FLC OF AN LTT TURBO PROP EXPERIENCED AND ENG AUTO- FEATHER WHEN THEY REDUCED THE PWR ON 1 ENG IN AN ATTEMPT TO OPEN THE ANTI-ICE BLEED VALVE.

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ON CLBOUT; IN IMC; ACFT ENTERED ICING CONDITIONS. AS I REACHED UP AND TURNED ON ENG ANTI-ICE; WE RECEIVED A MASTER CAUTION INDICATING FAILURE OF THE ANTI-ICE BLEED VALVE TO OPEN ON THE L ENG. CHKLIST CALLS FOR CYCLING THE ANTI-ICE SWITCH AND IF NO SUCCESS; TO LEAVE ICING CONDITIONS. IT ALSO RECOMMENDS REDUCING NG TO BELOW 90 PERCENT TO FORCE BLEED VALVE OPEN; AFTER WHICH NORMAL PWR CAN BE REAPPLIED. I DID REDUCE PWR ON THE L ENG SLOWLY AND EXPLAINED MY ACTIONS TO THE FO WHO SEEMED DISTRACTED BY THE INCIDENT. SUDDENLY; THE ENG LOST THRUST; THERE WAS MOMENTARY CONFUSION AS TO WHAT HAPPENED BUT UPON EXAMINING ENG GAUGES; I CONCLUDED WE LOST THE L ENG; BUT SOMETHING DID NOT MAKE SENSE BECAUSE THERE WAS STILL NORMAL ENG PARAMETERS FOR THE SELECTED PWR LEVER POS; JUST NO OR NEGLIGIBLE TORQUE INDICATIONS. I PLACED THE PWR LEVER BACK UP TO MATCH THE OTHER LEVER AND IN MOMENTS WE HAD BOTH ENGS RUNNING NORMALLY (AND THE ANTI-ICE VALVE FUNCTIONING OK). SINCE THIS WAS THE FIRST REVENUE FLT OF THE ACFT SINCE A NEW L ENG WAS INSTALLED; I THOUGHT THAT WE MAY HAVE A RIGGING PROB. HOWEVER; AFTER THINKING ABOUT WHAT HAPPENED FOR A FEW MINS THE ANSWER OCCURRED TO ME. I ASKED THE FO IF HE TURNED OFF THE AUTO-COARSEN (AUTO- FEATHER) SWITCH AND HE ADMITTED THAT HE FORGOT IT WHEN THE MASTER CAUTION DISTRACTED HIM. SINCE THE COMPUTER SENSED A LARGE DIFFERENCE IN TORQUE BTWN THE ENGS; IT ASSUMED A FAILURE AND FEATHERED THE WEAKER ENG. THE AIRPLANE WAS WORKING NORMALLY (EXCEPT FOR THE ANTI-ICE); THE FEATHERING WAS CREW INDUCED. SEVERAL PROB AREAS THAT NEED TO BE ADDRESSED. FIRST; OUR COMPANY'S CLB CHKLIST IS CALL AND RESPONSE FOR THE FIRST 5 ITEMS ONLY. THE REST OF THE CHKLIST IS DONE SILENTLY. THE FO IS SUPPOSED TO HAVE A 'FLOW' IE; DO ALL REQUIRED ITEMS AND THEN VERIFY WITH A CHKLIST; UNFORTUNATELY; THEY ARE NOT TAUGHT FLOWS ALL OF THE TIME SO SOME DO THE CHKLIST RIGHT; SOME USE IT AS A 'DO-LIST.' ALSO THE ABNORMAL PROC SHOULD SPECIFY AUTO- COARSEN SWITCH-OFF. FINALLY; AND MOST IMPORTANTLY; BOTH MYSELF AND THE FO WERE FINISHING OFF A MONTH IN WHICH WE EACH HAD NEARLY 100 HRS OF FLT TIME. JUDGING BY MY NONCHALANCE TO THE SERIOUS PROB AND MY FO FREEZING UP; I CAN ONLY CONCLUDE THAT WE WERE SERIOUSLY SUFFERING FROM CHRONIC FATIGUE. OUR REACTIONS WERE UNCHARACTERISTIC FOR EITHER OF US AND WE BELIEVE THAT THE ENORMOUS AMOUNT OF WORK WAS FATIGUING US AND ADVERSELY AFFECTING OUR JUDGEMENT.