22 Ignition & Starting Systems Practice Questions & Answers

1. 1. A high-tension magneto system is divided into three distinct circuits. Which grouping correctly names all three?

   • A.The magnetic circuit, the primary circuit, and the E-gap circuit
   • B.The primary circuit, the secondary circuit, and the P-lead circuit
   • C.The magnetic circuit, the primary circuit, and the secondary circuit✓ Answer
   • D.The magnetic circuit, the secondary circuit, and the distributor circuit

   A high-tension magneto is analyzed as three circuits: the magnetic circuit (rotating magnet, pole shoes, soft-iron core), the primary circuit (primary winding, breaker points, capacitor), and the secondary circuit (secondary winding, distributor, leads, spark plugs). The E-gap is a rotor position, not a circuit, and the P-lead is simply the grounding branch of the primary circuit.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, magneto operating principles (magnetic, primary and secondary circuits)Report a problem with this question

2. 2. In a high-tension magneto, the E-gap position is best described as:

   • A.a few degrees before neutral, where the magnetic flux in the core begins to reverse
   • B.the neutral position, where the magnet poles are aligned with the pole shoes
   • C.the position of maximum flux, where the breaker points have just finished closing
   • D.a few degrees past neutral, where the rate of flux change and primary current peak✓ Answer

   E-gap, or efficiency gap, is a few degrees of rotation past the neutral position in the normal direction of rotation. At that point the flux is changing most rapidly and primary current is at its maximum, so the breaker points are set to open there and the collapsing primary field induces the highest possible secondary voltage.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, magneto E-gap and breaker point openingReport a problem with this question

3. 3. During inspection of a magneto the breaker points are found badly burned and pitted, and the engine has a weak spark. Which condition most directly accounts for this?

   • A.A cracked distributor block, letting high tension flash over to a grounded surface
   • B.A weakened rotating magnet, reducing the flux available to the magnetic circuit
   • C.An open P-lead, leaving the primary circuit ungrounded at the ignition switch
   • D.A defective capacitor, allowing an arc across the points as the primary field collapses✓ Answer

   The capacitor is connected across the breaker points. It absorbs the surge of self-induced current the instant the points open, which prevents the arc that would burn the contact faces, and it speeds the collapse of the primary magnetic field so the secondary voltage rises. An open or leaky capacitor therefore shows up as burned, pitted points together with a weak spark.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, magneto capacitor function and breaker point conditionReport a problem with this question

4. 4. Why must a propeller be treated as capable of firing the engine even with the ignition switch OFF and the battery master switch off?

   • A.A magneto makes its own current and is switched off by grounding its primary circuit✓ Answer
   • B.A magneto is powered from the battery bus, which stays live through the starter relay
   • C.A magneto stores a charge in its capacitor that can reach the spark plugs when the shaft turns
   • D.A magneto discharges its secondary through the safety gap whenever the rotor is moved

   An aircraft magneto is a self-contained generator, so the ignition switch does not interrupt a supply of power; it grounds the magneto primary through the P-lead. If that lead is broken, its terminal is loose, or the switch is faulty, the primary is never grounded and the magneto will fire whenever the engine is turned, whatever position the switches are in.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, ignition switch and P-lead operation; hot magneto hazardReport a problem with this question

5. 5. At run-up rpm the ignition switch is moved from BOTH to LEFT and the rpm does not drop at all. The most probable cause is:

   • A.excessively wide plug gaps on the right magneto's plugs, weakening that magneto's spark
   • B.a worn cam follower in the left magneto, so its breaker points open later than set
   • C.a cracked distributor block in the left magneto, allowing high tension to flash over
   • D.an open ground lead on the right magneto, so it keeps firing in every switch position✓ Answer

   Selecting LEFT grounds the right magneto through its P-lead, so the engine should show a small rpm drop. No change at all means the right magneto was never grounded and is still firing, which points to an open ground lead or a defective switch. That same fault leaves the magneto hot, so it must be corrected before further operation.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, magneto check and ignition system troubleshootingReport a problem with this question

6. 6. Aircraft ignition leads are enclosed in a metal braid or conduit primarily to:

   • A.carry combustion heat away from the leads so the insulation does not break down
   • B.hold the leads at a fixed radius so vibration cannot chafe the insulation through completely
   • C.carry the radiated electromagnetic field to ground so it cannot interfere with radios✓ Answer
   • D.keep the high tension from leaking to ground where the leads pass near the exhaust

