

preventing them from being starved of

fuel and keeping them cool

electrically operated engine fuel

shutoff valves or low pressure are

fitted to allow the engine to be

isolated from the fuel supply cross-feed

valves and pipes form a cross feed

manifold which enables fuel to be fed

from any tank to any engine in this

example there are only two fuel tanks so

only one cross feed valve is required

as we have already said many aircraft

have a center fuel tank in this example

the fuel from the center tank is pumped

into the cross feed manifold on both

sides of the cross feed valve

the aircraft may also have a fuel tank

located in the fin or stabilizer

in our typical system shown here the

fuel from this tank is pumped into the

center tank for distribution to the

engines

i level float switches are used to

automatically close the refuel valve

when the tank is full during refueling

while low level float searches are used

to maintain a required a minimum amount

of fuel in the tanks during fuel

jettison or dumping

each fuel tank will have a fill drain at

the lowest point in the tank to allow

water to be drained from it

in the event of the fuel tank being over

pressurized due to a malfunction a

relief valve may be incorporated to

prevent structural damage to the tank

the system is completed with the

addition of a refuel manifold which

allows all the tanks to be pressure

refilled from a single point

shown here is the fuel tank layout on a

typical two engined aircraft

the only difference to what we have seen

so far is that the wing tanks are split

into outer and inner sections

the fuel pumps are in the intersection

the outer section remains full until the

inner has reached a predetermined level

at which point the outer section fuel is

transferred by gravity to the inner

keeping fuel outboard in this manner

helps to reduce wing bending stress

on the screen now is the pilots of fuel

control panel and a schematic fuel

system diagram from a typical

twin-engine passenger jet

the control panel shows selector

switches for each main tank booster pump

accompanied by associated low pressure

warning lights which illuminate if the

pump should fail or be switched off

the center tank pumps also have switches

and warning lights associated with them

suction valves in the main tanks allow

the engine to be fed by gravity or

suctioned by the engine driven pump in

the event of both booster pumps failing

in one tank

there is a control switch and indicator

light for the cross feed valve the light

is illuminated when the cross feed valve

is open

there is a temperature sensor in the

number one tank which will transmit the

fuel tank temperature to an indicator on

the control panel

the engine fuel shutoff valve is closed

by the operation of a fire handle for

that particular engine in some aircraft

it is also opened and closed by the

selection of the fuel switch during the

normal engine start or shutdown

procedure

the fuel valve closed lights illuminate

when the Associated fuel valve is closed

the auxiliary power unit or APU takes

its fuel from the number one tank via a

suction bypass valve

if there are no booster pumps operating

but it can be fed from any tank if a

booster pump in that tank is selected on

the APU shutoff valve is typically

operated by the APU automatic start or

stop sequence

there are indicators which illuminate

when they're associated low-pressure

fuel filter bypass valve opens due to a

filter blockage this filter is

downstream of the fuel heater

feel from a pressure refueling system is

fed in at the refueling station and

dispensed to the fuel tanks as required

defueling is achieved by opening the

manual defueling valve the booster pumps

can then be used to pump fuel into a

tanker

the normal sequence of fuel usage after

takeoff would be to use the center fuel

tank first followed by the wing tank

fuel

this sequence again helps to relieve the

wing bending stress

the operation is achieved

semi-automatically

by switching on all tank booster pumps

since the center tank pumps operate at a

higher pressure than the main tank pumps

fuel is used from the center tank first

when it's booty pumps can no longer pump

fuel from the center tank any remaining

fuel can be moved to the number one tank

by operation of the center tank scavenge

jet pump

the main tanks will now feed their

respective engines

the cross feed valve allows both engines

to be fed from one wing fuel tank

or one engine to be fed from both wing

tanks

fuel imbalance in flight between the

number1 and number2 tank can be

corrected

by opening the cross-feed valve

and then switching off the pumps in the

tank with less fuel until the correct

balance is achieved by supplying both

engines from the tank with more fuel

it is important that this secrets is

