Aircraft Fuel & Fuel Metering Systems: How Aircraft Engines Get the Right Fuel at the Right Time

An aircraft engine can have perfect compression, a strong ignition system, and plenty of airflow, but none of that matters if the engine does not receive the correct amount of fuel at the correct time.

That is the job of the aircraft’s fuel and fuel metering system.

At first glance, the purpose of a fuel system seems simple: move fuel from the aircraft’s fuel tanks to the engine. In reality, the system has to do much more than simply deliver fuel.

It must supply fuel reliably during changes in:

• Engine power
• Altitude
• Air density
• Aircraft attitude
• Temperature
• Atmospheric pressure
• Acceleration and deceleration
• Fuel demand

The fuel metering system then has another critical job: determining how much fuel the engine actually needs.

For reciprocating engines, this generally means producing the correct fuel-air mixture for combustion. For turbine engines, fuel controls must schedule fuel flow according to engine operating conditions while preventing conditions such as compressor stall, excessive turbine temperature, flameout, or overspeed.

Understanding fuel metering becomes much easier when the entire system is viewed as a chain:

Fuel tank → fuel supply system → fuel metering system → induction/combustion system → engine power

This article explores how that chain works.

Primary FAA Reference:
Aviation Maintenance Technician Handbook—Powerplant, FAA-H-8083-32B, Chapter 2, Engine Fuel & Fuel Metering Systems
Federal Aviation Administration

1. What Does an Aircraft Fuel System Have to Do?

The basic requirement of an engine fuel system is straightforward:

Supply the engine’s fuel metering device with an adequate supply of fuel during all operating conditions.

That sounds simple until we consider the environment in which an aircraft operates.

An automobile normally stays close to sea level and relatively upright. An aircraft may climb from sea level to thousands of feet within minutes while experiencing major changes in atmospheric pressure, temperature, acceleration, and engine power.

The fuel system must continue operating correctly through all of those conditions.

According to the FAA’s Aviation Maintenance Technician Handbook—Powerplant, the engine fuel system must supply fuel to the engine’s metering device during all conditions of ground and air operation.

The system must therefore provide:

1. Adequate fuel quantity
2. Adequate fuel pressure
3. Proper fuel filtration
4. Reliable fuel flow
5. Protection against vapor formation
6. Proper fuel metering
7. Correct fuel distribution

The exact design depends heavily on the aircraft and engine.

A small, high-wing reciprocating-engine airplane may use a relatively simple gravity-feed system.

A large multiengine aircraft may contain:

• Multiple fuel tanks
• Boost pumps
• Transfer pumps
• Crossfeed systems
• Fuel heaters
• Fuel filters
• Fuel control units
• Fuel flow transmitters
• Electronic engine controls
• Automatic fuel management systems

Despite the difference in complexity, the basic goal remains the same:

Get clean fuel to the engine at the pressure and flow rate the engine requires.

2. Aviation Gasoline and Jet Fuel

Aircraft engines primarily use two broad categories of fuel:

The fuels are not interchangeable.

They have different volatility characteristics, combustion properties, operating environments, and fuel-system requirements.

3. Aviation Gasoline — AVGAS

Reciprocating aircraft engines commonly use aviation gasoline, usually called AVGAS.

One of the most common grades in general aviation is:

100LL

The “100” refers to the fuel’s anti-knock performance rating, while “LL” means:

Low Lead

However, “low lead” is somewhat misleading by modern standards. The term means lower lead content relative to older high-lead aviation fuels—not that the fuel contains only a tiny amount of lead.

100LL is normally identified by its blue color.

Older AVGAS grades historically used different colors so that fuel type could be identified visually.

Fuel identification is extremely important because using the wrong fuel can cause severe engine damage or engine failure.

4. Why Octane Rating Matters

Inside a reciprocating aircraft engine, the fuel-air mixture should burn in a controlled manner after ignition by the spark plugs.

One dangerous abnormal combustion condition is detonation.

Detonation occurs when portions of the fuel-air charge burn explosively rather than through the normal controlled flame-front process.

Detonation can produce extremely high cylinder pressures and temperatures.

Possible consequences include:

• Piston damage
• Valve damage
• Cylinder-head damage
• Excessive cylinder temperature
• Loss of engine power
• Complete engine failure

Higher-performance engines generally require fuels with greater resistance to detonation.

That resistance is one reason the fuel grade specified by the aircraft and engine manufacturer must always be used.

5. Turbine Engine Fuel

Gas turbine engines typically use kerosene-based aviation fuels.

A common example is:

Jet A

Jet A is generally clear to straw-colored and has very different characteristics from aviation gasoline.

Turbine engines operate with continuous combustion rather than the intermittent combustion cycles of reciprocating engines.

Fuel is continuously sprayed into the combustion section where it mixes with compressed air and burns.

The turbine fuel system must therefore provide a carefully controlled and continuous supply of fuel over an enormous operating range.

6. The Fuel-Air Mixture

For a reciprocating engine to produce power, fuel must be mixed with air before combustion.

The relationship between the amount of fuel and air is called the:

Fuel-air ratio

If there is too much fuel relative to the amount of air, the mixture is:

Rich

If there is too little fuel relative to the amount of air, the mixture is:

Lean

Neither extreme is desirable.

The engine requires a mixture that supports combustion while also providing the desired combination of:

• Power
• Cooling
• Fuel economy
• Smooth operation

7. Rich Mixtures

A rich mixture contains more fuel relative to air.

Rich mixtures are commonly used during high-power operations.

Why?

Because not all of the additional fuel is necessarily needed solely for combustion.

Some of the excess fuel helps absorb heat and can contribute to engine cooling.

This becomes especially important during high-power conditions such as:

• Takeoff
• Initial climb
• High-power operation

Running excessively lean under high power can increase combustion temperatures and may contribute to detonation or engine damage.

8. Lean Mixtures

A lean mixture contains less fuel relative to the amount of air.

Leaning can reduce fuel consumption and improve efficiency when performed according to the aircraft and engine manufacturer’s procedures.

This becomes particularly important as altitude increases.

As an aircraft climbs, atmospheric density decreases.

That means each intake stroke brings less mass of air into the engine.

If fuel flow remained unchanged, the mixture would progressively become richer.

Therefore, many reciprocating aircraft engines provide a way to reduce fuel flow as altitude increases.

This is the purpose of the:

Mixture control

9. Why Mixture Control Is Necessary

Imagine an engine operating at sea level.

The carburetor or fuel injection system meters fuel for the amount of air entering the engine.

Now climb several thousand feet.

Air density decreases.

