Powerplant Oral

In what position should the crankshaft be when a magneto is being timed to the engine?

The piston in cylinder number 1 should be in the correct position for ignition to occur. This is normally about 30 degrees before top center on the compression stroke.

What is checked on engine runup to determine the operational condition of the engine?

Idling RPM and manifold pressure, engine acceleration, maximum static RPM and manifold pressure, magneto drop, ignition switch safety check, propeller pitch change, propeller feathering, oil pressure, fuel pressure, and fuel flow.

What are the two types of turbine compressors?

Centrifugal flow and axial flow.

Where are most APUs located in modern jet transport aircraft?

In the tailcone of the fuselage.

What is the function of an APU?

An APU provides electric power and compressed air when the main engines are not operating.

What are two sources of compressed air from an APU?

From bleed air from the APU turbine compressor, or from a load compressor driven by a free turbine in the engine.

Where in the maintenance information based on the ATA-100 system would you find instructions for inspecting and servicing the engine of an airborne APU?

In section 49-20.

How is most of the troubleshooting done for a modern APU?

By the fault codes generated by the FADEC.

What ensures that an APU will not be shut down while it is too hot?

The APU fuel control incorporates an automatic time-delay feature that closes the bleed air valve to remove most of the load and reduce the APU temperature before it is shut down.

What prevents the APU exceeding its safe operating limits when the bleed air valve is wide open?

The FADEC monitors the load and regulates the fuel going to the APU to prevent it from exceeding its safe limits.

What document would you use to find the safety procedures to follow when replacing an igniter plug in an APU engine?

The maintenance manual for the APU.

What adjustments and rigging are accomplished on a turbine engine?

The primary rigging on a turbine engine involves the adjustment of power control levers and cables, followed by careful adjustment of the fuel control unit to trim the engine for the correct idle speeds and to obtain maximum thrust.

What is an EICAS (engine indicating and crew alerting system)?

EICAS is an electronic instrumentation system that monitors airframe and engine parameters and displays the essential information on a video display on the instrument panel. Only vital information is continually displayed, but when any sensed parameters fall outside of their allowable range of operation, they are automatically displayed.

What would most likely cause a false fire alarm in a thermistor-type continuous-loop system?

A kinked or pinched continuous loop element.

If there is a break in a single-wire continuous-loop fire detector element, and the system tests bad, will it indicate the presence of a fire?

Yes, even though it tests bad, it will still indicate the presence of a fire.

What maintenance is allowed on a continuous-loop fire detection system?

Inspect and replace as needed the continuous-loop element, the controller, and the fire warning bell and/or light.

What is used as a fire extinguishing agent in some older aircraft?

Carbon dioxide (CO2)

What fire extinguishing agent is used in the high-rate discharge bottles installed in a jet transport aircraft?

Halon 1211 or 1301.

How is a high-rate discharge bottle of fire extinguishing agent discharged?

A powder charge is ignited and it blows a cutter through a frangible disc that seals the bottle.

What precaution must be taken when checking the electrical circuit for igniting the powder charge in the valve of a high-rate discharge bottle?

The current used to check the integrity of the electric circuit must not be high enough to ignite the powder charge.

What color and marking identifies the fluid lines that carry the fire extinguishing agent in an aircraft?

Brown tape with a series of diamonds on it.

What is used as a rectifier to produce direct current in a DC generator?

Brushes and a commutator.

What are two ways wires can be attached to the pins in a cannon plug?

a. By soldering the wires into pots on the pins and sockets.

b. By crimping tapered pins onto the wires and inserting the pins into tapered holes in the pins and sockets.

Why is stranded wire rather than solid wire used in most powerplant electrical systems?

Solid wire is likely to break when it is subjected to vibration.

What two things must be considered in selection of wire size when making an electrical installation in an aircraft?

The current-carrying capability of the wire, and the voltage drop caused by current flowing through the wire.

What is used to protect a wire bundle from chafing where it passes through a hole in a bulkhead or frame?

A grommet around the edges of the hole.

How are electrical wires protected where they pass through an area of high temperature?

Wires passing through these areas are insulated with high-temperature insulation, and the wires are enclosed in some type of protective conduit.

What is the minimum separation allowed between a wire bundle and a fluid line that carries combustible fluid or oxygen?

Six inches whenever possible. If not practical, the wires should not run parallel to fuel or oxygen lines and a minimum of two inches must be maintained.

Which aircraft electrical circuit does not normally contain a fuse or circuit breaker?

The starter motor circuit.

When should aircraft wiring be installed in a conduit?

When the wiring passes through an area in the aircraft where open wiring could likely be damaged, such as through a wheel well.

What is meant by a trip-free circuit breaker?

A circuit breaker that opens a circuit any time an excessive amount of current flows, regardless of the position of the circuit breaker’s operating handle.

Which way should the toggle of a switch that controls the propeller pitch move to place the propeller in low pitch (high RPM)?

Forward.

Why are protective covers placed over some switches in an aircraft electrical circuit?

To prevent the switch from being inadvertently actuated.

What is straight mineral oil?

It is the lubricating oil as obtained by fractional distillation of crude oil. It does not have any additives.

What is ashless dispersant (AD) oil?

A mineral lubricating oil containing additives that disperse the contaminants throughout the oil so they will not clump and clog oil passages. There are no ash-forming additives in AD oil.

What is synthetic oil?

A lubricating oil that is made by chemically changing the nature of an oil base to give it the needed characteristics. Synthetic oil is the primary oil for turbine engines.

Is automotive oil suitable for use in aircraft engines?

No, automotive and aviation oils are formulated for entirely different operating conditions.

What is meant by a multiviscosity oil?

It is a lubricating oil with a viscosity index improver that increases the viscosity of the oil when it is hot and decreases the viscosity when it is cold.

Where can you find the grade of engine oil specified for a particular aircraft?

In the airplane flight manual or the pilot’s operating handbook for the aircraft.

What are the six functions of the oil in an aircraft engine?

a. Reduces friction.

b. Seals and cushions.

c. Removes heat.

d. Cleans inside the engine.

e. Protects against corrosion.

f. Performs hydraulic action.

What is the purpose of an air-oil separator, or deaerator, in a turbine engine oil tank?

In normal operation, the oil picks up a quantity of air and it is swirled as it enters the deaerator. The swirling action releases the air from the oil, and the air is used to pressurize the oil tank.

How is oil pressure regulated in an aircraft engine?

A pressure-relief valve senses the desired pressure and sends excess oil back into the engine sump.

What is the purpose of the restricted orifice in the line between the oil pressure gauge and the engine?

The restricted fitting helps dampen any pulsations in the oil pressure caused by the pump.

What is a hot-tank lubrication system for a turbojet engine?

A lubrication system in which the oil cooler is in the pressure subsystem and the scavenged oil is not cooled before it is returned to the tank.

What is a cold-tank lubrication system for a turbojet engine?

A lubrication system in which the oil cooler is in the scavenge subsystem and the scavenged oil is cooled before it is returned to the tank.

Where does a dry sump oil system store oil?

In a reservoir outside the engine through the use of a scavenge pump and external tubing.

What is an all-weather spark plug?

A shielded spark plug that has a recess in the shielding in which a resilient grommet on the ignition lead forms a watertight seal.

What is meant by the reach of a spark plug?

The length of the threads on the spark plug that screw into the cylinder head.

What is the difference between a hot spark plug and a cold spark plug?

A hot spark plug has a long path for the heat to travel between the nose core insulator and the spark plug shell. In a cold spark plug, the heat has a shorter distance to travel, and the spark plug operates cooler than a hot spark plug.

What is the advantage of fine-wire spark plugs over massive electrode spark plugs.

Fine-wire spark plugs have a firing end that is more open than that of a massive electrode spark plug. The open firing end allows the gases that contain lead to be purged from the spark plug so they will not form solid lead contaminants.

Why is it important that the spark plugs be kept in numbered holes in a tray when they are removed from an engine?

Spark plugs tell a good deal about the internal condition of the cylinders from which they were taken. By knowing the cylinder from which each spark plug came, the mechanic can take the proper action when a spark plug indicates such conditions as detonation or overheating.

Why is it important that a torque wrench always be used when installing spark plugs in an aircraft engine?