   The rapidly changing high-voltage current in an ignition lead radiates electromagnetic energy that would interfere with radio and navigation equipment. The metal shielding intercepts that field and conducts it to ground, and it also gives the lead mechanical protection. The shielding is not the conductor's insulation, and it does not stop internal leakage caused by a damaged lead.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, ignition harness construction and shieldingReport a problem with this question

7. 7. Internal timing of a magneto differs from timing the magneto to the engine in that internal timing:

   • A.sets point opening to the magnet's E-gap position, independent of the crankshaft✓ Answer
   • B.sets point opening to a crankshaft position, independent of the magnet's position
   • C.sets the distributor rotor to the firing order, and does not affect point opening
   • D.sets the breaker point clearance only, and does not affect when the points open

   Internal timing relates the opening of the breaker points to the position of the rotating magnet at E-gap and to the distributor rotor, and it is normally done with the magneto off the engine. Timing to the engine comes afterward and positions the complete magneto so that those internal events occur when the number one piston is the specified number of degrees before top center on the compression stroke.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, internal timing versus timing the magneto to the engineReport a problem with this question

8. 8. A magneto that was correctly timed internally at overhaul is found out of internal timing after a period of service. The usual cause is:

   • A.wear of the magneto drive gear in the accessory case
   • B.loss of magnetism in the rotating magnet over many hours
   • C.wear of the cam follower and the breaker point contact faces✓ Answer
   • D.hardening of the capacitor dielectric from operating heat

   Internal timing depends on exactly where in the magnet's rotation the breaker points begin to open, and that instant is set by the cam follower riding the breaker cam. As the follower and the contact faces wear, the points start opening later and internal timing drifts. A weakened magnet reduces spark energy but does not move the opening point.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, causes of internal timing change in serviceReport a problem with this question

9. 9. Ignition timing that is advanced beyond the specified setting most likely produces:

   • A.low power and high exhaust gas temperature, with burning late in the cycle
   • B.afterfiring in the exhaust, with unburned charge leaving the cylinder
   • C.detonation and preignition, with excessive pressure early in the power stroke✓ Answer
   • D.hard starting, with a magneto coming-in speed too high for cranking rpm

   An early spark lets the charge burn while the piston is still rising, so peak pressure and temperature occur too soon and oppose the piston's travel. Cylinder pressure and head temperature climb and detonation or preignition becomes likely. Retarded timing gives the opposite complaint: low power and high exhaust gas temperature because combustion continues into the exhaust stroke.

   Source: FAA Aviation Maintenance Technician Handbook — Powerplant, effects of advanced and retarded ignition timingReport a problem with this question

10. 10. A sharp clicking is heard from one magneto while the engine is being cranked, and it stops as the engine starts. The device producing it:

    • A.shifts the distributor rotor backward to fire a plug later in the stroke
    • B.winds a spring and then spins the magnet rapidly, giving a hot, retarded spark✓ Answer
    • C.closes an extra set of retard points through the starter solenoid circuit
    • D.feeds interrupted battery current to the primary, giving a stream of sparks

    The clicking identifies an impulse coupling. Its flyweights catch and hold the rotating magnet while the drive winds a spring, then release it so the magnet spins fast enough for a hot spark and late enough to avoid kickback. The device is purely mechanical and needs no electrical power; above a set cranking speed the flyweights fly outward and the coupling stops acting.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, impulse coupling operationReport a problem with this question

11. 11. Which statement correctly describes a shower of sparks starting system?

    • A.A separate starting coil fires each spark plug directly and bypasses the magneto secondary
    • B.A spring and flyweight coupling spins the magnet while retard points fire the plug late
    • C.A vibrator interrupts battery current to the magneto primary while retard breaker points fire late✓ Answer
    • D.A booster coil sends high tension straight to the distributor while the main points stay open

    In a shower of sparks system the magneto itself is conventional except for an added set of retard breaker points. A starting vibrator chops battery current and feeds it into the magneto primary, so the secondary delivers a continuous stream of sparks while the retard points hold ignition back from the normal advanced setting. Unlike an impulse coupling, the system depends on electrical power and is cut out when the switch leaves the start position.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, high-tension retard breaker vibrator (shower of sparks) systemReport a problem with this question

12. 12. An engine with a high compression ratio requires which kind of spark plug, and for what reason?

    • A.A hot plug, because a long insulator nose burns deposits off the firing end faster
    • B.A hot plug, because a longer thread reach places the electrodes deeper in the charge
    • C.A cold plug, because a wider electrode gap resists fouling at high cylinder pressure
    • D.A cold plug, because its short insulator nose moves heat quickly into the cylinder head✓ Answer

    Heat range is set mainly by the length of the insulator nose, which fixes the path heat must travel from the firing end to the cylinder head. A high-compression engine runs hotter, so it needs a cold plug with a short nose and rapid heat transfer; otherwise the electrodes can glow and ignite the charge before the spark occurs, which is preignition. A plug that runs too cold fouls instead.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, spark plug heat range and insulator nose lengthReport a problem with this question

13. 13. Electrode erosion has widened the gap of a used spark plug. What follows, and how is the gap measured?

    • A.The voltage needed to fire rises, and the gap is checked with a round wire gauge✓ Answer
    • B.The voltage needed to fire drops, and the gap is checked with a round wire gauge
    • C.The voltage needed to fire drops, and the gap is checked with a flat feeler gauge
    • D.The voltage needed to fire rises, and the gap is checked with a flat feeler gauge

    A wider gap needs a higher voltage to jump, which raises the magneto's coming-in speed, makes starting harder, and encourages the high tension to find an easier path elsewhere in the secondary. Because the ground electrodes of a massive-electrode plug are contoured rather than flat, a flat feeler gauge reads incorrectly; a round wire gauge inserted parallel to the center electrode is the correct tool.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, spark plug gap erosion and use of a round wire gaugeReport a problem with this question

14. 14. Which spark plug fouling condition results from a maintenance error rather than from engine operation?

    • A.Carbon deposits building up from a rich mixture and prolonged idling
    • B.Oil bridging the electrodes because of worn rings or valve guides
    • C.Graphite bridging the electrodes after careless antiseize application✓ Answer
    • D.Lead deposits forming during cruise at low cylinder head temperature

    Graphite-based antiseize compound is an excellent electrical conductor. Applied too heavily, or to the wrong threads, it can be carried onto the firing end and short the plug to ground. Compound goes on a few threads measured from the electrode end, never on the first thread and never on the electrodes. The other three conditions arise from how the engine is operated or from its mechanical condition.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, spark plug fouling and antiseize compound applicationReport a problem with this question

15. 15. Turbine engine igniter plugs last far longer than reciprocating engine spark plugs mainly because they:

    • A.are washed continuously by cooling air bled from the compressor case
    • B.fire at a much lower voltage than a magneto delivers to a spark plug
    • C.sit outside the burner rather than in the direct path of the combustion gases
    • D.operate at start and in selected flight phases rather than continuously✓ Answer

    Once a turbine engine lights off, combustion is continuous and self-sustaining, so the igniters are required only for starting and for continuous-ignition duty in conditions such as icing, heavy rain, or takeoff. Because they are de-energized for most of the flight, their service life is long in spite of the very high energy each discharge carries.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, turbine engine ignition system operation and igniter service lifeReport a problem with this question

16. 16. Turbine engines use capacitor discharge ignition systems mainly because such a system delivers:

    • A.high voltage with high heat intensity, able to arc a wide igniter gap✓ Answer
    • B.steady alternating voltage, able to hold a continuous arc across the gap
    • C.high voltage with low current, able to protect the exciter from overload
    • D.low voltage with long spark duration, able to keep a flame front moving

    Starting a turbine means lighting cold, poorly atomized fuel across a wide igniter gap, sometimes at altitude. A capacitor discharge system stores energy and releases it in a very short, very intense pulse, supplying both the voltage needed to ionize the wide gap and the heat intensity needed to ignite the mixture, which an ordinary induction system cannot do.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, capacitor discharge turbine ignition systemsReport a problem with this question

17. 17. Before disconnecting a high-tension lead from a turbine engine igniter plug, the mechanic must first:

    • A.open the aircraft battery switch and pull the ignition circuit breaker at the panel
    • B.remove the igniter plug from the liner so any discharge occurs outside the case
    • C.energize the system briefly so the exciter dumps its charge through the igniter gap
    • D.disconnect the low-voltage input at the exciter and let the stored energy bleed off✓ Answer

    A turbine exciter stores enough energy to injure or kill, and that energy remains stored after the system is switched off. The required practice is to disconnect the low-voltage primary lead at the exciter, wait the interval given in the maintenance data for the capacitor to bleed down, and then ground the high-tension lead before handling it. Opening the aircraft battery switch does not drain the capacitor.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, turbine ignition system maintenance safety precautionsReport a problem with this question

