AET Diagnostic and Testing Tools 2 — Questions and Answers
Question 1: When using a clamp-on ammeter to measure AC current in an aircraft wiring harness, the technician should ensure which of the following?
- Only one conductor passes through the clamp jaw (Correct answer)
- All conductors in the bundle pass through the clamp jaw
- The meter is set to DC mode before clamping
- The circuit breaker is pulled before clamping
Correct answer: Only one conductor passes through the clamp jaw
A clamp-on ammeter measures the magnetic field produced by a single conductor; placing multiple conductors cancels their fields and gives a false reading.
Question 2: A Time Domain Reflectometer (TDR) is primarily used in aircraft maintenance to:
- Measure insulation resistance of wire bundles
- Locate faults and determine their distance in coaxial or wire runs (Correct answer)
- Test continuity of bonding straps
- Calibrate altimeter static ports
Correct answer: Locate faults and determine their distance in coaxial or wire runs
A TDR sends a pulse down a conductor and analyzes the reflected signal to pinpoint fault location and distance.
Question 3: Which instrument is the correct tool for verifying the output frequency of an aircraft inverter?
- Digital multimeter set to AC volts
- Frequency counter or oscilloscope (Correct answer)
- Megohmmeter
- Capacitance bridge
Correct answer: Frequency counter or oscilloscope
A frequency counter or oscilloscope directly measures the cycles per second of an inverter's AC output.
Question 4: A logic probe displaying a steady LOW on a digital avionics bus line most likely indicates:
- Normal bus activity with data present
- The line is being held at ground potential or is open (Correct answer)
- An intermittent short to power
- The probe battery is discharged
Correct answer: The line is being held at ground potential or is open
A steady LOW typically means the line is being actively pulled to ground or is open with a pull-down resistor.
Question 5: What is the primary purpose of a breakout box in avionics troubleshooting?
- To step down high voltage before measurement
- To provide access points to individual pins of a connector without removing it from the LRU (Correct answer)
- To generate test signals into an antenna system
- To balance the impedance of an audio circuit
Correct answer: To provide access points to individual pins of a connector without removing it from the LRU
A breakout box intercepts the connector to expose each pin for measurement while the unit remains in its normal circuit configuration.
Question 6: When performing a capacitor leakage test with an LCR meter on an aircraft power supply filter capacitor, an excessively high leakage current reading indicates:
- The capacitor has too high a capacitance value
- The capacitor's dielectric is degraded or the unit is shorted internally (Correct answer)
- The test leads are reversed
- The power supply output voltage is too low
Correct answer: The capacitor's dielectric is degraded or the unit is shorted internally
High leakage current through a capacitor signals dielectric breakdown or an internal short, requiring replacement.
Question 7: A spectrum analyzer is preferred over a standard oscilloscope when troubleshooting an aircraft VHF communications system because it:
- Displays signal amplitude versus time for waveform capture
- Shows signal energy distribution across frequencies, revealing spurious emissions (Correct answer)
- Measures the total harmonic distortion of audio circuits
- Provides a direct readout of antenna VSWR
Correct answer: Shows signal energy distribution across frequencies, revealing spurious emissions
A spectrum analyzer presents amplitude versus frequency, making it easy to identify harmonic spurs or interference that an oscilloscope cannot easily separate.
AET Diagnostic and Testing Tools 2
When using a clamp-on ammeter to measure AC current in an aircraft wiring harness, the technician should ensure which of the following?