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Reading distributor electrode numbers on a radial

Aviation Mechanic Powerplant (AMP) practice question 4 of 11 on Ignition and Starting Systems. ACS element AM.III.H.K8 · 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 nine-cylinder radial engine fires in the order 1-3-5-7-9-2-4-6-8. The distributor electrode marked "3" serves which cylinder?

  1. AThe No. 3 cylinder, matching its number
  2. BThe No. 7 cylinder, fourth to be fired
  3. CThe No. 5 cylinder
Show the answer and explanation

Correct answer: C. The No. 5 cylinder

  • A — incorrect Distributor electrode numbers represent the sparking order, not engine cylinder numbers, so they do not match one for one.
  • B — incorrect Cylinder 7 is fourth in this firing order and is served by the electrode marked 4, not the one marked 3.
  • C — correct Distributor numbers give the magneto sparking order, so electrode 3 is the third cylinder fired, which in this firing order is cylinder 5.

BACKGROUND

The distributor consists of a revolving rotor and a stationary block whose terminals accept the ignition leads. On all four-stroke cycle engines the distributor rotates at one-half crankshaft speed, and the block carries as many electrodes as there are cylinders served by that magneto. The electrodes are numbered consecutively in the direction of rotor travel, and those numbers represent the magneto sparking order rather than engine cylinder numbers. Electrode 1 goes to cylinder No. 1, electrode 2 to the second cylinder fired, electrode 3 to the third cylinder fired, and so on.

STUDY TIP

Write the firing order out and count positions: the electrode number is a position in that list, never the cylinder number itself.

KEY POINTS

  • Distributor electrode numbers give the magneto sparking order.
  • Electrode 3 on a 1-3-5-7-9-2-4-6-8 engine serves cylinder 5.
  • The distributor turns at half crankshaft speed on four-stroke engines.

SOURCES

  • sources/amp-powerplant/ch04.txt "Secondary Electrical Circuit"
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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.