FAA Aviation Mechanic Powerplant (AMP)Fuel, Induction and LubricationHard
An oil analysis laboratory reports increasing concentrations of iron and chromium in successive spectrometric oil analysis (SOAP) samples from a reciprocating engine, while other metals remain stable. What should the mechanic suspect based on this trend?
- AContamination from an improperly cleaned oil sample container
- BNormal wear from bronze or brass bushings in the accessory section
- CPossible wear of steel components such as cylinder walls, piston rings, or camshaft/lifters
- DNormal break-in wear that requires no further investigation
Show answer & explanationAnswer & explanation
Correct answer: C. Possible wear of steel components such as cylinder walls, piston rings, or camshaft/lifters
Spectrometric oil analysis identifies trace metal concentrations in engine oil to detect abnormal wear before failure occurs. Iron and chromium are typically associated with steel and chrome-plated components such as cylinder walls, piston rings, camshafts, and lifters, so an increasing trend in these elements indicates potential wear in those parts requiring further investigation.
Why the other options are wrong
- A. Container contamination would typically show random inconsistent results, not a consistent increasing trend across multiple samples.
- B. Bronze/brass wear would show increased copper, tin, or zinc, not iron and chromium.
- D. An increasing trend, especially in a mature engine, is not dismissed as simple break-in wear without further investigation.
Spectrometric Oil Analysis (SOAP)
A laboratory technique that measures trace metal content in engine oil to detect abnormal internal wear trends before component failure occurs.
- Iron/chromium indicate steel or chrome-plated part wear (cylinders, rings, cam)
- Copper/tin/silver indicate bearing or bushing wear
- Aluminum indicates piston or crankcase wear
- Trend analysis over multiple samples is more valuable than a single reading
Memory trick: Iron and chrome climbing = steel parts grinding down inside