The engine is now receiving less oxygen even if the throttle position remains similar.

If the same amount of fuel continues to be supplied, there is too much fuel for the available air.

The mixture becomes excessively rich.

Possible symptoms include:

• Reduced power
• Rough operation
• Increased fuel consumption
• Spark plug fouling
• Incomplete combustion

Leaning restores the appropriate relationship between fuel and air.

10. Fuel Metering Systems

The device responsible for controlling the amount of fuel delivered to the engine is called the:

Fuel metering system

On reciprocating aircraft engines, two major types are commonly encountered:

1. Carburetor systems
2. Fuel injection systems

Each accomplishes essentially the same basic task:

Meter fuel in proportion to the airflow entering the engine.

They simply accomplish it differently.

11. The Float-Type Carburetor

The float-type carburetor is one of the classic aircraft fuel metering systems.

Its basic operating principle depends on pressure differences.

Air entering the carburetor passes through a narrowed section called the:

Venturi

As air moves through the venturi, its velocity increases.

At the same time, its static pressure decreases.

This creates a pressure difference between the carburetor’s float chamber and the venturi throat.

That pressure difference causes fuel to flow through the discharge nozzle into the incoming airflow.

The fuel mixes with the air and continues into the engine.

12. The Venturi Principle

The venturi is one of the most important concepts to understand when studying carburetors.

The basic relationship is:

Smaller passage → higher air velocity → lower static pressure

That lower pressure is what helps draw fuel from the discharge nozzle.

A simplified flow looks like this:

Incoming Air
     ↓
     ↓
 ┌───────────┐
 │           │
 │   \   /   │
 │    \ /    │
 │     V     │  ← Venturi
 │    / \    │
 │   /   \   │
 │           │
 └───────────┘
       ↓
   Engine

Fuel is discharged near the low-pressure region of the venturi.

The faster the airflow through the carburetor, the greater the pressure difference available for fuel metering.

13. The Float Chamber

The carburetor needs a relatively constant supply of fuel available for metering.

This is accomplished by the:

Float chamber

Inside the chamber is a float connected to a needle valve.

As the fuel level drops:

1. The float drops.
2. The needle valve opens.
3. More fuel enters the chamber.

As the fuel level rises:

1. The float rises.
2. The needle valve moves toward its seat.
3. Fuel entering the chamber is reduced or stopped.

The concept is similar to the float valve found in many other fluid-level control systems.

Maintaining the correct fuel level is critical because the metering system depends on a predictable relationship between fuel level and venturi pressure.

14. The Main Metering System

During normal operation above idle, fuel generally flows through the carburetor’s main metering system.

The system must provide approximately the correct amount of fuel for the amount of airflow entering the engine.

As throttle opening increases:

• Airflow increases
• Venturi pressure decreases
• Fuel discharge increases

This allows fuel flow to increase as engine power increases.

15. Why a Carburetor Needs More Than One Fuel Circuit

A simple venturi and discharge nozzle cannot provide the ideal fuel-air ratio under every operating condition.

An aircraft engine operates across a very wide range:

• Starting
• Idle
• Taxi
• Acceleration
• Cruise
• Full power
• Rapid throttle movement

Because of this, carburetors incorporate additional systems.

These may include:

• Idle system
• Main metering system
• Mixture control
• Accelerating system
• Economizer or power enrichment system

Each exists because the basic main metering system alone cannot perfectly handle every operating condition.

16. The Idle System

When the throttle is nearly closed, airflow through the main venturi is very low.

That means the pressure difference at the main discharge nozzle may not be sufficient to meter fuel properly.

The engine still needs fuel to run.

Therefore, the carburetor uses a separate:

Idle system

Fuel is discharged through an idle passage near the throttle valve where sufficient pressure difference exists to provide fuel flow.

This allows the engine to continue operating at low RPM.

17. Idle Mixture Adjustment

The idle system usually includes a means of adjusting the idle fuel-air mixture.

This adjustment is important.

If the idle mixture is too rich, the engine may:

• Run rough
• Foul spark plugs
• Load up during extended idle
• Consume excessive fuel

If the mixture is too lean, the engine may:

• Hesitate
• Run rough
• Stop when the throttle is reduced

Idle mixture adjustments should always be made according to the applicable manufacturer’s maintenance instructions.

18. The Accelerating System

Suppose the throttle is opened rapidly.

Airflow can increase almost immediately.

Fuel, however, has greater mass and inertia than air and may not respond at exactly the same rate.

The result could temporarily be a mixture that is too lean.

A lean mixture during rapid acceleration can cause:

• Hesitation
• Roughness
• Backfiring
• Engine stoppage

To prevent this, many carburetors use an:

Accelerating pump

The accelerating pump supplies an additional quantity of fuel when the throttle is opened rapidly.

Think of it as a temporary shot of extra fuel used to bridge the transition between low and high airflow.

19. The Economizer System

At high power, an aircraft engine often requires a richer mixture than it needs during normal cruise.

The carburetor therefore may use an:

Economizer system

The economizer provides additional fuel during high-power operation.

Despite the name, its purpose is not simply to make the engine more economical at that moment.

Instead, it allows the engine to operate relatively economically during lower-power operation while still providing the richer mixture required at high power.

This is an important troubleshooting area.

If the economizer system fails to operate correctly, mixture and engine performance problems can result.

20. Mixture Control in a Carburetor

The cockpit mixture control allows the pilot to control the amount of fuel entering the metering system.

Typical positions include:

• Full rich
• Leaned positions
• Idle cutoff

At idle cutoff, fuel flow is stopped so the engine can be shut down.

The exact mechanism varies by carburetor design.

For maintenance technicians, it is important to understand that mixture control is not simply a cockpit lever—it is mechanically or electronically connected to a fuel-metering mechanism that must be rigged and adjusted correctly.

21. Carburetor Icing

One of the most important characteristics of a carburetor is its susceptibility to icing.

Carburetor ice can form because of two major cooling effects:

1. Pressure reduction through the venturi
2. Fuel vaporization

Both processes lower the temperature inside the carburetor.

Under the right atmospheric conditions, the temperature can drop enough for moisture in the air to freeze.

Ice commonly forms around the:

• Venturi
• Throttle plate

As ice accumulates, airflow becomes restricted.

Engine power decreases.

If enough ice forms, the engine can eventually stop.

22. Carburetor Heat

Aircraft equipped with carburetors commonly have a:

Carburetor heat system

Carburetor heat routes warmer air into the carburetor.

This helps melt existing ice and prevent additional accumulation.

However, warm air is less dense than cold air.

Therefore, applying carburetor heat normally causes some reduction in engine power.

