Narrative:

I was the PF. We had just been given a lower altitude and a heading by ATC to descend to 7000 ft. I called for the descent check per our company's SOP. The PNF (captain) began his 'descent check 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 left. The captain grabbed the controls, and after a few seconds said, 'I think we just had an inadvertent autofeather.' we informed ATC of our problem and decided to hold on the localizer while we tried to determine what happened. While I was reading the checklists (I was now the PNF), I noticed that the electric feather switch on the left engine was on, and I asked the captain if he had turned it on. He said he didn't remember turning it on, but that he must have. The aircraft was very ctlable and the captain elected not to shut the engine down because it was giving us bleed air and hydraulics and not to declare an emergency because the aircraft was flying fine. The engine was not brought out of feather because it appeared to overtorque. We landed uneventfully. In speaking with the captain 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 aircraft 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 captain can't remember.

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Original NASA ASRS Text

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

Narrative: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.