AET Electrical Troubleshooting 4 — Questions and Answers
Question 1: A strobe light on an aircraft fails to flash but the power supply capacitor charges correctly. The fault most likely lies in the:
- Power supply rectifier
- Flash tube or trigger circuit (Correct answer)
- Aircraft bus voltage
- Main generator
Correct answer: Flash tube or trigger circuit
If the capacitor charges correctly but the light fails to flash, the flash tube, trigger transformer, or trigger circuit is likely faulty.
Question 2: When checking a shorted wiring harness, a technician should use a/an:
- High-voltage megohmmeter at 500V
- Standard ohmmeter to check pin-to-pin resistance (Correct answer)
- Clamp-on ammeter around the harness
- Frequency counter
Correct answer: Standard ohmmeter to check pin-to-pin resistance
A standard ohmmeter can detect pin-to-pin shorts within a harness by revealing unexpectedly low resistance between conductors that should be isolated.
Question 3: Aircraft wiring that shows discoloration (brown or black insulation) most likely indicates:
- Normal aging of the insulation material
- Overheating due to excessive current or poor connection (Correct answer)
- Exposure to hydraulic fluid
- Correct wire gauge for the application
Correct answer: Overheating due to excessive current or poor connection
Discolored or charred insulation is a sign of overheating, caused by overcurrent, high-resistance connections, or incorrect wire gauge.
Question 4: A ground return circuit fault in aircraft wiring most commonly causes:
- Overcurrent in the affected circuit
- Reduced voltage at the load and erratic equipment operation (Correct answer)
- Tripped circuit breakers on multiple buses
- Reversed polarity at the equipment terminals
Correct answer: Reduced voltage at the load and erratic equipment operation
A poor ground return adds resistance in series with the load, causing a voltage drop that results in reduced voltage at the equipment and erratic operation.
Question 5: An ammeter is connected in series with an aircraft circuit to check current flow. When the circuit is activated, the meter reads zero. This indicates:
- Normal low-current operation
- An open circuit between the power source and the load (Correct answer)
- A short circuit in the wiring
- Correct operation at idle
Correct answer: An open circuit between the power source and the load
Zero current in an energized series circuit indicates an open that prevents current from flowing through the ammeter and load.
Question 6: During troubleshooting, a technician finds that an aircraft navigation light works normally on the ground but fails in flight. The MOST likely cause is:
- An intermittent open caused by vibration or thermal expansion (Correct answer)
- A faulty circuit breaker that only trips in flight
- Reduced generator output at cruise RPM
- Antenna interference with the lighting circuit
Correct answer: An intermittent open caused by vibration or thermal expansion
Vibration, thermal cycling, or connector movement in flight can cause intermittent opens that are not present under static ground conditions.
Question 7: The purpose of performing a 'split-half' troubleshooting method on a long wiring run is to:
- Replace half the wiring at a time to reduce cost
- Efficiently isolate the fault location by testing the midpoint first (Correct answer)
- Test both ends of the wiring simultaneously
- Verify wire gauge is consistent throughout the run
Correct answer: Efficiently isolate the fault location by testing the midpoint first
Testing the midpoint of a circuit first eliminates half the possible fault locations with each measurement, minimizing total tests required.
AET Electrical Troubleshooting 4
A strobe light on an aircraft fails to flash but the power supply capacitor charges correctly.
The fault most likely lies in the: