AN ACR EMB120 CREW DSNDING INTO SEA EXPERIENCED AN APPARENT INADVERTENT AUTOFEATHER OF THE #1 ENG.

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I WAS THE PF. WE HAD JUST BEEN GIVEN A LOWER ALT AND A HDG BY ATC TO DSND TO 7000 FT. I CALLED FOR THE DSCNT CHK PER OUR COMPANY'S SOP. THE PNF (CAPT) BEGAN HIS 'DSCNT CHK FLOW PATTERN.' OUT OF THE CORNER OF MY EYE I SAW HIS HAND MOVE UP TO THE OVERHEAD PANEL. THE NEXT THING I KNEW; THERE WAS A MUFFLED 'POPPING' SOUND AND THE PLANE YAWED TO THE L. THE CAPT GRABBED THE CTLS; AND AFTER A FEW SECONDS SAID; 'I THINK WE JUST HAD AN INADVERTENT AUTOFEATHER.' WE INFORMED ATC OF OUR PROB AND DECIDED TO HOLD ON THE LOC WHILE WE TRIED TO DETERMINE WHAT HAPPENED. WHILE I WAS READING THE CHKLISTS (I WAS NOW THE PNF); I NOTICED THAT THE ELECTRIC FEATHER SWITCH ON THE L ENG WAS ON; AND I ASKED THE CAPT IF HE HAD TURNED IT ON. HE SAID HE DIDN'T REMEMBER TURNING IT ON; BUT THAT HE MUST HAVE. THE ACFT WAS VERY CTLABLE AND THE CAPT ELECTED NOT TO SHUT THE ENG DOWN BECAUSE IT WAS GIVING US BLEED AIR AND HYDS AND NOT TO DECLARE AN EMER BECAUSE THE ACFT WAS FLYING FINE. THE ENG WAS NOT BROUGHT OUT OF FEATHER BECAUSE IT APPEARED TO OVERTORQUE. WE LANDED UNEVENTFULLY. IN SPEAKING WITH THE CAPT AFTERWARDS; HE DOESN'T REMEMBER IF HE INADVERTENTLY HIT THE ELECTRIC FEATHER SWITCH WHEN HE MEANT TO ARM THE AUTOFEATHER SWITCH; OR IF HE HIT THE ELECTRIC FEATHER SWITCH IN RESPONSE TO THE AUTOFEATHER OCCURRING. THE ELECTRIC FEATHER SWITCH IS RIGHT ABOVE THE AUTOFEATHER ARM SWITCH AND IS POORLY GUARDED. THE GUARD FLICKS UP VERY EASILY AND THE SWITCH IS NOT 'OPPOSITE' THE GUARD COVER. ALSO; THERE IS NOTHING IN THE QRH ABOUT DEALING WITH AN INADVERTENT AUTOFEATHER. WHETHER THE ACFT AUTOFEATHERED INADVERTENTLY WHEN THE SWITCH WAS TURNED TO 'ARMED' AND THE ELECTRIC FEATHER SWITCH WAS TURNED ON AS A RESPONSE TO THAT; OR THE 'ELECTRIC FEATHER' SWITCH WAS TURNED ON INADVERTENTLY INITIALLY; THE CAPT CAN'T REMEMBER.