Light transport has inadvertent engine feather on descent to land.

Attributes
ACN	276800
Time
Date	199407
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : mzb airport : san
State Reference	CA
Altitude	msl bound lower : 9000 msl bound upper : 9000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : san tower : ord
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other
Flight Phase	cruise other descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 170 flight time total : 3330 flight time type : 100
ASRS Report	276800
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : declared emergency other
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were at our cruise altitude of 9000 ft, just prior to beginning our descent. As the PF, I called for the descent check and we heard a 'bang' and the aircraft yawed left. The autoplt was engaged at the time and I disengaged it and began to hand fly. The captain determined that we had a partial engine failure. When I looked at the instruments, the right engine was normal (63 percent torque, 85 percent np) and the left engine was higher torque (around 100 percent) and np 39 percent. The captain brought the throttle back, then forward, and back again with no apparent effect on controling the engine. The engine was definitely operating, but was apparently feathered. We declared an emergency and were cleared for a visual to runway 27. We continued to fly downwind and performed the precautionary shutdown procedure and reviewed the single engine go around. We then turned into the airport and landed uneventfully. We taxied to the gate, deplaned the passenger and reviewed the events. The autofeather was unarmed and the left engine electric feather switch had been activated. The captain could not remember activating either switch and asked me if I had, which I had not. The switch position could have been selected as part of the precautionary engine shutdown procedure. The captain, however, thinks that he may have accidently activated the electric feather pump instead of arming the autofeather (they are above each other on the overhead panel) when I called for the descent check. I cannot verify that this is what happened, but it is a possibility. However, the electric feather switch is a guarded switch to prevent such an occurrence. If this is the case, knowing that human error is such a significant factor in many incidents and accidents, it is imperative that each of us take more time to insure we're activating the correct switch and continue to improve cockpit designs so as to prevent incidents such as this one.

Original NASA ASRS Text

Title: LTT HAS INADVERTENT ENG FEATHER ON DSCNT TO LAND.

Narrative: WE WERE AT OUR CRUISE ALT OF 9000 FT, JUST PRIOR TO BEGINNING OUR DSCNT. AS THE PF, I CALLED FOR THE DSCNT CHK AND WE HEARD A 'BANG' AND THE ACFT YAWED L. THE AUTOPLT WAS ENGAGED AT THE TIME AND I DISENGAGED IT AND BEGAN TO HAND FLY. THE CAPT DETERMINED THAT WE HAD A PARTIAL ENG FAILURE. WHEN I LOOKED AT THE INSTS, THE R ENG WAS NORMAL (63 PERCENT TORQUE, 85 PERCENT NP) AND THE L ENG WAS HIGHER TORQUE (AROUND 100 PERCENT) AND NP 39 PERCENT. THE CAPT BROUGHT THE THROTTLE BACK, THEN FORWARD, AND BACK AGAIN WITH NO APPARENT EFFECT ON CTLING THE ENG. THE ENG WAS DEFINITELY OPERATING, BUT WAS APPARENTLY FEATHERED. WE DECLARED AN EMER AND WERE CLRED FOR A VISUAL TO RWY 27. WE CONTINUED TO FLY DOWNWIND AND PERFORMED THE PRECAUTIONARY SHUTDOWN PROC AND REVIEWED THE SINGLE ENG GAR. WE THEN TURNED INTO THE ARPT AND LANDED UNEVENTFULLY. WE TAXIED TO THE GATE, DEPLANED THE PAX AND REVIEWED THE EVENTS. THE AUTOFEATHER WAS UNARMED AND THE L ENG ELECTRIC FEATHER SWITCH HAD BEEN ACTIVATED. THE CAPT COULD NOT REMEMBER ACTIVATING EITHER SWITCH AND ASKED ME IF I HAD, WHICH I HAD NOT. THE SWITCH POS COULD HAVE BEEN SELECTED AS PART OF THE PRECAUTIONARY ENG SHUTDOWN PROC. THE CAPT, HOWEVER, THINKS THAT HE MAY HAVE ACCIDENTLY ACTIVATED THE ELECTRIC FEATHER PUMP INSTEAD OF ARMING THE AUTOFEATHER (THEY ARE ABOVE EACH OTHER ON THE OVERHEAD PANEL) WHEN I CALLED FOR THE DSCNT CHK. I CANNOT VERIFY THAT THIS IS WHAT HAPPENED, BUT IT IS A POSSIBILITY. HOWEVER, THE ELECTRIC FEATHER SWITCH IS A GUARDED SWITCH TO PREVENT SUCH AN OCCURRENCE. IF THIS IS THE CASE, KNOWING THAT HUMAN ERROR IS SUCH A SIGNIFICANT FACTOR IN MANY INCIDENTS AND ACCIDENTS, IT IS IMPERATIVE THAT EACH OF US TAKE MORE TIME TO INSURE WE'RE ACTIVATING THE CORRECT SWITCH AND CONTINUE TO IMPROVE COCKPIT DESIGNS SO AS TO PREVENT INCIDENTS SUCH AS THIS ONE.

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.