The important maintenance lesson is that carburetor heat involves both the fuel metering and induction systems.

A malfunctioning carburetor heat valve, duct, control cable, or air box can affect engine operation.

23. Pressure Carburetors

Float carburetors work well in many applications, but they have limitations.

Aircraft maneuvering and attitude changes can affect the behavior of fuel in a float chamber.

More advanced engines therefore may use:

Pressure carburetors

Pressure carburetors meter fuel under pressure rather than depending on a conventional float chamber in the same manner as a basic float-type carburetor.

They provide more reliable fuel metering during varying aircraft attitudes and operating conditions.

Pressure carburetion also helped lead toward the widespread use of aircraft fuel injection systems.

24. Fuel Injection

Instead of mixing fuel and air inside a conventional carburetor, many reciprocating aircraft engines use:

Fuel injection

A fuel injection system meters fuel and distributes it to the engine under pressure.

A typical continuous-flow aircraft fuel injection system may contain:

• Engine-driven fuel pump
• Fuel-air control unit
• Fuel metering section
• Fuel manifold valve
• Individual fuel discharge nozzles

Fuel is delivered to each cylinder through separate fuel lines.

25. Basic Fuel Injection Flow

A simplified system looks like this:

Fuel Tank
    ↓
Fuel Pump
    ↓
Fuel-Air Control Unit
    ↓
Fuel Metering Section
    ↓
Fuel Manifold / Flow Divider
    ↓
Individual Fuel Lines
    ↓
Injector Nozzles
    ↓
Engine Cylinders

Each component has a specific job.

The pump provides pressure.

The metering section determines fuel quantity.

The manifold divides the fuel.

The nozzles introduce the fuel into the induction airflow near the cylinders.

26. Fuel-Air Control Unit

The fuel-air control unit senses or responds to airflow through the engine.

As airflow changes, the system adjusts fuel flow.

The goal remains the same as with a carburetor:

Maintain an appropriate relationship between airflow and fuel flow.

The difference is how the fuel is delivered.

Instead of drawing fuel from a float bowl using venturi suction, the injection system supplies fuel under pressure.

27. Fuel Manifold Valve

After fuel has been metered, it must be distributed to the cylinders.

This is commonly accomplished by a:

Fuel manifold valve

It may also be referred to as a:

Flow divider

Its purpose is to distribute metered fuel to the individual injector lines.

From there, fuel travels to the discharge nozzle at each cylinder.

28. Fuel Injection Nozzles

Each cylinder has a fuel discharge nozzle.

The nozzle introduces fuel into the induction airflow near the cylinder’s intake port.

Proper nozzle operation is extremely important.

A partially restricted nozzle can cause one cylinder to operate lean while the others operate normally.

Possible symptoms include:

• Rough engine operation
• Uneven exhaust gas temperatures
• Reduced power
• Abnormal cylinder temperatures

This is why fuel nozzle inspection and cleaning can be important during troubleshooting.

29. Advantages of Fuel Injection

Fuel injection offers several advantages compared with a conventional float carburetor.

Depending on the system, these can include:

• More uniform fuel distribution
• Improved fuel metering
• Reduced susceptibility to carburetor icing
• Better operation during maneuvering
• Improved engine efficiency
• More precise mixture control

However, fuel injection introduces its own maintenance concerns.

Examples include:

• Contaminated nozzles
• Fuel pressure problems
• Incorrect rigging
• Fuel leaks
• Flow divider problems
• Pump problems
• Improper mixture adjustment

No system eliminates maintenance—it simply changes the components that require attention.

30. Vapor Lock

One of the most important fuel-system problems is:

Vapor lock

Aircraft fuel systems are designed to keep fuel in a liquid state until it reaches the location where it is intended to be vaporized or atomized.

However, fuel can sometimes vaporize prematurely inside:

• Fuel lines
• Pumps
• Fuel-system components

The resulting vapor bubbles interfere with normal liquid fuel flow.

This condition is called vapor lock.

31. What Causes Vapor Lock?

The FAA identifies three general contributors to vapor lock:

1. Low fuel pressure
2. High fuel temperature
3. Excessive fuel turbulence

These conditions make it easier for fuel to vaporize.

32. Altitude and Vapor Lock

As altitude increases, atmospheric pressure decreases.

Lower pressure reduces the boiling point of a liquid.

Therefore, fuel that remains liquid at sea-level pressure may become more likely to form vapor at altitude.

This is especially significant when the fuel is already warm.

Imagine an aircraft sitting on a ramp during a hot summer day.

The fuel becomes warm.

Shortly after takeoff, the aircraft climbs rapidly.

Atmospheric pressure decreases much faster than the fuel temperature.

That combination can encourage vapor formation.

33. Fuel Temperature and Vapor Formation

Heat from the engine compartment can also warm fuel lines and fuel-system components.

High temperature combined with low pressure creates favorable conditions for vapor formation.

Fuel lines must therefore be routed and protected appropriately.

Fuel-system design may also incorporate boost pumps or other methods to maintain adequate pressure and reduce vapor formation.

34. Fuel Turbulence

Fuel does not always flow smoothly.

Turbulence may result from:

• Sharp bends
• Sudden changes in line direction
• Fuel sloshing
• Pump action
• Restrictions

Turbulence can release dissolved air and encourage vapor formation.

This is one reason proper fuel-line routing is important.

A fuel line is not simply installed wherever it happens to fit.

Its routing can affect system performance.

35. Fuel Pumps

Aircraft may use several types of fuel pumps.

Common examples include:

• Engine-driven fuel pumps
• Electric boost pumps
• Auxiliary pumps
• Transfer pumps

The specific arrangement depends on aircraft design.

The engine-driven pump generally provides the fuel pressure required during normal engine operation.

An electric boost pump may be used for purposes such as:

• Engine starting
• Takeoff
• Landing
• Priming
• Vapor suppression
• Backup fuel pressure

The exact operating procedure depends on the aircraft.

36. Why Fuel Pressure Matters

Fuel metering systems are designed to operate within specific pressure ranges.

Too little fuel pressure can cause:

• Fuel starvation
• Lean operation
• Power loss
• Engine stoppage

Excessive fuel pressure can also create problems by affecting metering and component operation.

This is why fuel pressure is often an important diagnostic measurement.

When troubleshooting a fuel-system problem, technicians should not simply ask:

“Is fuel reaching the engine?”

The better question is:

“Is fuel reaching the metering system at the correct pressure and flow rate?”

37. Fuel Filters and Strainers

Aircraft fuel systems contain filters or strainers designed to prevent contaminants from reaching sensitive components.

Contamination may include:

• Dirt
• Rust
• Tank debris
• Seal material
• Water
• Foreign particles

A partially restricted filter can reduce fuel flow enough to cause engine problems even though fuel is still technically reaching the engine.

This is why inspection of strainers and filters can provide valuable troubleshooting information.

38. Water Contamination

Water is especially dangerous in aircraft fuel systems.

It can enter through:

• Condensation
• Contaminated fuel supplies
• Poorly sealed fuel caps
• Rainwater intrusion

Because water and aviation fuel have different densities, water may collect at low points in the fuel system.

Aircraft therefore commonly have fuel drains or sumps located at these points.

Fuel samples should be inspected for:

• Water
• Sediment
• Incorrect fuel
• Other contamination

39. Turbine Engine Fuel Metering

Fuel metering becomes considerably more complex in a gas turbine engine.

A turbine engine must receive the correct amount of fuel over a wide range of operating conditions.

Too little fuel can result in:

• Flameout
• Poor acceleration
• Insufficient thrust

Too much fuel can result in:

• Excessive turbine temperature
• Compressor stall
• Rich blowout
• Engine damage

The fuel control must therefore carefully schedule fuel flow.

40. What Does “Fuel Scheduling” Mean?

When discussing turbine engines, the term fuel scheduling is commonly used.

Fuel scheduling means determining the amount of fuel that should be delivered based on engine operating conditions.

The fuel control may consider parameters such as:

• Throttle position
• Compressor speed
• Compressor inlet pressure
• Compressor discharge pressure
• Temperature
• Engine RPM
• Other engine operating variables

The exact inputs depend on the engine and fuel-control design.

41. Hydromechanical Fuel Controls

Traditional turbine engines often use:

Hydromechanical fuel controls

These systems use combinations of:

• Fuel pressure
• Springs
• Diaphragms
• Bellows
• Valves
• Flyweights
• Mechanical linkages

to calculate and control fuel flow.

These devices are remarkable because they can perform complex fuel scheduling without a digital computer.

However, they contain precision components and require specialized maintenance procedures.

42. Electronic Engine Controls

Modern engines increasingly use electronic control systems.

Electronic engine controls receive information from sensors throughout the engine.

A computer then calculates the required fuel flow and commands the fuel metering system accordingly.

The FAA notes that electronic engine controls have significantly improved the ability of fuel systems to accurately schedule fuel.

Instead of relying solely on mechanical relationships, the system can continuously evaluate engine operating conditions.

43. FADEC

The most advanced form of electronic engine management is:

FADEC — Full Authority Digital Engine Control

A FADEC system provides comprehensive electronic control of engine operation.

Rather than the pilot directly controlling fuel flow through a mechanical linkage, the pilot commands a desired engine operating condition.

The FADEC determines how to achieve it.

Conceptually:

Pilot Command
      ↓
     FADEC
      ↓
Engine Sensors ─────→ Computer Logic
      ↑                    ↓
      └──────── Engine ← Fuel Metering

The computer continuously monitors engine conditions and adjusts fuel flow.

44. Why FADEC Is Important

FADEC can provide several advantages:

• Precise fuel scheduling
• Improved engine efficiency
• Reduced pilot workload
• Engine limit protection
• Improved starting
• Improved acceleration control
• More consistent engine operation

For maintenance technicians, however, electronic control changes the troubleshooting process.

Instead of examining only mechanical components, technicians may also need to evaluate:

• Sensors
• Electrical wiring
• Connectors
• Electronic control units
• Fault codes
• Data buses
• Actuators

Modern fuel-system troubleshooting is increasingly a combination of mechanical and electronic diagnostics.

45. Turbine Fuel Nozzles

After turbine fuel has been metered, it must enter the combustion chamber in a form that can burn efficiently.

This is the job of the:

Fuel nozzle

Fuel nozzles atomize fuel into a fine spray.

Atomization is extremely important.

A large stream of liquid fuel does not mix with compressed air as effectively as a fine mist.

Good atomization promotes:

• Efficient combustion
• Stable flame
• Even temperature distribution
• Reliable engine operation

46. Primary and Secondary Fuel Flow

Some turbine fuel nozzles use multiple flow passages or stages.

At lower fuel pressures, one passage may provide the necessary spray pattern.

As fuel pressure increases, additional passages may begin flowing.

This helps maintain good fuel atomization over a large operating range.

The exact design varies by engine and nozzle type.

47. Fuel Manifolds

Turbine engines commonly use fuel manifolds to distribute fuel around the combustion section.

The goal is to provide approximately uniform fuel flow to the various fuel nozzles.

Uneven fuel distribution can create uneven combustion temperatures.

This is especially important because turbine components operate at extremely high temperatures.

Localized hot spots can damage:

• Combustion liners
• Turbine nozzle guide vanes
• Turbine blades

Proper fuel distribution is therefore directly related to turbine durability.

48. Turbine Engine Starting

Fuel metering is especially critical during turbine-engine starting.

During start, the engine is turning relatively slowly.

Airflow through the compressor is limited.

If too much fuel is introduced for the available airflow, turbine temperature can rise rapidly.

This can produce a:

Hot start

A hot start occurs when engine temperature exceeds allowable limits during the starting sequence.

Possible causes may involve:

• Excessive fuel
• Insufficient starter speed
• Inadequate airflow
• Incorrect starting procedure
• Fuel-control problems

49. Hung Starts

Another abnormal turbine start condition is a:

Hung start

During a hung start, the engine lights off but fails to accelerate normally to idle RPM.

The engine effectively becomes “hung” at a lower-than-normal speed.

Possible causes can involve:

• Insufficient starter performance
• Fuel scheduling problems
• Mechanical drag
• Compressor problems

Understanding the interaction between fuel flow and compressor airflow is critical when diagnosing turbine starting problems.

50. No-Light-Off Conditions

A turbine engine may also fail to light during start.

Possible causes can include:

• No fuel
• Insufficient fuel
• Ignition problems
• Fuel nozzle problems
• Fuel-control problems

This illustrates an important troubleshooting principle:

Do not immediately assume that a failure to start is an ignition problem.

Combustion requires:

1. Air
2. Fuel
3. Ignition

A problem with any one of these can prevent engine start.

51. Troubleshooting Fuel Metering Systems

Fuel-system troubleshooting should always follow the manufacturer’s procedures.

However, understanding system theory makes those procedures much easier to follow.

When an engine runs poorly, ask a sequence of questions.

Is fuel reaching the engine?

Check:

• Fuel quantity
• Fuel selector position
• Shutoff valves
• Fuel pumps
• Filters
• Fuel lines

Is fuel pressure correct?

