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Starter-generator field during start

Aviation Mechanic Airframe (AMA) practice question 2 of 24 on Aircraft Electrical Systems. ACS element AM.II.K.K2 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONDuring the engine start function, which field does the generator control unit energize in a starter-generator?

  1. AThe series field, so the unit acts as a motor
  2. BThe parallel (shunt) field, so the unit acts as a motor
  3. CBoth fields at once, to increase starting torque
Show the answer and explanation

Correct answer: A. The series field, so the unit acts as a motor

  • A — correct During the start function the GCU energizes the series field and the armature, and the unit acts like a motor.
  • B — incorrect The parallel field is energized in the generating mode, after the series field is disconnected.
  • C — incorrect The two fields are used one at a time; the GCU disconnects the series field before energizing the parallel field.

BACKGROUND

High-output generators on turbine-powered corporate aircraft and turboprops often combine the starter and the generator in one housing, saving space and weight. A starter-generator contains two sets of field windings: one used to start the engine and one used to generate electrical power. During the start function the generator control unit energizes the series field and the armature so the unit behaves as a motor. During the generating mode the GCU disconnects the series field, energizes the parallel field, and controls the current produced by the armature. Because the unit performs two jobs, its control system is relatively complex.

STUDY TIP

Remember the pairing series field equals motoring and parallel field equals generating, and that the GCU switches between them rather than using both together.

KEY POINTS

  • A starter-generator has separate series and parallel field windings.
  • The series field is energized to motor the engine during start.
  • The parallel field is energized once the unit switches to generating.

SOURCES

  • sources/ama-airframe/ch09.txt "Generator Controls for High-Output Generators"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.