A B757-200 FLC NOTES A LOSS OF AIRSPD AT FL410. THE L ENG PARAMETERS INDICATED AN INFLT SPOOL DOWN. PIC ASKS FOR LOWER ALT FROM ATC AND AFTER 9 MINS THE 'ENG COMES TO LIFE.' DURING EVENT AIRLINE MAINT WAS CONTACTED AND HAD NO SOLUTIONS FOR THE CREW. LATER INFO INDICATED THAT MAINT CTL HAD REF TO A SVC BULLETIN ISSUED FOR THIS SAME ACFT WITHIN THE PAST 2 WKS.

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IN CRUISE AT FL410 I NOTICED A 20 KT DROP IN AIRSPD; LOOKED AT ENG INSTS AND FOUND L HAND EPR GAUGE WELL PAST TOP OF SCALE (TOP IS 2.0 -- IT READ 2.09). ALL OTHER ENG GAUGES READ WHAT APPEARED TO BE IDLE READINGS. THRUST LEVER HAD NOT MOVED. I MOVED THRUST LEVER FORE AND AFT WITH NO CORRESPONDING ENG RESPONSE. AT FIRST RECOGNITION OF PROB WE REQUESTED AND GOT A LOWER ALT. DURING DSCNT WE TURNED ENG ANTI-ICE ON BECAUSE OF VISIBLE MOISTURE. CONFERRED WITH MAINT -- NO SOLUTIONS. APPROX 8-10 MINS AFTER ONSET OF INCIDENT ENG CAME TO LIFE. REST OF FLT UNEVENTFUL. ON GND; MAINT CTL TOLD ME THEY HAVE A SVC BULLETIN ADDRESSING MY EXACT SIT; AND THIS HAD OCCURRED TO THIS ACFT TWICE IN THE PREVIOUS 2 WKS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE ACFT WAS A B757-200 WITH THE ROLLS ROYCE RB-211 ENGS. THE RPTR STATED THAT THIS WAS AN 'INFLT IDLE' SIT EXCEPT THAT THE THROTTLE HAD NOT BEEN AT THE IDLE POS BEFORE THE EVENT; THE THROTTLE HAD NOT BEEN MOVED FROM ITS CRUISE POS. THIS WAS THE 4TH EVENT OF THIS TYPE IN 4 WKS; SAME ACFT; SAME ENG. THE ENG LOSS WAS VERY SUBTLE; WITH NO YAW AND; OF COURSE; NO WARNING ASSOCIATED WITH IT. THE RPTR WAS ANGERED BY THE FACT THAT HE HAD NO PRIOR INFO OF THIS SIT SINCE THE ACR MAINTAINS ONLY THE PREVIOUS DAY'S PAGE FOR THE CREW'S INFO. THE LAST EVENT HAD OCCURRED JUST 2 DAYS BEFORE HIS FLT. THE COMPANY HAD AN OLD MAINT SVC BULLETIN THAT ONLY MAINT HAD ACCESS TO; REFING AN INSTALLATION OF A DRAIN IN THE 'P1' SENSING LINE TO THE FUEL COMPUTER. WHEN THIS PLUG GETS DIRTY IT PLUGS UP. PRIOR TO THE ACR MAINT DEPT 'REMEMBERING' ABOUT THE ISSUANCE OF AN OLD BULLETIN; THE USUAL 'FIX' OR LOGBOOK COMMENT FROM MAINT WOULD BE EITHER A LOGBOOK NOTE THAT THE EPR SENDING UNIT WAS REPLACED; OR 'UNABLE TO DUPLICATE ON THE GND' OR SOME INFO NOTE THAT WAS NOT CARRIED OVER IN THE LOG. MAINT THEN 'REMEMBERED' THE OLD BULLETIN AND AFTER ASSOCIATING THE DRAIN TO THE PROB CLEANED THIS DRAIN AND THAT FIXED THE INFLT IDLE EVENTS. IT WAS; IN ESSENCE; A 'LIQUID TRAP' PROB. THERE IS NO INFLT CHKLIST PROC FOR THIS EVENT. RPTR THOUGHT IT TO BE OF INTEREST THAT IN EACH OF THE 4 CASES; THE CREWS HAD DSNDED AND TURNED ON THEIR ENG ANTI-ICE SYS. AGAIN; IN EVERY CASE; WITHIN 8-9 MINS THE ENG CAME TO LIFE AGAIN. THE COMPANY KNOWS ABOUT THIS; THE PLT'S UNION KNOWS ABOUT IT AND THE RPTR HOPES THAT OTHER OPERATORS OF THE RB-211 AS WELL AS THE MANUFACTURER OF THE ENG KNOWS ABOUT IT. THE PLANE IS FIXED; THE SYS ISN'T. THE DRAIN HAS TO BE KEPT CLEAN.