Check:

• Pump output
• Restrictions
• Leaks
• Pressure indications

Is fuel being metered correctly?

Check:

• Carburetor
• Fuel control
• Fuel injection servo
• Mixture control
• Fuel control rigging

Is fuel being distributed correctly?

Check:

• Flow divider
• Fuel manifold
• Injector lines
• Fuel nozzles

Breaking the system into sections makes troubleshooting far more systematic.

52. Troubleshooting an Engine That Will Not Idle

Suppose a reciprocating engine operates reasonably well at higher RPM but will not idle correctly.

That immediately provides useful information.

If the engine runs at higher power, the main fuel supply is probably capable of delivering at least some fuel.

Attention can then shift toward systems used specifically at low power.

Possible areas include:

• Idle fuel passages
• Idle mixture adjustment
• Throttle adjustment
• Induction leaks
• Carburetor contamination
• Fuel pressure
• Metering-system problems

This is why understanding the individual circuits inside a carburetor is more useful than simply memorizing component names.

53. Troubleshooting Acceleration Problems

Now suppose the engine idles normally but hesitates when the throttle is opened rapidly.

That points toward a different area.

Remember what happens during acceleration:

Airflow increases quickly.

Fuel flow must increase with it.

If fuel delivery momentarily falls behind airflow, the mixture becomes lean.

Therefore, an acceleration problem may lead the technician to inspect the:

Accelerating system

Again, system theory guides troubleshooting.

54. Troubleshooting High-Power Problems

Suppose the engine operates normally at low and medium power but performs poorly at high power.

Now consider the systems that become particularly important at high power.

Possible areas include:

• Main metering system
• Fuel pressure
• Fuel flow
• Economizer/power enrichment system
• Fuel pump
• Restricted filters
• Induction airflow

The symptoms tell you where in the system to begin looking.

55. Why Maintenance Manuals Matter

The FAA Powerplant handbook provides excellent explanations of operating principles.

However, it is not a replacement for the manufacturer’s maintenance information.

Actual maintenance should use the applicable:

• Aircraft maintenance manual
• Engine maintenance manual
• Component maintenance manual
• Service instructions
• Service bulletins
• Airworthiness directives
• Approved technical data

The FAA handbook itself emphasizes that its generalized explanations should be supplemented by manufacturer information and are not intended to supersede official regulations or manufacturer instructions.

That distinction is extremely important for an A&P mechanic.

The FAA handbook helps you understand how the system works.

The manufacturer’s documentation tells you how to maintain that specific system.

56. A Simple Way to Remember Fuel Metering

When studying fuel systems, remember four words:

Supply → Meter → Distribute → Burn

Supply

Get fuel from the tank to the engine.

Meter

Determine how much fuel the engine needs.

Distribute

Send the fuel where it needs to go.

Burn

Mix the fuel with air and produce controlled combustion.

Almost every fuel-system component fits somewhere within those four steps.

57. Carburetor vs. Fuel Injection

Here is a simplified comparison:

Neither system changes the fundamental requirement:

Fuel flow must correspond to airflow and engine operating conditions.

58. Reciprocating vs. Turbine Fuel Metering

The biggest conceptual difference is what the fuel system is trying to accomplish.

Reciprocating Engine

The system primarily meters fuel to establish the proper:

Fuel-air mixture

Turbine Engine

The system schedules fuel flow to provide the desired engine operation while remaining within engine limitations.

A turbine fuel control therefore needs to account for much more than simply throttle position.

It may need to control fuel during:

• Starting
• Idle
• Acceleration
• Deceleration
• Cruise
• Maximum power
• Altitude changes

while simultaneously protecting the engine.

59. Key Terms for A&P Students

If you are studying aircraft fuel systems, make sure you can explain these terms without simply memorizing a definition:

AVGAS
Aviation gasoline used primarily in reciprocating aircraft engines.

Jet A
Kerosene-based fuel commonly used in turbine-powered aircraft.

Fuel-air ratio
The relationship between fuel and air entering the combustion process.

Rich mixture
A mixture containing relatively more fuel.

Lean mixture
A mixture containing relatively less fuel.

Venturi
A narrowed passage that increases fluid velocity and decreases static pressure.

Float chamber
A carburetor chamber that maintains a controlled fuel level.

Main metering system
The carburetor circuit supplying fuel during normal operating ranges.

Idle system
A fuel circuit that provides fuel when airflow through the main venturi is insufficient.

Accelerating pump
A device that temporarily supplies additional fuel during rapid throttle opening.

Economizer
A carburetor system that provides the richer mixture required during high-power operation.

Mixture control
A control used to adjust the amount of fuel relative to airflow.

Vapor lock
Interruption or restriction of fuel flow caused by premature fuel vaporization.

Fuel injection
A system that meters and supplies fuel under pressure rather than through a conventional float carburetor.

Flow divider
A device that distributes metered fuel to individual cylinders.

Fuel nozzle
A device that introduces and atomizes fuel into the engine airflow.

Fuel scheduling
Controlling turbine-engine fuel flow according to engine operating conditions.

FADEC
Full Authority Digital Engine Control; an electronic system that controls engine operation, including fuel scheduling.

60. FAA Powerplant Test Prep: 50 Possible Fuel-System Questions

The following are study questions written from FAA Powerplant fuel-system concepts. They are not presented as verbatim FAA knowledge-test questions. They are designed around the FAA Aviation Mechanic Powerplant ACS subject area Engine Fuel and Fuel Metering Systems (AM.III.I) and FAA-H-8083-32B, Chapter 2.

Try answering each question before reading the answer and explanation.

Question 1

What is the primary purpose of an engine fuel metering system?

A. To maintain constant fuel pressure regardless of engine demand
B. To meter the proper quantity of fuel for the amount of air entering the engine
C. To maintain a constant fuel level in the aircraft tanks

Answer: B — To meter the proper quantity of fuel for the amount of air entering the engine.

The metering system maintains an appropriate fuel-air relationship as airflow and operating conditions change.

Question 2

What happens to static air pressure as air velocity increases through the throat of a carburetor venturi?

A. It increases
B. It decreases
C. It remains constant

Answer: B — It decreases.

The low pressure at the venturi throat helps create the pressure differential that causes fuel to discharge into the airstream.

Question 3

What maintains the fuel level in the float chamber of a float-type carburetor?

A. An accelerating pump
B. A float-operated needle valve
C. An economizer valve

Answer: B — A float-operated needle valve.

As fuel level falls, the float drops and allows the inlet valve to admit more fuel.

