AET Electrical Troubleshooting 3 — Questions and Answers
Question 1: When troubleshooting an intermittent open circuit in an aircraft wiring harness, which method is most effective?
- Replace the entire harness immediately
- Wiggle test while monitoring continuity with an ohmmeter (Correct answer)
- Use a megohmmeter at maximum voltage
- Disconnect all connectors and test each wire individually
Correct answer: Wiggle test while monitoring continuity with an ohmmeter
A wiggle test while monitoring continuity helps isolate intermittent opens caused by broken conductors or poor connections that only fail under movement.
Question 2: An aircraft circuit breaker trips immediately upon reset. The FIRST troubleshooting step should be to:
- Replace the circuit breaker
- Disconnect loads progressively to find the fault (Correct answer)
- Increase the breaker amperage rating
- Check generator output voltage
Correct answer: Disconnect loads progressively to find the fault
Progressively disconnecting loads isolates the faulty component causing the overcurrent condition before replacing the breaker.
Question 3: A voltage drop test across a switch shows 1.8 volts while the circuit is operating. This indicates:
- Normal switch operation
- High resistance in the switch contacts (Correct answer)
- Reverse polarity in the circuit
- An open circuit downstream
Correct answer: High resistance in the switch contacts
Excessive voltage drop across a closed switch indicates high contact resistance due to corrosion, pitting, or wear.
Question 4: Which instrument is used to measure insulation resistance between an aircraft wire and its shield or conduit?
- Multimeter on resistance setting
- Megohmmeter (megger) (Correct answer)
- Clamp-on ammeter
- Oscilloscope
Correct answer: Megohmmeter (megger)
A megohmmeter applies high voltage to reveal insulation degradation that a standard ohmmeter cannot detect.
Question 5: During troubleshooting, a technician measures 28V at one side of a load but 0V at the other side with the circuit energized. This indicates:
- Normal circuit operation
- The load has an open circuit (Correct answer)
- The load has a short circuit
- Excessive current draw
Correct answer: The load has an open circuit
Full supply voltage appearing across an open load (with 0V on the return side) confirms the load element is open and blocking current flow.
Question 6: An aircraft bus bar shows 26V on one side and 24V on the other side under load. The technician should suspect:
- Excessive generator voltage
- A high-resistance connection or corroded bus bar (Correct answer)
- Normal operation within tolerance
- A faulty voltmeter
Correct answer: A high-resistance connection or corroded bus bar
A 2V drop across a bus bar indicates a high-resistance fault such as corrosion, loose hardware, or oxidation at the connection point.
Question 7: When using a logic probe to troubleshoot an aircraft digital avionics circuit, a rapidly flashing LED indicates:
- A steady logic HIGH state
- A steady logic LOW state
- A pulsing or toggling signal (Correct answer)
- No signal present
Correct answer: A pulsing or toggling signal
A rapidly flashing logic probe LED indicates the test point is receiving a pulsing or toggling digital signal rather than a static HIGH or LOW.
AET Electrical Troubleshooting 3
When troubleshooting an intermittent open circuit in an aircraft wiring harness, which method is most effective?