AN SF340 PILOT REPORTS AN INCORRECT PROP AND ENG LOW OIL PRESS WARNING FAULT WHEN THE ENG IS FEATHERED FOR GND COOLING.

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I BELIEVE 2 WRITE-UPS WERE MISCOMMUNICATED BY ALL AND THEREFORE NOT PROPERLY ADDRESSED. OPERATED ACFT FROM ZZZ TO ZZZ1; IT WAS NON-EVENTFUL UNTIL TAXIING INTO ZZZ1 WITH THE #2 ENG IN FEATHER. FOR COOLING OPS WE ELECTED TO FEATHER THE ENG AND INCREASE COOLING EFFICIENCY FOR PAX AND CREW COMFORT WITH HP BLEED USE. WHEN FEATHERED THE CENTRAL WARNING PANEL INDICATED A LOW OIL PRESSURE WARNING WHICH WE THEN FOLLOWED THE QRH WHICH LED US TO SHUT DOWN THE ENG AND TAXI TO THE OUTSIDE PARKING SPOT WHERE EVERYONE WAS DEPLANED AS ANY NORMAL FLT DOES. AS PIC I EXPRESSED MY CONCERNS OF GETTING THE LOW OIL PRESSURE LIGHT DURING FEATHERED OPS AND TALKED WITH MAINT THAT THIS INDICATION IS NOT WHAT IS NORMALLY EXPERIENCED. THE ENG PARAMETERS WERE ALL NORMAL AND THE PROP WAS TOO UNTIL BROUGHT INTO FEATHER WHEN THE ENG LOW OIL PRESSURE WAS ILLUMINATED AND THE PROP OIL THEN INDICATED 0. I THEN RETURNED TO THE ACFT FOR THE NEXT FLT AND THE ACFT HAD BEEN INSPECTED AND OPERATED AND SIGNED OFF READY FOR OUR NEXT FLT TO ZZZ2. I WAS INSTRUCTED TO REF OUR MANUAL AND FOLLOWED OUR LIMITATIONS IN CHAPTER 1 FOR THE NEXT FLT AND TOOK A SMALL DELAY IN VERIFYING THE PROPER PAPERWORK AND PROCS WITH LINE MAINT. BOTTOM OF THE PAGE: IF THE WARNING GOES OUT WHEN THE CL IS MOVING TO UN-FEATHER; THE WARNING CAN BE DISREGARDED. DO NOT OPERATE PROLONGED TIME WITH THE PROP IN FEATHER AND THE WARNING DISPLAYED. THE ACFT OPERATED NORMALLY AND NO OIL PRESSURE LIGHTS ILLUMINATED DURING THE TAXI OR FLT TO ZZZ2. DURING TAXI TOWARDS THE ZZZ1 RAMP AFTER LNDG I AGAIN FEATHERED THE #2 ENG FOR COOLING PURPOSES AND PROCEEDED TO GET THE MASTER WARNING AND LOW OIL PRESSURE LIGHT AND FOLLOWED THE QRH. WE TAXIED IN UNEVENTFUL TO THE GATE. I WROTE UP THE DISCREPANCY TO THE BEST OF MY ABILITIES AND ASKED MAINT IF THIS COULD BE LOOKED AT CLOSER. I RETURNED FOR THE CONTINUATION OF FLT FROM ZZZ1 TO ZZZ3 NEXT AND REEVALUATED THE LOGBOOKS WITH THE LINE MAINT BEFORE TAKING ACFT TO ZZZ2. I WAS GIVEN GUIDANCE THAT IT WAS ACCEPTABLE AND THAT THE ACFT WAS READY FOR SVC. WE FLEW WITHOUT ANY ABNORMAL INDICATIONS TO ZZZ3. THE NEXT MORNING WE FLEW THE ACFT BACK TO ZZZ1 AND A WHITE STATUS LIGHT CAME ON THE OVERHEAD PANEL WHICH IS UNLABELED EXCEPT WITH 2 PARALLEL LINES ON IT ABOVE THE FUELING LIGHT. IT LATER EXTINGUISHED AND NEVER GAVE US ANY INDICATION OF ANY MALFUNCTION AT ANYTIME. WE PARKED THE ACFT AND DURING OUR SHUTDOWN SEQUENCE OF FEATHERING THE PROPS THE #2 ENG OIL PRESSURE LIGHT ILLUMINATED WITHOUT A MASTER WARNING CHIME WHICH IS ABNORMAL. I PROCEEDED TO DOCUMENT THE INDICATIONS IN THE LOG AND WAS TO FINISH THE 3 DAY TRIP ON ANOTHER ACFT UNEVENTFUL. AFTER RETURNING TO ZZZ1 FROM THE END OF OUR TRIP I DISCUSSED THE WRITE-UPS FURTHER WITH LINE MAINT AND CAME TO THE CONCLUSION THE LOW PROP OIL PRESSURE SENSOR WAS GIVING ABNORMAL INDICATIONS WITH THE PROP FEATHERED. THE ACFT WAS NOW RETURNED TO SVC OPERATING NORMAL DURING FEATHERED OPS. PLTS; MAINT AND MGMNT WERE ALL GIVEN THE PROPER INFO AND THE ACFT WAS THEN PROPERLY ADDRESSED. THE FIRST 2 WRITE-UPS MAY HAVE BEEN MISUNDERSTOOD AND NOT ASSOCIATED WITH THE PROPER OP OF THE ENG WHILE IN FEATHER. MOST 121 ACFT OPERATE SMOOTHLY WITH LITTLE TO NO CENTRAL WARNING PANEL LIGHTS ILLUMINATING UNLESS SOMETHING NEEDS TO BE ADDRESSED. THE SAAB 340 IS NO DIFFERENT BUT CAN OCCASIONALLY HAVE THE LOW OIL PRESSURE LIGHTS ILLUMINATE DUE TO LACK OF PROP SPD AND THEREFORE PRESSURE BUILDUP IN THE FEATHERED POS. WE HAVE BEEN TRAINED TO PROPERLY IDENT THIS AND OPERATE THEM WITH THIS OCCASIONAL OCCURRENCE. SOME OF THIS TRAINING CAN BE ASSOCIATED WITH EXPERIENCE. THE ACFT CAN GIVE THIS WARNING DURING START UP OR SHUTDOWN OF 1 FLT AND MAY NOT REPEAT ITSELF THE FOLLOWING DAYS YOU FLY IT AND WORK EXCEPTIONALLY WELL THEREAFTER. WE ALSO HAVE GUIDELINES IN OUR MANUAL THAT SAY: 'DO NOT OPERATE PROLONGED TIME WITH THE PROP IN FEATHER AND THE WARNING DISPLAYED.' THIS ACFT WAS THE EXCEPTION TO THE NORM AND HAD A FAILURE NOT NORMALLY SEEN. IT CAME ON AND GAVE WARNINGS DURING FEATHEREDOPS DIVIDING OUR ATTN MOMENTARILY WHILE TAXIING TO THE GATE AND THAT IS WHY I FOLLOWED THE PROCS IN THE QRH WHICH LEADS TO THE SHUTDOWN AND WRITE-UP IN THE LOGBOOK. AVOIDING THIS EVENT OF A MISCOMMUNICATED WRITE-UP OF THE PROP LOW OIL PRESSURE SENSOR IS A DIFFICULT TASK AND NEEDS TO BE MADE AWARE OF BY ALL INVOLVED. HAVING A SENSOR NOT SENSING PROPERLY IS AN ADDED DISTR.