Question 4

Why is a separate idle system required in a float carburetor?

A. Airflow through the main venturi is too low at idle to produce sufficient fuel discharge
B. Fuel pressure becomes excessive at idle
C. The main metering jet closes whenever the throttle closes

Answer: A — Airflow through the main venturi is too low at idle to produce sufficient fuel discharge.

The idle passage supplies fuel near the throttle valve when the main system cannot meter adequately.

Question 5

What is the purpose of the carburetor accelerating system?

A. To increase engine RPM automatically
B. To provide additional fuel during rapid throttle opening
C. To lean the mixture during acceleration

Answer: B — To provide additional fuel during rapid throttle opening.

It prevents a temporary excessively lean mixture as airflow increases faster than fuel flow.

Question 6

An engine hesitates when the throttle is opened rapidly but otherwise runs normally. Which carburetor system should receive particular attention?

A. Accelerating system
B. Idle cutoff system
C. Float vent system only

Answer: A — Accelerating system.

A defective accelerating pump or circuit can cause a temporary lean condition during rapid acceleration.

Question 7

What is the purpose of an economizer or power-enrichment system?

A. To supply additional fuel during high-power operation
B. To shut off fuel during deceleration
C. To maintain constant fuel pressure at idle

Answer: A — To supply additional fuel during high-power operation.

High-power operation commonly requires a richer mixture for power and cooling.

Question 8

An engine operates normally at cruise but develops a mixture-related problem at high power. Which carburetor circuit may be suspect?

A. Economizer or power-enrichment circuit
B. Idle circuit
C. Primer only

Answer: A — Economizer or power-enrichment circuit.

The economizer becomes particularly important at high-power settings.

Question 9

What does moving the mixture control to idle cutoff accomplish?

A. Increases airflow
B. Stops or greatly reduces metered fuel flow so the engine stops
C. Increases fuel pressure

Answer: B — Stops or greatly reduces metered fuel flow so the engine stops.

Idle cutoff is used to stop fuel delivery through the metering system.

Question 10

Why must a reciprocating engine normally be leaned as altitude increases?

A. Fuel becomes heavier with altitude
B. Air density decreases, which otherwise causes the mixture to become progressively richer
C. Fuel pressure always increases with altitude

Answer: B — Air density decreases, which otherwise causes the mixture to become progressively richer.

Less air mass enters the engine at altitude, so fuel must be reduced to maintain the desired fuel-air ratio.

Question 11

What two effects are major contributors to temperature reduction inside a float carburetor?

A. Compression and friction
B. Fuel vaporization and the pressure drop through the venturi
C. Exhaust scavenging and ram pressure

Answer: B — Fuel vaporization and the pressure drop through the venturi.

Both effects can substantially lower carburetor temperature.

Question 12

Where does carburetor ice commonly accumulate?

A. Only inside the float chamber
B. Around the venturi and throttle plate
C. Only at the fuel inlet screen

Answer: B — Around the venturi and throttle plate.

Ice in these areas restricts airflow and can progressively reduce power.

Question 13

Why does application of carburetor heat normally cause an initial loss of engine power?

A. Heated air is less dense
B. Heated air is more dense
C. Carburetor heat shuts off the main metering jet

Answer: A — Heated air is less dense.

Less-dense induction air contains less oxygen mass and normally reduces power.

Question 14

What is vapor lock?

A. Ice blocking the carburetor venturi
B. Fuel vapor forming in the fuel system and interfering with normal liquid fuel flow
C. A mechanically locked fuel selector valve

Answer: B — Fuel vapor forming in the fuel system and interfering with normal liquid fuel flow.

Vapor bubbles can disrupt pump operation and fuel delivery.

Question 15

Which conditions promote vapor lock?

A. Low fuel temperature and high pressure
B. High fuel temperature, low pressure, and excessive turbulence
C. High fuel pressure and low altitude only

Answer: B — High fuel temperature, low pressure, and excessive turbulence.

These conditions increase the likelihood of premature fuel vaporization.

Question 16

Why can increasing altitude increase susceptibility to vapor lock?

A. Atmospheric pressure decreases
B. Fuel density always doubles
C. Fuel temperature instantly decreases below freezing

Answer: A — Atmospheric pressure decreases.

Lower pressure makes fuel more likely to vaporize.

Question 17

What is a major difference between continuous-flow fuel injection and a float carburetor?

A. Fuel injection supplies metered fuel under pressure to individual cylinder nozzles
B. Fuel injection does not meter fuel
C. A fuel injection system requires a float bowl at each cylinder

Answer: A — Fuel injection supplies metered fuel under pressure to individual cylinder nozzles.

Continuous-flow systems meter pressurized fuel and distribute it to individual discharge nozzles.

Question 18

What is the purpose of a fuel-air control unit in a continuous-flow injection system?

A. To meter fuel in relation to engine airflow
B. To ignite the mixture
C. To cool the exhaust system

Answer: A — To meter fuel in relation to engine airflow.

It helps establish the correct relationship between airflow and fuel flow.

Question 19

What is the function of the fuel manifold valve or flow divider?

A. To distribute metered fuel to the individual cylinders
B. To return all fuel to the tank
C. To control ignition timing

Answer: A — To distribute metered fuel to the individual cylinders.

The flow divider routes metered fuel through individual lines to the injector nozzles.

Question 20

A partially clogged fuel injection nozzle will most directly affect what?

A. All cylinders equally
B. The mixture supplied to the affected cylinder
C. Magneto timing

Answer: B — The mixture supplied to the affected cylinder.

A restricted nozzle reduces fuel flow to its cylinder and can create a lean condition.

Question 21

An injected engine runs rough and one cylinder indicates a lean mixture. What fuel-system component should be considered?

A. The individual injector nozzle for that cylinder
B. The propeller governor
C. The exhaust stack on every cylinder

Answer: A — The individual injector nozzle for that cylinder.

A contaminated or restricted nozzle is a logical suspect when the problem is isolated to one cylinder.

Question 22

Which component normally provides fuel pressure to a continuous-flow fuel injection system during normal engine operation?

A. Engine-driven fuel pump
B. Magneto
C. Oil pressure relief valve

Answer: A — Engine-driven fuel pump.

The engine-driven pump supplies the pressure required by the metering and distribution system.

Question 23

What is one advantage of continuous-flow fuel injection compared with a conventional float carburetor?

A. More direct fuel distribution to individual cylinders
B. Elimination of all fuel-system maintenance
C. No requirement for fuel pressure

Answer: A — More direct fuel distribution to individual cylinders.

Individual-cylinder fuel distribution can improve mixture distribution.

