Describe a time you diagnosed and fixed an intermittent avionics fault on an aircraft system or test rig.
Technical
Troubleshooting
Test Equipment
Electronic Diagnostics
Intermittent faults are common in avionics and can be the hardest to reproduce and resolve. For a junior avionics engineer, demonstrating systematic troubleshooting, use of test equipment, and adherence to safety and certification standards (e.g. DO-178C for software, DO-254 for hardware) is critical.
How to answer
- Use the STAR structure: Situation, Task, Action, Result.
- Start by briefly describing the system (e.g., flight control computer, navigation sensor, communication radio) and why the fault mattered for safety or operations.
- Explain how you collected data: logs, fault codes, test rig results, bench tests, or flew ground runs if applicable.
- Detail the diagnostic process: hypothesis generation, instrumentation used (oscilloscope, logic analyzer, spectrum analyzer, multimeter), isolation steps, and any repeatable test you established.
- Mention collaboration with senior engineers, maintainers, or OEM support (e.g., contacting an ST Engineering or Collins Aerospace application engineer) and how you followed maintenance procedures and safety rules.
- Conclude with the fix applied, validation steps taken, and measurable outcome (reduced failures, restored serviceability, lessons learned).
What not to say
- Claiming you fixed it by guesswork or trial-and-error without systematic testing.
- Taking sole credit for a team effort or omitting reference to approvals and safety checks.
- Skipping mention of applicable standards, documentation updates, or validation after the fix.
- Focusing only on tools used without explaining reasoning and results.
Sample answer
“At a component-level test rig in my internship at ST Engineering, we experienced an intermittent loss of GPS lock on a navigation module used for a UAV demonstrator. The issue happened roughly once every 20 hours and could not be reproduced in basic bench tests. I collected timestamped error logs and synchronized them with power and RF environment logs. I hypothesised a power rail glitch during certain transmit cycles. Using an oscilloscope and a high-speed current probe, I observed a brief voltage dip on the 3.3 V rail coinciding with the fault. Working with a senior engineer, we traced the dip to a marginal decoupling capacitor on the power board. After replacing the capacitor and adding an additional decoupling network, the GPS lock failures stopped during a 100-hour stress test. We updated the maintenance bulletin and test procedures. Through this process I learned the importance of correlating logs, using the right instrumentation, and validating fixes under representative conditions.”
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