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Lead count on a six-cylinder FADEC ignition harness

Aviation Mechanic Powerplant (AMP) practice question 2 of 11 on Ignition and Starting Systems. ACS element AM.III.H.K6 · difficulty: applied. Want to answer it in a timed quiz? Use the Aviation Mechanic Powerplant (AMP) practice mode.

Question bank updated 2026-09-22

QUESTIONA six-cylinder engine uses a FADEC ignition system. How many leads does its high-voltage harness carry?

  1. A6 leads, one for each engine cylinder
  2. B12 leads, one for each spark plug
  3. C3 leads, one for each control unit
Show the answer and explanation

Correct answer: B. 12 leads, one for each spark plug

  • A — incorrect One lead per cylinder would feed only one plug per cylinder; each cylinder has two plugs, each with its own lead.
  • B — correct With two spark plugs per cylinder on all these engines, a six-cylinder engine has 12 leads and 12 spark plugs.
  • C — incorrect A six-cylinder engine does use three electronic control units, but each unit carries four spark plug towers, not a single lead.

BACKGROUND

A FADEC is a solid-state digital electronic ignition and fuel injection system that controls timing, mixture, and spark as one integrated system, so engines equipped with it need neither magnetos nor a manual mixture control. Each electronic control unit (ECU) serves a pair of opposing cylinders: unit 1 covers cylinders 1 and 2, unit 2 covers cylinders 3 and 4, and unit 3 covers cylinders 5 and 6. The ignition system consists of the high-voltage coils on top of each ECU, the high-voltage harness, and the spark plugs, and there are two spark plugs per cylinder on all these engines. Two coil packs sit in the upper portion of each ECU, and each pack generates a high-voltage pulse for two spark plug towers, one positive and one negative in polarity.

STUDY TIP

Count plugs, not cylinders: multiply cylinders by two plugs to get both the plug count and the lead count, and remember three ECUs serve six cylinders.

KEY POINTS

  • Two spark plugs per cylinder means 12 plugs and 12 leads on a six-cylinder engine.
  • Each ECU controls two opposing cylinders, one control channel per cylinder.
  • FADEC engines need no magnetos and no manual mixture control.

SOURCES

  • sources/amp-powerplant/ch04.txt "PowerLink Ignition System"
  • sources/amp-powerplant/ch04.txt "Electronic Control Unit (ECU)"
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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.