18. 18. During a turbine engine start, light-off occurs and exhaust gas temperature stays within limits, but the engine stabilizes at a low rpm and will not accelerate to idle. This is:

    • A.a hung start, usually traced to low starter power or a weak battery✓ Answer
    • B.a normal start, usually completed once the starter drops out on schedule
    • C.a wet start, usually traced to fuel entering the burner with no ignition
    • D.a hot start, usually traced to too much fuel for the airflow the engine has

    A hung start is one in which the engine lights but stabilizes below idle and will not accelerate. The engine is not receiving enough rotational energy from the starter, typically because starting air pressure or battery voltage is low, so compressor airflow never reaches self-sustaining speed. The correct response is to shut down and correct the starting power source rather than keep the engine at that speed.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, turbine engine starting sequence and start malfunctionsReport a problem with this question

19. 19. A direct-cranking electric starter for a reciprocating engine uses a series-wound direct current motor because that motor:

    • A.can be operated safely with no load applied to its output shaft
    • B.develops high torque at the low speeds where cranking starts✓ Answer
    • C.holds a nearly constant speed regardless of how the load changes
    • D.reverses its direction whenever the applied polarity is reversed

    In a series motor the field windings carry the full armature current, so field strength rises with load and torque is greatest when the motor is stalled or turning slowly. That is exactly what a cold engine demands at the start of cranking. The same characteristic means speed varies inversely with load, and a series motor must never be run unloaded because it can overspeed.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, reciprocating engine direct cranking electric startersReport a problem with this question

20. 20. In a starter-generator, what happens during the starting phase?

    • A.The shunt field carries the load current and holds cranking speed constant
    • B.The compensating field alone excites the machine and limits the inrush current
    • C.The series field carries the load current and produces strong cranking torque✓ Answer
    • D.The shunt and series fields oppose each other to keep peak current low

    A starter-generator is essentially a shunt generator with a heavy series winding added. During start the series field, together with the compensating and commutating windings, is connected in series with the power source, so the very large starting current creates a strong field and high cranking torque. After the start the unit is reconnected to run as a shunt generator, and it remains permanently engaged with the accessory drive.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, turbine engine starter-generator construction and operationReport a problem with this question

21. 21. How is internal mechanical damage in an air turbine starter normally detected?

    • A.By measuring bleed air pressure at the starter inlet during motoring
    • B.By reading the exhaust gas temperature rise during the motoring run
    • C.By checking the engine oil filter screen for ferrous particles after a start
    • D.By checking the magnetic drain plug in its oil sump for ferrous particles✓ Answer

    An air turbine starter carries its own oil supply in a self-contained sump, and that oil does not circulate through the engine, so engine oil analysis and the engine filter reveal nothing about the starter. The sump drain plug is magnetic, and ferrous particles clinging to it are the standard indication of gear or bearing distress inside the starter.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, air turbine starter oil system and magnetic drain plug inspectionReport a problem with this question

22. 22. On a reciprocating engine equipped with full authority digital engine control, ignition timing is:

    • A.set by the control unit from crankshaft speed, position, and manifold conditions✓ Answer
    • B.set by rotating the magneto in its slotted mounting flange when it is installed
    • C.varied by the pilot through the mixture control whenever the power setting changes
    • D.fixed at one advance value chosen to suit the engine's cruise power setting

    A full authority digital engine control system continuously monitors crankshaft speed and top center position, induction manifold pressure, and induction air temperature, and its electronic control unit sets both fuel delivery and ignition timing for each operating condition. Because the control unit performs those functions, the engine needs neither magnetos nor a manual mixture control, and there are no breaker points whose wear could shift the timing.

    Source: FAA Aviation Maintenance Technician Handbook — Powerplant, full authority digital engine control ignition and fuel controlReport a problem with this question

Practice questions based on the Aviation Mechanic Airman Certification Standards (FAA-S-ACS-1), 14 CFR parts 43, 65, and 91, and the FAA Aviation Maintenance Technician Handbook—Powerplant (FAA-H-8083-32). This site is not affiliated with or endorsed by the Federal Aviation Administration. This bank covers the POWERPLANT written test only; the General and Airframe written tests and the oral and practical tests are separate. Torque values, running clearances, compression limits, magneto timing angles, spark plug gaps, temperature and pressure limits, servicing quantities, and overhaul intervals always come from the manufacturer's current maintenance data, the type certificate data sheet, and the applicable airworthiness directives — never from a practice test. Confirm current eligibility and testing requirements with the FAA before you test. About the A&P mechanic certificate →