Question 24

What should be inspected if a continuous-flow injection system has uneven fuel distribution?

A. Injector nozzles, individual fuel lines, and the flow divider
B. Only the spark plug leads
C. Only the oil filter

Answer: A — Injector nozzles, individual fuel lines, and the flow divider.

Restrictions or faults in the distribution system can create unequal cylinder fuel flow.

Question 25

What is the primary purpose of an engine-driven fuel pump?

A. Supply fuel to the metering system at the required pressure and flow
B. Measure exhaust gas temperature
C. Control propeller pitch

Answer: A — Supply fuel to the metering system at the required pressure and flow.

The metering device requires an adequate supply at the specified pressure and flow.

Question 26

What is a common purpose of an electric boost or auxiliary fuel pump?

A. Starting, backup pressure, or vapor suppression depending on the aircraft
B. Controlling ignition timing
C. Cooling the magnetos

Answer: A — Starting, backup pressure, or vapor suppression depending on the aircraft.

Exact use is aircraft-specific, but boost pumps commonly support these functions.

Question 27

Why can a partially clogged fuel filter cause power loss even if fuel is still reaching the engine?

A. The restriction may prevent the required fuel flow at higher engine demand
B. Fuel filters control ignition timing
C. Any fuel flow guarantees full power

Answer: A — The restriction may prevent the required fuel flow at higher engine demand.

A system may supply enough fuel for idle or cruise yet fail at high power.

Question 28

What should be examined when inspecting an engine fuel filter or strainer?

A. Evidence of contamination and restriction
B. Propeller blade angle
C. Magneto breaker point gap

Answer: A — Evidence of contamination and restriction.

Debris can restrict fuel flow and provide clues about contamination elsewhere in the system.

Question 29

Why are fuel drains located at low points in a fuel system?

A. Water and contaminants may collect there
B. Fuel pressure is always highest there
C. They increase octane rating

Answer: A — Water and contaminants may collect there.

Water is denser than aviation gasoline and tends to settle at low points.

Question 30

What is an important consideration when routing engine fuel lines?

A. Avoid excessive heat, chafing, sharp bends, and conditions that encourage vapor formation
B. Route every line against the exhaust for heating
C. Make all lines as short as possible regardless of interference

Answer: A — Avoid excessive heat, chafing, sharp bends, and conditions that encourage vapor formation.

Correct routing protects the line and helps maintain reliable fuel flow.

Question 31

What could a kinked or internally restricted fuel line cause?

A. Reduced fuel flow and possible power loss
B. Increased ignition voltage
C. Higher propeller RPM independent of engine power

Answer: A — Reduced fuel flow and possible power loss.

Restrictions become especially significant when fuel demand is high.

Question 32

What is the purpose of a fuel shutoff valve?

A. Permit fuel flow to be stopped when required
B. Automatically increase octane
C. Control carburetor air temperature

Answer: A — Permit fuel flow to be stopped when required.

Fuel valves provide controlled routing or isolation of fuel.

Question 33

During a fuel-system inspection, why should flexible hoses be checked carefully?

A. For deterioration, leaks, chafing, security, and proper routing
B. Only for paint color
C. Because hoses control spark timing

Answer: A — For deterioration, leaks, chafing, security, and proper routing.

Fuel hoses must remain leak-free and structurally sound in a demanding environment.

Question 34

What is the basic purpose of a turbine engine fuel control?

A. Schedule the correct fuel flow for engine operating conditions
B. Maintain constant aircraft altitude
C. Supply lubrication to turbine bearings

Answer: A — Schedule the correct fuel flow for engine operating conditions.

Turbine fuel controls meter fuel during start, acceleration, steady operation, and deceleration.

Question 35

Why can’t turbine-engine fuel flow simply be proportional to throttle position?

A. Safe fuel flow also depends on engine speed, airflow, pressure, temperature, and other operating conditions
B. Turbine engines do not have throttles
C. Fuel flow never changes after start

Answer: A — Safe fuel flow also depends on engine speed, airflow, pressure, temperature, and other operating conditions.

Fuel must be scheduled to match the engine’s ability to accept and burn it safely.

Question 36

What is a hydromechanical fuel control?

A. A fuel control using mechanical and hydraulic elements to schedule fuel
B. A spark ignition system
C. A turbine lubrication pump

Answer: A — A fuel control using mechanical and hydraulic elements to schedule fuel.

These controls use precision valves, springs, diaphragms, bellows, pressures, and related mechanisms.

Question 37

What does the term fuel scheduling mean in a turbine engine?

A. Determining the appropriate metered fuel flow for current engine conditions
B. Planning the aircraft’s next refueling stop
C. Measuring only the quantity remaining in the tanks

Answer: A — Determining the appropriate metered fuel flow for current engine conditions.

Fuel scheduling is controlled metering throughout the engine operating envelope.

Question 38

What is the function of a turbine engine fuel nozzle?

A. Atomize and introduce metered fuel into the combustion airflow
B. Compress incoming air
C. Drive the accessory gearbox

Answer: A — Atomize and introduce metered fuel into the combustion airflow.

Fine atomization promotes efficient mixing and stable combustion.

Question 39

Why is uniform fuel distribution among turbine fuel nozzles important?

A. It helps prevent uneven combustion temperatures and localized hot spots
B. It maintains tire pressure
C. It changes compressor blade angle

Answer: A — It helps prevent uneven combustion temperatures and localized hot spots.

Uneven fuel distribution can create damaging temperature patterns.

Question 40

What condition can result if excessive fuel is introduced during a turbine-engine start?

A. Hot start
B. Carburetor icing
C. Hydraulic lock in the landing gear

Answer: A — Hot start.

Too much fuel for the available airflow can cause excessive turbine temperature.

Question 41

What is a hung start?

A. The engine lights off but fails to accelerate normally to idle speed
B. The engine immediately accelerates beyond redline
C. Fuel freezes in the tank

Answer: A — The engine lights off but fails to accelerate normally to idle speed.

Possible causes include inadequate starter performance, fuel scheduling problems, or excessive drag.

Question 42

During a turbine start, ignition is present but there is no light-off. Which system should also be investigated?

A. Fuel supply, fuel control, and fuel nozzle system
B. Cabin lighting only
C. Propeller anti-ice only

Answer: A — Fuel supply, fuel control, and fuel nozzle system.

Combustion requires both ignition and an adequate, correctly delivered fuel supply.

Question 43

What does FADEC stand for?

A. Full Authority Digital Engine Control
B. Fuel Air Distribution Electrical Control
C. Flight Automatic Data Engine Computer

Answer: A — Full Authority Digital Engine Control.

