A B727-100QF IN CRUISE AT FL330 INADVERTENTLY HAD ENGS #1 AND #3 OPERATING ON SUCTION FEED. RAN PROC TO RESTORE BOOSTED FEED AND NOTED ERRATIC ENG PRESSURE RATIO AND FUEL FLOW INDICATIONS FOR SEVERAL SECONDS.

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AT CRUISE ALT; WE FOUND OURSELVES MISTAKENLY ON A SUCTION FEED OP OF ENGS #1 AND #3. NORMALLY THIS IS NOT A PROB ON A B727; HOWEVER; THE PARTICULAR MODEL B727 WE OPERATE; THIS CAN POTENTIALLY CAUSE A FLAMEOUT. THIS PROB IS KNOWN TO THE OPERATOR AND WE HAVE INTERIM OPERATING PROCS UNTIL A PERMANENT FIX IS APPROVED. WE ELECTED TO RUN A PROC IN OUR CHKLISTS IN ORDER TO RESTORE BOOSTED FUEL PRESSURE. AS WE WERE RUNNING THIS CHKLIST WHICH INCLUDES IDLING BACK EACH ENG ONE AT A TIME IN ORDER TO RESTORE BOOST PUMPS; WE DID NOTICE SOME ERRATIC EPR AND FUEL FLOW INDICATIONS FOR SEVERAL SECONDS; AND THEN NORMAL OP TOOK PLACE FOR REMAINDER OF THE FLT AND DSCNT AND LNDG UNEVENTFULLY. THROUGHOUT RUNNING THIS PROC NORMAL RPM WAS MAINTAINED AS WELL AS NORMAL GENERATOR AND PRESSURIZATION LOADS ON ALL ENGS. ALTHOUGH I THOUGHT THIS EVENT DID NOT MEET ANY REQUIRED RPTING TO VARIOUS AGENCIES; SINCE THIS IS A KNOWN PROB; I WILL STATE THAT ONCE SUCTION FEED EXISTS; IT IS IMPERATIVE TO QUICKLY RESTORE BOOSTED FUEL PRESSURE ASAP TO PREVENT A POTENTIAL ENG FLAMEOUT CONDITION! CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ACFT WAS A B727-100QF EQUIPPED WITH ROLLS ROYCE TAY 651 ENGS. THE RPTR SAID A PROB WITH THIS ENG HAS OCCURRED SEVERAL TIMES AND RESULTED IN ENG FLAMEOUT. THE RPTR SAID THIS ENG WILL NOT SUCTION FEED FUEL USING ONLY THE ENG DRIVEN FUEL PUMP. THE RPTR SAID AN INTERIM PROC HAS BEEN IMPLEMENTED TO AVOID THIS PROB. THE RPTR STATED IN THIS INCIDENT ALL 3 ENGS REMAINED OPERATING BUT DID NOTICE ERRATIC EPR AND FUEL FLOW INDICATIONS.