During morning inspection after an overnight period of UMS operation the following changes were detected:

Possible causes:

• A developing fault in a cylinder (e.g. a faulty injector, a stuck ring, or a leaking exhaust valve) causing abnormal combustion noise.
• A bearing problem (e.g. a main or big-end bearing starting to wipe) causing a knocking noise.
• A change in the fuel (e.g. water or sludge in the fuel) causing rough combustion.
• A turbocharger problem (e.g. surging or a bearing fault) causing a change in the noise.
• A piston/liner problem (e.g. scuffing) causing a change in the noise.

How normal operations might be restored: investigate the cause - check the exhaust temperatures of all cylinders, listen for abnormal noise, check the fuel system (filters, pumps, injectors), the governor, and the turbocharger. Rectify the fault (e.g. replace a faulty injector, change the fuel, adjust the governor) and restore the engine to normal.

Possible causes:

• A governor fault or a change in the fuel supply (e.g. a blocked filter or a faulty fuel pump) causing the speed to vary.
• A change in the load (e.g. a change in the propeller or the electrical load) causing the speed to change.
• A fault in a cylinder (e.g. a misfiring cylinder) causing the engine to lose power and the speed to drop.
• A governor set-point change or a control system fault.

How normal operations might be restored: investigate the cause - check the governor, the fuel supply (filters, pumps), the load, and the cylinders. Rectify the fault (e.g. clean the filter, adjust the governor, rectify the cylinder fault) and restore the engine to normal.

Possible causes:

• A faulty injector (over- or under-fueling a cylinder) causing that cylinder's exhaust temperature to rise or fall.
• A leaking exhaust valve or a loss of compression in a cylinder.
• A change in the fuel quality or the load distribution.
• A scavenge fire or a turbocharger problem affecting the air supply.

How normal operations might be restored: investigate the cause - check the exhaust temperatures of all cylinders, check the injectors, the exhaust valves, the compression, and the fuel. Rectify the fault (e.g. replace a faulty injector, re-seat an exhaust valve, adjust the load distribution) and restore the engine to normal. If a scavenge fire is suspected, take the appropriate action (reduce load, stop the engine if necessary, and extinguish the fire).