Systems: Electrical

Quick refresher

The alternator normally supplies electricity while the engine runs and recharges the battery. The battery starts the engine and can supply limited backup power. A bus distributes electricity, and breakers protect the wiring.

General Knowledge Questions

1. What type of electrical system does this aircraft use?

   Most light trainers use direct current (DC). Check the POH for your airplane’s bus arrangement.

   • (E.g., direct current [DC] or alternating current [AC]; single- or dual-bus systems.)
2. What is the voltage and amperage of the system?

   Common examples are 14- or 28-volt charging systems with a 60-amp alternator. Use the ratings listed for your airplane.

   • (E.g., 14V/28V system, 60-amp alternator.)
3. What is the purpose of the alternator/generator?

   It normally supplies electricity while the engine runs and recharges the battery. The battery provides starting power and limited backup power.

   • How does it differ from the battery’s role?
4. What is a bus bar, and what is its purpose in the electrical system?

   A bus is a distribution point that sends electrical power to several circuits.

5. How does the aircraft handle an overvoltage situation?

   Overvoltage protection disconnects the alternator to protect the electrical equipment. Follow the airplane’s checklist.

6. What is the purpose of circuit breakers and fuses?

   They protect wiring by interrupting excessive current.

7. What happens if the alternator fails in flight?

   The battery can supply power for a limited time. Recognize the warning, reduce electrical demand and follow the checklist.

   • How will you recognize this, and what actions will you take?
8. How does the battery recharge during flight?

   The alternator or generator supplies charging current while it is operating normally.

9. What is the function of the voltage regulator?

   It keeps the charging-system voltage within its intended range.

System-Specific Questions

1. Explain the function of the master switch.

   It controls the main electrical supply. A split master usually has separate battery and alternator controls.

   • What does the split switch control (e.g., alternator and battery)?
2. What happens if the alternator or generator belt fails?

   A belt-driven unit stops producing power, leaving the battery to supply the load.

3. Which instruments or systems are electrically powered?

   Typical examples include radios, lights, avionics and, on some airplanes, fuel pumps, flaps and trim.

   • (E.g., lights, radios, fuel pump, flaps, avionics, etc.)
4. Does this aircraft have a standby alternator or battery? If so, how is it used?

   Check the POH and installed-equipment supplements. Know how to select the backup and what it can power.

5. How can you determine if the alternator/generator is functioning properly?

   Check the charging indications and warning lights described in the POH.

6. What systems or equipment would lose power first in an electrical failure?

   That depends on the airplane’s buses and backup supplies. Know which equipment is on the essential bus.

7. What is the role of the ammeter/voltmeter?

   An ammeter shows current; a voltmeter shows voltage. Abnormal readings can warn of a charging-system problem.

   • How would you interpret abnormal readings?
8. What precautions should you take when turning on electrical equipment, especially avionics?

   Follow the starting and avionics checklist to avoid unnecessary electrical loads and protect sensitive equipment.

9. How is the starter powered, and what precautions should you take during engine start?

   The battery normally supplies its high current. Clear the propeller area and observe the starter’s operating-time limits.

Scenario-Based Questions

1. You notice the ammeter is showing a discharge in flight. What does this indicate, and how do you respond?

   The battery is supplying more current than it is receiving. Check the charging system, reduce electrical demand and follow the checklist.

2. The alternator warning light comes on during flight. What steps will you take to troubleshoot?

   Use the alternator-failure checklist, reduce unnecessary electrical loads and plan an appropriate landing.

3. If you lose all electrical power, which instruments and systems will still function?

   Mechanical controls, the magnetic compass and conventional pitot-static instruments can still work. Other instruments depend on their power and backup sources.

4. What actions would you take if a circuit breaker pops? Can you reset it?

   Follow the airplane’s checklist. Do not automatically reset it; a reset must be justified by the procedure or safe-flight need.

5. Describe what happens if you inadvertently run the battery down during preflight. What steps will you take to ensure a safe flight?

   Have it properly charged or serviced and verify normal starting and charging before departure.

6. You experience electrical system anomalies, such as flickering lights or erratic instrument behavior. How would you diagnose the problem?

   Check the electrical indications and follow the checklist. Treat repeated warnings or tripped breakers as a fault, not something to keep resetting.

7. What would you do if an overvoltage condition is detected?

   Follow the overvoltage checklist and isolate the faulty charging source as directed.

8. You are in IMC, and the electrical system fails. What systems can you rely on?

   Use the installed independent and backup instruments. A conventional panel may retain vacuum gyros and pitot-static instruments; know your actual panel.