Chip Light After a Starter-Generator Change
A PT6A-powered turboprop has just had its starter-generator replaced. On the first ground run afterward, the chip detector caution annunciator illuminates. You remove the chip detector: the tip is covered in fine, hair-like ferrous whiskers, and there is also one discrete bright metallic particle about 0.5 mm across. The engine has 1,200 hours since new. The oil filter was changed 20 hours ago and was clean at that time. The engine maintenance manual states that fine fuzz may be cleaned off and the detector returned to service, that the presence of particles or flakes requires the further inspections listed in the manual, and that the oil filter element and oil screen must be examined whenever metal is found.
1. Describe how you characterize what is on the chip detector and the inspection sequence you would run.
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Separate the two findings, because they mean different things:
- Fuzz - fine, hair-like whiskers that cling to the magnet and wipe off as a smear. Common after maintenance and during break-in of a newly installed component.
- Particle - a discrete, identifiable piece. Yours is about 0.5 mm, which is not fuzz.
Sequence:
- Wipe the detector onto a clean white cloth and examine under magnification; test with a magnet to determine ferrous versus non-ferrous.
- Cut open the oil filter element and inspect the pleats for metal; check the oil screen/accessory gearbox strainer.
- Compare any findings against the manual's size/count criteria.
- Consider the recent maintenance as a possible source: a new starter-generator can shed fuzz as it seats in, which plausibly explains the whiskers but does not explain a discrete particle.
- If the particle is non-ferrous, note that the magnetic plug cannot be relied on to catch that material - the screens and filter become the primary evidence.
2. Can you release the aircraft? Give the decision logic rather than a yes or no.
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Decision logic:
- Fuzz only and a clean filter/screen: clean and reinstall the detector per the manual, run the engine, recheck, and comply with any manual-specified repeat inspection interval. Release is generally supportable with that documented.
- Fuzz plus a discrete particle: you are outside the 'fuzz only' allowance. Apply the manual's particle criteria. If the particle exceeds the stated limits, or if you cannot establish its source and show it is benign, the aircraft is not released - perform the manual's follow-on inspections (filter and screen examination, oil analysis, borescope or accessory gearbox inspection as directed).
You are not required to prove the engine is failing, only to show it meets its approved data before approving return to service. A clean filter 20 hours ago helps, but it does not cover the last 20 hours. Do not clean the plug and walk away from an unexplained particle.
3. The operator says, 'Chip lights do that all the time - just clean it and sign it off.' How do you handle it?
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Politely, but firmly: 'it happens all the time' is not a basis for approval. The manual defines what may be cleaned and returned to service (fuzz) and what triggers further inspection (particles). You found a particle, so the second path applies.
If you clean the detector, reinstall it, and sign the aircraft off, the decision and its consequences are yours. The record must describe what was actually found - fuzz plus a 0.5 mm particle - what was done, and the data used, per 14 CFR 43.9. If the manual requires a follow-up chip check after a specified interval and the operator will not commit to it, the discrepancy stays open and the aircraft is not in compliance.
Offer the alternatives: complete the additional inspections now, or leave the aircraft down. What you cannot do is convert an unresolved metal finding into a clean sign-off under schedule pressure.