AMT Engine Fuel Metering Systems Questions and Answers

Question 1

In a reciprocating engine's continuous-flow fuel injection system, what is the primary function of the air bleed incorporated into the fuel discharge nozzle?

Accepted Answer

To assist in atomizing the fuel and improve vaporization at lower power settings.

Answer

To provide positive fuel cutoff during engine shutdown.

Answer

To filter the fuel just before it enters the intake port.

Answer

To meter the total quantity of fuel delivered to the cylinder.

Question 2

A technician is troubleshooting a float-type carburetor that provides an excessively rich mixture as the aircraft climbs in altitude, even with no pilot input. Which component is most likely malfunctioning?

Accepted Answer

The automatic mixture control (AMC).

Answer

The accelerator pump.

Answer

The main metering jet.

Answer

The throttle valve.

Question 3

Which of the following describes the fundamental operating principle of a pressure-type carburetor?

Accepted Answer

Fuel is delivered to a fuel metering unit under positive pressure, and the mixture ratio is controlled by the pressure of the metered fuel.

Answer

Fuel is drawn into the venturi by a pressure differential created between the float chamber and the venturi throat.

Answer

A sealed bellows expands and contracts with changes in air density to mechanically adjust a needle valve.

Answer

Fuel is sprayed directly into the combustion chamber on the compression stroke, timed by the engine's rotation.

Question 4

A pilot reports a gradual loss of RPM and engine roughness while flying on a warm, humid day at reduced power. Applying carburetor heat results in a further drop in RPM followed by a return to normal, smooth operation. What was the most likely cause of the initial problem?

Accepted Answer

Carburetor icing.

Answer

Vapor lock in the fuel lines.

Answer

Contamination in the main metering jet.

Answer

A malfunctioning accelerator pump.

Question 5

In a Full Authority Digital Engine Control (FADEC) system, what is the relationship between the Electronic Engine Controller (EEC) and the Fuel Metering Unit (FMU)?

Accepted Answer

The EEC is a computer that receives sensor inputs and sends precise electrical signals to the FMU, which then mechanically adjusts fuel flow.

Answer

The EEC is a hydromechanical backup that operates the FMU only if the primary system fails.

Answer

The FMU senses engine parameters and sends mechanical signals to the EEC, which then trims the fuel flow.

Answer

The FMU is the primary computer, and the EEC is a series of electronic sensors that provide data directly to the cockpit.

Question 6

What is a primary advantage of a fuel injection system over a float-type carburetor in a reciprocating engine?

Accepted Answer

Superior performance during aerobatic maneuvers and reduced risk of fuel vaporization icing.

Answer

Reduced susceptibility to impact icing on the air filter.

Answer

Simpler construction with fewer moving parts.

Answer

Inherent ability to operate with lower octane fuels.