AET Electrical Troubleshooting 5 — Questions and Answers
Question 1: An aircraft pitot heat circuit draws 8 amps normally but now draws only 2 amps with full voltage applied. This most likely indicates:
- A short circuit in the heater element
- An open or partial open in the heater element increasing resistance (Correct answer)
- A failed circuit breaker
- Low bus voltage from the generator
Correct answer: An open or partial open in the heater element increasing resistance
Lower-than-normal current with correct voltage indicates increased resistance, such as a partially open or deteriorated heating element.
Question 2: When troubleshooting a faulty fuel quantity indicator, a technician should verify the sender resistance by:
- Measuring voltage at the indicator terminals
- Disconnecting the sender and measuring resistance at the sender connector pins (Correct answer)
- Applying full power and observing indicator deflection
- Replacing the indicator first, then the sender
Correct answer: Disconnecting the sender and measuring resistance at the sender connector pins
Disconnecting the sender and measuring its resistance directly verifies whether the sender or indicator is faulty before replacing components.
Question 3: A transponder fails the ramp test for Mode C altitude encoding. After confirming the transponder is serviceable, the technician should check the:
- Antenna coax cable only
- Encoding altimeter or blind encoder and associated wiring (Correct answer)
- Aircraft compass system
- Pitot-static drain valves
Correct answer: Encoding altimeter or blind encoder and associated wiring
Mode C altitude data comes from the encoding altimeter or blind encoder — a wiring or encoder fault will cause incorrect altitude reporting despite a serviceable transponder.
Question 4: A technician measures 0 ohms between the positive terminal of an aircraft component and aircraft ground with the circuit de-energized. This indicates:
- A normal low-resistance ground path
- A direct short circuit to ground in the component or wiring (Correct answer)
- An open circuit in the component
- Correct bonding resistance per FAA standards
Correct answer: A direct short circuit to ground in the component or wiring
Zero resistance between a positive circuit terminal and ground (with the circuit de-energized) indicates a direct short to ground that would blow fuses or trip breakers when powered.
Question 5: When an aircraft static inverter fails, the FIRST check should be:
- Replace the inverter immediately
- Verify DC input voltage and current draw at inverter input terminals (Correct answer)
- Check AC output frequency with an oscilloscope
- Inspect the output transformer windings for opens
Correct answer: Verify DC input voltage and current draw at inverter input terminals
Confirming correct DC input voltage and current establishes whether the inverter is receiving power before diagnosing internal faults.
Question 6: An aircraft has multiple avionics units failing simultaneously. The technician should first suspect:
- Individual component failures in each unit
- A common power bus, ground, or power supply fault (Correct answer)
- EMI interference from an external source
- Software corruption in each unit
Correct answer: A common power bus, ground, or power supply fault
Simultaneous failure of multiple units sharing a common bus or ground points to a single upstream fault rather than multiple independent component failures.
Question 7: During a resistance check of an aircraft wiring harness connector, a technician finds 0.8 ohms on a pin that should measure below 0.1 ohms. The BEST corrective action is to:
- Accept the reading as it is below 1 ohm
- Clean or replace the connector to restore proper contact resistance (Correct answer)
- Install a heavier gauge wire to compensate
- Apply additional voltage to burn through the resistance
Correct answer: Clean or replace the connector to restore proper contact resistance
Connector contact resistance above specification indicates contamination, corrosion, or wear that requires cleaning or connector replacement to prevent voltage drop and heat buildup.
AET Electrical Troubleshooting 5
An aircraft pitot heat circuit draws 8 amps normally but now draws only 2 amps with full voltage applied.
This most likely indicates: