(ASA) Powerplant Oral Study Guide with
Questions & Answers
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
cylinder from which they were taken. By knowing the cylinder from which each spark plugs
came, the mechanic can take the proper action when a spark plug indicates such conditions as
detonation or overheating
What is the purpose of staggered timing between the two magnetos on an aircraft engine?
✔️✔️Engines in which the exhaust gas scavenging from the cylinders is uneven use staggered
ignition timing. The spark plug nearest the exhaust valve, where the fuel-air moisture is diluted,
fires before the spark plug on the intake side. By using staggered timing, the flame front caused
by the two spark plugs will meet in the center of the piston
In what position should the ignition switch be placed when using a timing light on the magnetos
✔️✔️In the both position
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 the possibility of a
poor seal, and they are put in too tight, there is a danger of cracking the insulation
,Why are pressurized magnetos used on most reciprocating-engine-powered aircraft that fly at
high altitudes? ✔️✔️Pressurized air is a better insulator that less dense air. By pressurizing the
distributors, the high voltage is kept from arcing across to the wrong electrode and causing
vibration and loss of engine power
What type of ignition system is used on most turbine engine? ✔️✔️High-intensity,
intermittent-duty, capacitor discharge ignition system
What is meant by the E-gap in magneto timing? ✔️✔️The E-gap angle is the position of the
rotating magnet when 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 is the function of an impulse coupling? ✔️✔️An impulse coupling is a spring-driven
coupling between the magnet and the engine. When the engine is being started, the impulse
coupling holds the rotating magnet until the piston passes over its top center position and starts
down. The impulse coupling releases the magnet and the spring spins it fast so that it produces a
hot and late spark
What kind of gage should be used to measure the electrode gap in aircraft spark plugs? ✔️✔️A
round wire gage
How many igniters are used in most turbine engines? ✔️✔️Two
,What are two types of ignition systems used in turbine engines? ✔️✔️High-voltage systems
and low-voltage system
With which type of ignition system is a glow plug igniter used? ✔️✔️A low-voltage system
How is the strength of the magnet in a magneto checked? ✔️✔️The magneto is put on a test
stand and rotated at a specified speed. The breaker points are held open and the primary current
is measured. The strength of the magnet determines the amount of primary current
In what position is the magnet in a magneto when the greatest change in flux density in the coil
core takes place? ✔️✔️It is a few degrees beyond its neutral position. When it is in this
position, the breaker points open and the primary current is interrupted. The flux change in the
coil core is the greatest
In what position is the magnet in a magneto when the breaker points begin to open? ✔️✔️In its
E-gap position, just a few degrees beyond its neutral 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 turns on the auto ignition system in a turbo-prop engine? ✔️✔️A torque pressure switch
energizes the system when the engine stops producing torque
Where does the fuel metering system of a turbine engine discharge its fuel? ✔️✔️The fuel is
discharged through spray nozzles into combustion chambers
What is adjusted when the fuel control unit of a turbine engine is trimmed? ✔️✔️The idle
speed and the maximum-thrust speed
What are two location water may be injected into a turbine engine? ✔️✔️At the compressor
inlet and at the inlet to the diffuser section
What is meant by a duplex nozzle in a turbine engine fuel metering system? ✔️✔️A duplex
fuel nozzle is on that has two fuel discharge passages. A flow divider sends fuel for low pressure
operation through one discharge passage, and when the engine demands more fuel, it is sprayed
out through the seconds discharge passage. The spray pattern keeps the flame centered in the
burner for all operating conditions
What is the function of a float carburetor? ✔️✔️The float carburetors function is to measure
airflow through the engine induction system and dispense the appropriate amount of a gasoline
into the airflow for all engine operating perimeters and conditions. It must also provide the fuel
in a state that is as vaporized as possible by the time the ignition occurs in the engine cylinders
Questions & Answers
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
cylinder from which they were taken. By knowing the cylinder from which each spark plugs
came, the mechanic can take the proper action when a spark plug indicates such conditions as
detonation or overheating
What is the purpose of staggered timing between the two magnetos on an aircraft engine?
✔️✔️Engines in which the exhaust gas scavenging from the cylinders is uneven use staggered
ignition timing. The spark plug nearest the exhaust valve, where the fuel-air moisture is diluted,
fires before the spark plug on the intake side. By using staggered timing, the flame front caused
by the two spark plugs will meet in the center of the piston
In what position should the ignition switch be placed when using a timing light on the magnetos
✔️✔️In the both position
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 the possibility of a
poor seal, and they are put in too tight, there is a danger of cracking the insulation
,Why are pressurized magnetos used on most reciprocating-engine-powered aircraft that fly at
high altitudes? ✔️✔️Pressurized air is a better insulator that less dense air. By pressurizing the
distributors, the high voltage is kept from arcing across to the wrong electrode and causing
vibration and loss of engine power
What type of ignition system is used on most turbine engine? ✔️✔️High-intensity,
intermittent-duty, capacitor discharge ignition system
What is meant by the E-gap in magneto timing? ✔️✔️The E-gap angle is the position of the
rotating magnet when 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 is the function of an impulse coupling? ✔️✔️An impulse coupling is a spring-driven
coupling between the magnet and the engine. When the engine is being started, the impulse
coupling holds the rotating magnet until the piston passes over its top center position and starts
down. The impulse coupling releases the magnet and the spring spins it fast so that it produces a
hot and late spark
What kind of gage should be used to measure the electrode gap in aircraft spark plugs? ✔️✔️A
round wire gage
How many igniters are used in most turbine engines? ✔️✔️Two
,What are two types of ignition systems used in turbine engines? ✔️✔️High-voltage systems
and low-voltage system
With which type of ignition system is a glow plug igniter used? ✔️✔️A low-voltage system
How is the strength of the magnet in a magneto checked? ✔️✔️The magneto is put on a test
stand and rotated at a specified speed. The breaker points are held open and the primary current
is measured. The strength of the magnet determines the amount of primary current
In what position is the magnet in a magneto when the greatest change in flux density in the coil
core takes place? ✔️✔️It is a few degrees beyond its neutral position. When it is in this
position, the breaker points open and the primary current is interrupted. The flux change in the
coil core is the greatest
In what position is the magnet in a magneto when the breaker points begin to open? ✔️✔️In its
E-gap position, just a few degrees beyond its neutral 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 turns on the auto ignition system in a turbo-prop engine? ✔️✔️A torque pressure switch
energizes the system when the engine stops producing torque
Where does the fuel metering system of a turbine engine discharge its fuel? ✔️✔️The fuel is
discharged through spray nozzles into combustion chambers
What is adjusted when the fuel control unit of a turbine engine is trimmed? ✔️✔️The idle
speed and the maximum-thrust speed
What are two location water may be injected into a turbine engine? ✔️✔️At the compressor
inlet and at the inlet to the diffuser section
What is meant by a duplex nozzle in a turbine engine fuel metering system? ✔️✔️A duplex
fuel nozzle is on that has two fuel discharge passages. A flow divider sends fuel for low pressure
operation through one discharge passage, and when the engine demands more fuel, it is sprayed
out through the seconds discharge passage. The spray pattern keeps the flame centered in the
burner for all operating conditions
What is the function of a float carburetor? ✔️✔️The float carburetors function is to measure
airflow through the engine induction system and dispense the appropriate amount of a gasoline
into the airflow for all engine operating perimeters and conditions. It must also provide the fuel
in a state that is as vaporized as possible by the time the ignition occurs in the engine cylinders
