Oil consumption trend plus an intermittent filter bypass light at an outstation
You are the flight engineer on a Kenyan-registered twin turboprop freighter flying a five-sector day. At the second stop the sector report shows No. 2 engine oil consumption of 0.45 US qt/h against an AFM limit of 0.50 qt/h; the trend over the last 200 h has risen from 0.12 to 0.44 qt/h. In the cruise at maximum climb power the No. 2 oil filter impending-bypass light flickered twice, for a few seconds each time; it did not illuminate in the descent or during the ground run. The outstation AME is not type-rated but has removed the chip detector: it shows fine grey fuzz, with no flakes or balls. The AMM states: fuzz only - clean, refit and re-inspect within 25 h; flakes or particles - remove the engine from service; impending-bypass light - replace the filter element and inspect the housing before further flight. The outstation holds no replacement element. Main base is two sectors and 3 h 10 min away. Two sectors remain on the schedule and the operator is pressing to complete both.
1. Make the dispatch decision for the remaining two sectors and justify it against the maintenance data and the MEL.
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The aircraft does not go. Each piece of evidence is survivable on its own; together they are not.
Start with the AMM instruction, which is the controlling document: an impending-bypass indication calls for element replacement and housing inspection before further flight. That is a hard before-flight action, not a recommendation, and it is not an MEL item - you cannot defer a filter bypass because a bypass means unfiltered oil is reaching the bearings, with the debris it carries. The chip detector fuzz is acceptable in isolation, but it is not reassuring in combination: fuzz plus a rising consumption trend plus bypass indications points at internal wear generating particulate.
The consumption figure is at 90 % of the limit with a trend that has almost quadrupled in 200 h. Even if the bypass had not appeared, that trend is a signal to investigate, not to fly 3 more hours.
The argument that the light only flickers at high power is exactly the argument not to accept it: maximum climb power is where the oil system works hardest and where a filter already near bypass will stay bypassed, with the highest oil temperatures of the sector ahead.
So either the element and the type-rated AME come to the aircraft, or the aircraft moves only under a specific approval - which is a maintenance and continuing-airworthiness decision with the KCAA, not an operational one made at the airstrip.
2. What would you do if the light came on steady in the cruise, and what does that indicate about the oil system?
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A steady light means the filter is fully bypassed, so unfiltered oil is circulating continuously. The immediate actions are procedural, not diagnostic: reduce power to the minimum practical, keep oil temperature and pressure under close watch, and plan to land at the nearest suitable aerodrome rather than continue to a more convenient one. Advise ATC and the company, brief the cabin crew and prepare for an in-flight shutdown and single-engine diversion.
Why land rather than monitor: the filter has already failed its function. The debris that blocked it is now being carried into the bearings and the governor, and the next indication may be a pressure fluctuations or a rise in temperature rather than a light. Once oil pressure starts to fluctuate the engine may not be recoverable and you will be managing a shutdown at a time and place not of your choosing.
If the light goes out after power reduction, that does not clear the aircraft: it confirms the bypass was flow-related and the element still must be replaced before the next flight. Record the power setting, altitude, oil temperature and pressure at the time of illumination - the maintenance investigation needs those numbers.
3. Set out the records, approvals and reporting that must follow, and who signs what.
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Sequence and sign-off matter as much as the decision.
Technical log: a specific entry for the No. 2 oil filter impending-bypass indication, including phase of flight, power setting, duration and oil temperature/pressure, plus the chip detector finding and the consumption trend figures. The outstation AME signs for the inspection he actually performed - chip detector removal, cleaning and refit - not for the filter, which was not changed.
Maintenance: the element replacement and housing inspection are certified in the engine log by type-rated personnel, followed by a Certificate of Release to Service before the aircraft returns to line. The operator's continuing-airworthiness manager must be informed the same day so the consumption trend is reviewed against the manufacturer's data and the engine condition-monitoring programme.
Approvals: no MEL, CDL or commander's discretion cures a before-further-flight inspection. If a positioning or ferry flight were ever considered with a known oil-system defect, it requires a specific approval with defined restrictions - not a line decision.
Reporting: if the outcome is an in-flight shutdown, an air turnback or a precautionary landing, it goes into the operator's SMS and to the KCAA as a reportable occurrence within the prescribed period. The FE's report and the AME's findings should cross-reference each other.