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Where low-tension ignition voltage is stepped up

Aviation Mechanic Powerplant (AMP) practice question 11 of 11 on Ignition and Starting Systems. ACS element AM.III.H.K8 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONIn a low-tension ignition system, where is the low voltage produced by the magneto raised to ignition voltage?

  1. AIn the distributor block inside the magneto
  2. BIn the shielded lead at the ignition switch
  3. CIn a transformer coil near each spark plug
Show the answer and explanation

Correct answer: C. In a transformer coil near each spark plug

  • A — incorrect The low-tension system uses a brush-type distributor and no air gaps there; the voltage is still low when it leaves the magneto.
  • B — incorrect The ignition switch works on the primary circuit and grounds it when off; it plays no part in raising voltage.
  • C — correct Low voltage flows to the primary winding of a transformer coil located near the spark plug, where transformer action raises it and short high-tension leads carry it to the plug.

BACKGROUND

Low-tension systems were developed because high voltage carried through long leads tends to leak, especially at the reduced air pressures of high altitude flight in turbosupercharged aircraft. In the low-tension system, the magneto generates a low voltage that travels to the primary winding of a transformer coil mounted near the spark plug, where transformer action raises it and very short high-tension leads finish the trip. Because high voltage exists only in those short leads, and because the brush-type distributor removes internal air gaps, flashover in the distributor and harness is virtually eliminated. Electrical leakage, which is worse in radio-shielded installations because the grounded conduit lies close to the wires, is considerably reduced.

STUDY TIP

Fix the picture of a transformer coil sitting at the cylinder, with only a stub of high-tension lead beyond it, and you will answer most low-tension questions.

KEY POINTS

  • Low-tension magnetos send low voltage to a transformer coil at each plug.
  • Transformer action raises it, and short leads feed the spark plug.
  • Short high-voltage runs and a brush distributor nearly eliminate flashover.

SOURCES

  • sources/amp-powerplant/ch04.txt "High- & Low-Tension Magneto Systems"
Practice the Aviation Mechanic Powerplant (AMP) test →Timed 100-question exam, by ACS area, or review your misses. Free.
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-32B Aviation Maintenance Technician Handbook – Powerplant, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.