FADEC electronically manages engine operation, including fuel scheduling.

Question 44

What is a major advantage of electronic engine control?

A. It can use multiple sensed engine parameters to calculate precise fuel requirements
B. It eliminates the need for engine sensors
C. It makes fuel metering unnecessary

Answer: A — It can use multiple sensed engine parameters to calculate precise fuel requirements.

Electronic controls continuously process engine data and command the metering system.

Question 45

In a FADEC-equipped engine, what generally determines the actual fuel-metering command?

A. Computer logic using pilot commands and engine sensor inputs
B. A carburetor float only
C. The fuel tank vent alone

Answer: A — Computer logic using pilot commands and engine sensor inputs.

The pilot requests power while the control system determines how to achieve it within programmed limits.

Question 46

When troubleshooting an electronically controlled fuel system, what should be considered in addition to mechanical fuel components?

A. Sensors, wiring, connectors, control units, and actuators
B. Only tire pressure
C. Only propeller paint condition

Answer: A — Sensors, wiring, connectors, control units, and actuators.

Electrical and data-related faults are part of modern fuel-system troubleshooting.

Question 47

An engine operates normally at idle and moderate power but loses power at maximum power. What should be checked?

A. Whether the fuel system can supply the required flow at high demand
B. Only the idle stop screw
C. Only the battery state of charge

Answer: A — Whether the fuel system can supply the required flow at high demand.

A restriction, weak pump, clogged filter, or high-power metering problem may appear only at high demand.

Question 48

An engine will not idle but operates at higher RPM. Which area deserves particular attention?

A. Idle metering circuit and idle mixture adjustment
B. Turbine fuel nozzle manifold
C. Propeller feathering accumulator

Answer: A — Idle metering circuit and idle mixture adjustment.

A fault limited to low-power operation points toward low-airflow fuel metering.

Question 49

Before adjusting a carburetor or fuel injection system, what information should a mechanic use?

A. Applicable manufacturer maintenance data and procedures
B. A generic adjustment found on another engine
C. Personal preference

Answer: A — Applicable manufacturer maintenance data and procedures.

The FAA handbook teaches theory; actual adjustments must follow the applicable technical data.

Question 50

What is the best overall troubleshooting sequence for an engine fuel-system problem?

A. Verify supply, pressure/flow, metering, and distribution systematically
B. Replace the carburetor immediately
C. Adjust every component until the engine runs

Answer: A — Verify supply, pressure/flow, metering, and distribution systematically.

A systematic approach helps isolate the actual fault and avoids unnecessary adjustments.

FAA ACS Areas Covered

The FAA Powerplant ACS identifies the following knowledge areas under Engine Fuel and Fuel Metering Systems:

• AM.III.I.K1 — Fuel/air ratio and fuel metering, and carburetor theory and operation
• AM.III.I.K2 — Float carburetor theory, components, operation, and adjustment
• AM.III.I.K3 — Pressure carburetor theory, operation, and adjustment
• AM.III.I.K4 — Continuous-flow fuel injection theory, components, operation, troubleshooting, and adjustment
• AM.III.I.K5 — Digital engine control module, such as FADEC
• AM.III.I.K6 — Hydromechanical fuel control system design and components
• AM.III.I.K7 — Fuel nozzles and manifolds
• AM.III.I.K8 — Turbine engine fuel metering systems
• AM.III.I.K9 — Engine fuel-system inspection requirements
• AM.III.I.K10 — Fuel-system operation
• AM.III.I.K11 — Fuel heaters
• AM.III.I.K12 — Fuel lines
• AM.III.I.K13 — Fuel pumps
• AM.III.I.K14 — Fuel valves
• AM.III.I.K15 — Fuel filters
• AM.III.I.K16 — Engine fuel drains

Important: These 50 questions are original study questions based on FAA subject matter. They should not be represented as leaked, current, or verbatim FAA knowledge-test questions.

61. Final Thoughts

Aircraft fuel systems demonstrate why understanding basic principles is so important in aircraft maintenance.

At first, the system may appear to be a collection of unrelated components:

• Pumps
• Carburetors
• Servos
• Floats
• Valves
• Filters
• Manifolds
• Nozzles
• Sensors
• Computers

But every component supports the same fundamental process.

The engine needs fuel.

That fuel must arrive:

• At the correct pressure
• At the correct flow rate
• In the correct quantity
• At the correct time
• At the correct location

For a reciprocating engine, fuel must be matched with the correct amount of air so that the cylinders can produce controlled combustion.

For a turbine engine, fuel must be carefully scheduled so that the combustion process remains stable while the engine accelerates, decelerates, changes altitude, and produces varying levels of thrust or shaft power.

Once you understand that, fuel-system troubleshooting becomes much more logical.

Instead of memorizing hundreds of isolated facts, ask:

Where is the fuel supposed to go, what controls its flow, and what should cause that flow to change?

That question can lead you through almost any aircraft fuel metering system.

FAA References

Primary Reference

Federal Aviation Administration
Aviation Maintenance Technician Handbook—Powerplant
FAA-H-8083-32B

Chapter 2: Engine Fuel & Fuel Metering Systems

FAA publication page:

https://www.faa.gov/regulationspolicies/handbooksmanuals/aviation/faa-h-8083-32b-aviation-maintenance-technician

Direct FAA Chapter 2 PDF:

https://www.faa.gov/sites/faa.gov/files/04_amtp_ch2.pdf

Chapter 2 includes FAA material covering topics such as:

• Fuel system requirements
• Aviation fuels
• Vapor lock
• Carburetor principles
• Float-type carburetors
• Carburetor fuel metering systems
• Pressure carburetors
• Reciprocating-engine fuel injection
• Fuel pumps
• Turbine-engine fuel systems
• Fuel controls
• Fuel nozzles
• Electronic engine controls

FAA Powerplant Airman Certification Standards

Federal Aviation Administration
Aviation Mechanic General, Airframe, and Powerplant Airman Certification Standards
FAA-S-ACS-1

The Powerplant ACS identifies Engine Fuel and Fuel Metering Systems as Subject I and defines the associated knowledge, risk-management, and skill elements.

https://www.faa.gov/training_testing/testing/acs

Additional FAA Resource

The FAA maintains its current aviation maintenance handbooks through its Aviation Handbooks & Manuals collection:

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation

When performing actual maintenance, always use the applicable manufacturer’s current maintenance instructions, approved technical data, Airworthiness Directives, and applicable regulations.

This article is intended for educational and study purposes. It is not a substitute for aircraft or engine manufacturer maintenance instructions, approved technical data, or applicable FAA regulations.