While climbing through 7,000 ft the engine indicating system, low oil pressure caution light, illuminated. With the oil pressure indication fluctuating around 90 pounds per square inch, and the caution light flickering, the pilot in command reduced power and elected to return to Port Augusta. During descent the warning light continued to flicker, changes in power setting having no effect. As the aircraft turned on to base leg, the warning light became steady and the oil pressure dropped to less than 60 pounds per square inch. The aircraft made an uneventful landing. Shortly after touchdown, the oil pressure returned to 100 pounds per square inch and the caution/warning lights extinguished.
Investigation by maintenance personnel resulted in an oil filter change due to suspected carbon contamination. The aircraft was then returned to service. The operator raised the recurring oil pressure fluctuation problems with the engine manufacturer.
The Pratt & Whitney PT6 engine model installed in the PC12 has experienced episodes of oil discolouration, and carbon particles in the oil. The discolouration was traced to the coatings in the magnesium gearbox, and the carbon was traced to the No. 2 bearing area.
Further investigation of the fluctuating oil pressure indications revealed a fault in the main engine wiring loom.
Local safety action
The operating company repaired the faulty wiring loom and checked the other aircraft in the fleet for similar problems.
Safety action by the engine manufacturer
The engine manufacturer has initiated an oil and oil filter analysis program across the worldwide fleet, in an ongoing product improvement program to remedy the discolouration and particulate problems.
Bureau of Air Safety Investigation safety action
The Bureau is monitoring the analysis program.
|Date:||20 October 1998||Investigation status:||Completed|
|Time:||0230 hours CST|
|Location:||19 km SSE Port Augusta, (NDB)|
|State:||South Australia||Occurrence type:||Abnormal engine indications|
|Release date:||15 July 1999||Occurrence category:||Incident|
|Report status:||Final||Highest injury level:||None|
|Aircraft manufacturer||Pilatus Aircraft Ltd|
|Type of operation||Aerial Work|
|Damage to aircraft||Nil|
|Departure point||Port Augusta, SA|
|Departure time||0230 hours CST|