Aircraft Electrical Systems

Study Materials

AMT-SYS, FAA-H-8083-31, AC 43.13-1

Typical Oral Questions

  1. What two things must you take into consideration when selecting the wire size to use in an aircraft electrical system installation?

    The current carrying capability of the wire and the voltage drop caused by the current flowing through the wire.

  2. What is the maximum number of wires that should be connected to any single stud in a terminal strip?

    Four.

  3. How is a wire bundle protected from chafing where the bundle goes through a hole in a fuselage frame or bulkhead?

    The edges of the hole are covered with a flexible grommet, and the bundle is secured to the structure with a cushioned clamp.

  4. What kind of clamp is used to secure a wire bundle to the aircraft structure?

    A cushioned clamp.

  5. Why are solderless splices usually better than soldered splices in the wiring of an aircraft electrical system?

    Soldered joints are usually stiff, and vibration can harden the wire and cause it to break. Solderless splices are designed to keep the joint flexible so vibration cannot cause the wire to break.

  6. What size generator must be used in an aircraft electrical system if the connected electrical load is 30 amps, and there is no way of monitoring the generator output?

    When monitoring is not practical, the total continuously connected electrical load must be no more than 80 percent of the rated generator output. This would require a generator with a rating of 37.5 amps. Practically, a 40-amp generator would be installed.

  7. Why must a switch be derated if it is used in a circuit that supplies incandescent lamps?

    The high inrush current caused by the low resistance of the cold filaments requires that the switches be derated.

  8. On which wing is the red navigation light?

    On the left wing.

  9. What kind of fault can be found in a generator armature with a growler?

    Shorted coils.

  10. Does an aircraft engine electric starter use a series or a parallel motor?

    A series-wound motor.

  11. What is the main disadvantage of aluminum wire over copper wire for use in an aircraft electrical system?

    Aluminum wire is more brittle than copper. It is more subject to breakage when it is nicked or when it is subjected to vibration.

  12. What kind of rectifier is used in the small DC alternators installed in most light aircraft?

    Six silicon diodes arranged in a three-phase, full-wave rectifier.

  13. What kind of instrument would you use to measure very high resistance?

    A megohmmeter. Megger is the registered trade name of such an instrument.

  14. When is it important that aircraft electrical system wire bundles be enclosed in some type of conduit?

    Any time a wire bundle is routed in an area where it is subject to abrasion or rough handling, it should be enclosed in a conduit.

  15. What size aluminum wire would be proper to replace a piece of four-gage copper wire?

    Two-gage. When you substitute aluminum wire for copper wire, use a wire that is two gage numbers larger.

  16. What is the smallest size aluminum wire that is approved for use in aircraft electrical systems?

    Six-gage.

  17. What three things must be synchronized before an aircraft AC generator is placed on the same bus with another AC generator?

    The voltage, the frequency, and the phase rotation.

  18. How can the direction of rotation of the armature of a DC shunt-wound electric motor be reversed?

    By reversing the connections to the shunt field coil with reference to the armature.

  19. What is meant by flashing the field of a generator?

    Restoring the residual magnetism to the frame of the generator. This is done by passing battery current through the field coils in the direction it normally flows when the generator is operating.

Typical Practical Projects

  1. Using a wiring diagram of an aircraft electrical system, identify the switches, circuit breakers, wire splices, lamps, and motors.
  2. Given the current requirements and the length of the wire, select the smallest size wire that will carry the current without overheating or producing more than the allowable voltage drop.
  3. Install a solderless terminal on a piece of electrical wire.
  4. Given the specifications of an aircraft generator, find its rated current output.
  5. Check the diodes in a DC alternator for opens or shorts.
  6. Using an ohmmeter, determine whether or not the filament in a light bulb is good.
  7. Using a voltmeter, measure the output voltage of an aircraft generator.
  8. Explain to the examiner the correct way to flash the field of an aircraft generator.
  9. Using a voltmeter and an ohmmeter, demonstrate to the examiner the correct way to troubleshoot an aircraft electrical circuit.
  10. Inspect the ground cable of the battery installed in an aircraft for condition, tightness of connections, and for evidence of corrosion.
  11. Explain to the examiner the correct way to adjust the voltage controlled by a vibrator-type voltage regulator.
  12. Using a growler and continuity light, check the armature of an aircraft generator for shorted or open coils.
  13. Secure an electrical wire bundle to an aircraft structure using the proper clamps and grommets.
  14. Using the illustrated parts list for a particular aircraft, inspect an anticollision light installation to see whether or not it conforms with the aircraft man­ufacturer’s installation drawings.
  15. Using the correct test instruments, measure the current that flows through an electrical load specified by the examiner.
  16. Demonstrate to the examiner the correct way to tie an electrical wire bundle with spot ties.
  17. Given the specifications of a shock-mounted electrical component, describe to the examiner the correct choice of a bonding strap.
  18. Splice an electrical wire, using the correct type of splice and the correct insulation.
  19. Correctly attach wires to the terminals of a quick-disconnect connector.

[10-2024]