If the spark plugs are not put in tight enough, there is a possibility of a poor seal; if they are put in too tight, there is danger of cracking the insulation or damaging the threads on the spark plug or the cylinder.

What kind of gauge should be used to measure the electrode gap in aircraft spark plugs?

A round wire gauge.

What is the function of the capacitor in a magneto?

The capacitor minimizes arcing at the breaker points, and it speeds up the collapse of the primary current as the breaker points open.

What happens in a magneto ignition system when the ignition switch is placed in the Off position?

The primary circuit is connected to ground.

What is checked when a magneto is internally timed?

Internally timing a magneto consists of adjusting the breaker points so they will open at the instant the rotating magnet is in its E-gap position, and the distribution rotor is in position to direct the high voltage to cylinder number one.

In what position should the ignition switch be placed when using a timing light on the magnetos?

In the Both position.

What is the E-gap position in magneto timing.

The E-gap angle is the position of the rotating magnet where the primary current flowing in the magneto coil is the greatest. The breaker points open when the rotating magnet is in its E-gap position.

What malfunction in the ignition system would cause an aircraft reciprocating engine to continue to run after the ignition switch is placed in the Off position?

The ignition switch is not grounding the magneto primary circuit.

What is the function of a float carburetor?

The float carburetor’s function is to measure airflow through the engine induction system and dispense the appropriate amount of gasoline into the airflow for all engine operating parameters and conditions. It must also provide the fuel in a state that is as vaporized as possible by the time ignition occurs in the engine cylinders.

What two things are adjusted when setting the idling conditions on a float carburetor?

a. Idling RPM by adjusting the throttle stop.

b. Idling mixture by adjusting idle needle valve.

What would likely cause a reciprocating engine equipped with a float carburetor to hesitate momentarily when the throttle is rapidly advanced from idle to full power?

A malfunctioning accelerator pump.

How does a pressure-type carburetor operate?

A pressure-type carburetor discharges fuel into the airstream at a pressure well above atmospheric. This results in better vaporization and permits the discharge of fuel into the airstream on the engine side of the throttle valve. With the discharge nozzle located at this point, the drop in temperature due to fuel vaporization takes place after the air has passed the throttle valve and at a point where engine heat tends to offset it. Thus, the danger of fuel vaporization icing is practically eliminated. The effects of rapid maneuvers and rough air on the pressure-type carburetors are negligible since its fuel chambers remain filled under all operating conditions.

Are the instruments installed in an aircraft suitable for use when trimming a turbine engine?

No, a special analyzer/trimmer such as a JetCal should be used.

Where are the fuel strainers normally located in an aircraft fuel system?

Fuel strainers are located in the tank outlet, the main strainer is located at the lowest point in the fuel system, and there are strainers in the carburetor or fuel injection system.

How can you tell when a fuel strainer for a turbine engine has been bypassed?

There is an indicator button that will pop out. This button is usually painted red for easy identification of a bypass condition.

What does the pilot do to change the RPM of an engine equipped with a constant-speed propeller when it is operating withing the constant-speed range?

The pilot moves the propeller pitch control. This changes the compression on the speeder spring inside the governor which moves the pilot valve. The pilot valve directs oil into or out of the propeller to change the pitch of the blades. The change in pitch changes the air load on the propeller which changes the RPM.

What is the difference between a controllable propeller and a constant-speed propeller?

Basically, it is the control system. A controllable-pitch propeller uses a manually operated oil valve to control the pitch, and a constant-speed propeller uses a governor to control the valve.

When making a magneto check on an engine equipped with a constant-speed propeller, should the propeller control be in the low-pitch or the high-pitch position?

It should be in the low-pitch, high RPM position.

What is meant by a slave engine with regard to propeller synchronization?

This is the engine in a multi-engine airplane whose RPMs follow those set on the master engine.

How are propellers on a twin-engine airplane synchronized?

The propeller governor of the master engine is set to the desired RPM. A signal from the master engine governor is sent to the control box which sends a signal to a stepping motor. This motor adjusts the propeller governor and fuel control of the slave engine causing it to maintain exactly the same RPM as the master engine.