A B747-200 IN CRUISE AT FL390 HAS #3 ENG EPR INCREASE WITH N1; N2; AND EGT DECREASE. 2 SHUTDOWNS AND RESTART NO HELP. DSNDED TO FL350 WITH ANTI-ICE ON AND ENG OP NORMAL. CAUSE UNKNOWN.

Narrative

DURING CRUISE AT FL390 THE #3 ENG EPR BEGAN TO INCREASE RAPIDLY WHILE THE N1; N2; AND EGT WERE DECREASING RAPIDLY. FUEL HEAT WAS APPLIED TO THE ENG WITH NO RESULTS. CONDITION WORSENED. PERFORMED 2 RAPID ENG SHUTDOWN/RESTARTS WITH NO EFFECT. CONTACTED SIN CTL ON HF EXPLAINING PROB AND REQUESTING LOWER ALT. CLRED TO FL350; BEGAN DSCNT; TURNED ON ENG ANTI-ICE. LEVELING OFF AT THE LOWER ALT; THE ENG RESUMED NORMAL OP. PROCEEDED TO DEST WITH NO FURTHER PROB. TOOK ENG SNAPSHOTS AT FL390 AND FL350. WX AT TIME WAS -51 STATIC AIR TEMP; SMOOTH TO MID CHOP; HAZY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED MAINT COULD FIND NO PROBABLE CAUSE FOR THE ENG LOSS OF PWR. THE RPTR SAID THE ENG WAS RUN AT ALL PWR SETTINGS AND NO MALFUNCTION WAS FOUND. THE RPTR SAID THE ENG WAS OPERATED EBOUND AND PERFORMED NORMALLY. THE RPTR STATED THE COMPANY OPERATING MANUAL REQUIRES ANTI-ICE OP AT -40 DEGS STATIC AIR TEMP AND THE AIRPLANE WAS OPERATING AT -51 DEGS. THE RPTR SAID THE ACFT WAS FUELED IN MANILA AND MAY HAVE PICKED UP SOME WATER IN #3 MAIN TANK; BUT THE SAME FUEL WENT IN ALL TANKS.