followed exactly as there is a danger of

starving an engine of fuel

if their fuel pumps are switched off

before the cross feed valve is opened

when the correct balance is achieved

their previously switched off booster

pumps are switched on again first

and then the cross feed valve is closed

again it is important that this sequence

is followed this will restore what is

known as tank to engine configuration

that is number one tank feeding number

one engine and number two tank feeding

number two engine

you

this diagram shows the fuel system from

a modern extended range 24 ment

standards or etops aircraft

it is very similar to our previous

system apart from a few additions to

improve its reliability

the center tank is split into two parts

but it operates at all times as a single

tank

feed valve is duplicated to provide

redundancy normally both valves move

together as one

shutoff valves in the fuel line to the

engine

our valve shuts off the fuel as it

leaves the tank system

engine fuel shutoff valve shuts off the

fuel at the engine firewall

the APU has a DC electric fuel pump

which will switch on automatically if

the APU is operated with no booster

pumps operating

this pump will also automatically start

and the APU isolation valve will open to

allow the DC pump to supply fuel to the

left engine for rapid restarting in the

event of a double engine failure

some aircraft types have a fuel dump or

jettison system fitted

this system is required if the maximum

landing mass of the aircraft is

significantly less than the maximum

takeoff mass and landing at the higher

mass would compromise the structural

integrity of the aircraft or if the

aircraft cannot satisfy the discontinued

approach climb gradients required by the

AR sir regulations at its maximum

takeoff mass

in an emergency fuel can be dumped to

reduce the mass of the airplane to its

required landing mask

the fuel dump system consists of fuel

dump pumps in each of the tanks from

which the fuel is to be dumped

connected by pipes to fuel dump master

valves and dump outlets

typically there will be a dump master

valve on each wing at the outboard

trailing edge to enable the fuel to be

dumped safely with no danger of it

entering the aircraft or any of its

systems

on older aircraft fuel dumping is

controlled from the pilots or flight

engineers fuel control panel

on modern aircraft the pilot has a

selector knob which allows him to select

the amount of fuel to be dumped or the

amount of fuel to remain

the fuel dumping process will be

automatically stopped when this level

has been reached

if operation of the flaps or slats will

cause the fuel being dumped to impinge

on the airframe a placard must be

displayed warning the pilot not to

operate the flaps or slats during fuel

dumping operations

would be clearly undesirable to dump all

of the fuel in the aircraft and

safeguards must be in place to allow a

minimum amount of fuel to remain

er sir regulations stipulate that the

minimum amount of fuel remaining after

dumping must be sufficient to enable the

aircraft to climb to 10,000 feet

and thereafter allow 45 minutes cruise

at a speed for maximum range

this minimum fuel quantity is calculated

at the design stage and the low-level

float switches in the main tanks are

calibrated to stop the fuel dump if this

level is reached

that is the end of the lesson here are

the main points you should remember

the fuel vent system uses ram air to

pressurize the fuel tanks to help

prevent vaporization of the fuel

to feel booster pumps our 115 volt AC

motor driven centrifugal pumps

and they operate our pressures of

between 20 and 50 psi

their purpose is to supply a head of

pressure to the engine driven fuel pumps

in order prevent cavitation or low

pressure boiling causing a vapor lock

at the inlet to the engine driven fuel

pump

the booster pumps are fitted in a

collector tank or feeder box or surge

box in the bottom of the fuel tank this

allows the booster pumps to be

continually submerged and fuel thereby

preventing them from being starved of

fuel and keeping them cool

the cross feed valve or valves allow the

fuel to be fed from any tank to any

engine

remember that when commencing cross

feeding the cross feed valve is opened

before the booster pumps in the low tank

are turned off

when cross feeding is complete the pumps

are turned back on before the cross feed

valve is closed

the purpose of the high-level float

valve is to shut off fuel to the tank

during refueling when the tank is full

fuel dump or jettison systems are

required on aircraft types where the

maximum takeoff weight is significantly

higher than the maximum landing weight

the fuel dump system must automatically

stop dumping fuel when a defined reserve

quantity of fuel is reached