M250-C20B Oil Consumption and Chip Detector Warning
An M250-C20B powers a Bell 206B on scenic flights from a remote South Island base. At the 100-hour inspection the engineer finds the oil filter impending-bypass indicator popped, the chip detector has a small fuzz but no flake, and oil pressure has fluctuated between 60 and 75 psi in cruise, where it normally sits steady at 70 psi. Oil consumption has risen from 0.1 to 0.45 US quart per hour over the last 25 hours. Spectrometric analysis shows iron 55 ppm (fleet baseline 10 ppm), nickel 18 ppm, chromium 6 ppm and aluminium 4 ppm. The last oil change was 30 hours ago. The operator has a charter booked in four hours and asks whether the aircraft can be ferried 25 minutes to the main base for inspection. The engine has 3,200 hours since overhaul. The maintenance manual requires inspection of the filter and chip detector for metal and defines oil-consumption limits. The engineer has a borescope but no spare engine at the remote base.
1. Evaluate the evidence and decide whether the aircraft is airworthy for the proposed 25-minute ferry. Give your reasoning.
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The evidence points to internal engine distress, not a routine oil-consumption change. The impending-bypass indicator has popped, so the filter is close to bypassing; after bypass, unfiltered oil can carry debris to bearings. The chip detector has fuzz, which can be normal, but combined with rising consumption, fluctuating pressure and elevated iron, nickel and chromium it is significant. Oil pressure fluctuation suggests a bearing or oil-pump/relief-valve problem. The iron at 55 ppm is more than five times baseline, and the nickel and chromium support bearing or gear wear. A 25-minute ferry is not a safe option: a bearing failure in flight can cause seizure, fire or loss of the engine, and the remote base has no spare. The manual requires filter and chip-detector inspection; the bypass condition alone warrants investigation before flight. My decision is to not release the aircraft for the charter or the ferry. Cancel the charter, inspect on site, and if the filter contains flakes or the chip detector has significant metal, remove the engine. A ferry permit would not make an unairworthy engine airworthy.
2. Identify the likely component(s) and explain what the metal signature and other symptoms suggest. What inspections and tests would you carry out?
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The combination suggests a main bearing, gearbox bearing or oil-pump failure rather than a single isolated wear particle. Iron and chromium are consistent with bearing races, rollers and steel gears; nickel can come from gearbox or shaft components; aluminium may come from the oil pump or accessory housing. Rising consumption with pressure fluctuation points to increased clearances or a failing seal or pump. The filter bypass tells you the debris load is high. On site: cut the filter and inspect the pleats; clean and inspect the chip detector; check magnetic plugs; check the oil-pump relief valve; measure oil pressure with a calibrated gauge; borescope the oil sump and accessible bearing areas if the manual permits; repeat spectrometric analysis after a ground run only if the manual allows. Do not simply clean the chip detector and release. If the filter has flakes, or the chip detector has a flake rather than fuzz, the engine is unserviceable.
3. If the filter contains significant ferrous flakes, what release decision and records follow?
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Significant ferrous flakes mean the engine has failed internally and cannot be released to service. The correct action is to quarantine the engine, preserve the filter and chip detector as evidence, make a log entry, notify the CAMO and operator, and arrange engine removal and overhaul. The aircraft can be released only after a serviceable engine is installed and the appropriate maintenance release is issued. Record the findings, oil analysis, filter inspection, chip-detector condition and the reason for removal. If the operator wants a ferry to maintenance, that would require an approved ferry arrangement and engineering assessment; it should not be done with a known failing bearing. The charter must be cancelled. A clean-and-recheck is only acceptable for normal fuzz, not for flakes with bypass and rising consumption.