AN SA227 METROLINER FO RPTS THE REMOTE POSSIBILITY OF HAVING REVERSED BOTH ENGS INFLT.

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DURING A VISUAL APCH; APCH CTL REQUESTED 'MAX FORWARD SPD UNTIL FINAL; AND KEEP YOUR BASE IN CLOSE.' THUS; I KEPT THE INDICATED AIRSPD AT JUST UNDER VMO. I KNEW THE ONLY WAY TO BLEED THE SPD OFF IN TIME TO CONFIGURE FOR LNDG WAS TO RAPIDLY BRING THE PWR LEVERS ALL THE WAY BACK TO THE FLT IDLE STOPS (THUS SOUNDING THE GEAR WARNING HORN). AS I WAS ABOUT TO TURN FINAL; I BEGAN QUICKLY RETARDING THE FLT LEVERS. THE GEAR WARNING HORN SOUNDED AS EXPECTED AND I CONTINUED TO RETARD THE PWR LEVERS EXPECTING TO HIT THE FLT IDLE STOPS. HOWEVER; BEFORE I HIT THE STOPS; THE PROPS MADE A LOUD SOUND SIMILAR TO THAT OF WHEN THEY GO INTO REVERSE. WHEN THIS HAPPENED; I QUICKLY PUSHED THE PWR LEVERS BACK FORWARD UNTIL THE GEAR HORN STOPPED SOUNDING. I THEN NOTICED THE IGNITION LIGHTS WERE ILLUMINATED (INDICATING THE PROPS HAD SENSED A NEGATIVE TORQUE CONDITION). I DID NOT NOTICE WHAT AIRSPD WE HAD SLOWED TO BUT CONTINUED TO SLOW THE AIRPLANE; CONFIGURED FOR LNDG; AND LANDED WITHOUT INCIDENT. ONCE ON THE GND; I REVIEWED THE SIT WITH THE CAPT AND DISCUSSED CERTAIN SCENARIOS. THE ONLY OPTION I COULD THINK OF WAS THAT I HAD LIFTED THE FLT IDLE LOCKS THUS ALLOWING THE PWR LEVERS TO GO BEYOND FLT IDLE INTO GND IDLE. THIS OPTION DIDN'T MAKE SENSE FOR 2 REASONS. DURING OUR POSTFLT; WE ASKED A MECH WHAT HIS THOUGHTS ON THE SIT WERE. HE SAID THAT AT THAT AIRSPD IF THE PROPS WERE CRUISED UP (96% RPM -- WHICH THEY WERE) AND THE PWR LEVERS WERE BROUGHT BACK VERY QUICKLY; THEN THE PROP GOVERNOR COULD POSSIBLY SENSE A CONFLICT BY RESCHEDULING THE FUEL CTL UNIT (WHICH OCCURS ABOUT 97.5% RPM) BTWN THE PROP GOVERNOR AND THE UNDERSPD GOVERNOR; THEREBY CAUSING SOME ERRATIC PITCH CHANGES IN THE PROP WHICH COULD SIMULATE REVERSE MODE. THIS SCENARIO SEEMED THE MORE LIKELY SCENARIO BECAUSE OF THE REASONS STATED EARLIER. HOWEVER; I HAVE PLAYED THE EVENTS OVER AND OVER IN MY MIND AND I CANNOT DETERMINE DEFINITIVELY WHETHER OR NOT I TOUCHED THE LOCKS OR WHETHER OR NOT THE PWR LEVERS WERE BROUGHT INTO GND IDLE.