A B727-200 WITH A RPT OF HIGH EGT ON ALL ENGS WAS RETURNED TO SVC USING THE INCORRECT MAINT MANUAL PROCS.

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ON OCT/XX/97; B727-200 TOOK OFF OUT OF XYZ ON A SCHEDULED FLT TO ZZZ. THE FLC USED A FULL-RATED TKOF PWR ENG SETTING; AS WAS REQUESTED BY MAINT. THE FULL RATED TKOF HAS TO BE ACCOMPLISHED AFTER EACH 'A' CHK. DURING THE TKOF ROLL; THE CREW NOTED THAT ALL 3 ENGS WERE IN THE HIGH EGT (EXHAUST GAS TEMP) RANGE. THE CREW THEN IMMEDIATELY PULLED THE THROTTLES BACK TO A LOWER PWR SETTING AND CONTINUED TKOF. THE FLT CONTINUED UNEVENTFUL AND LANDED IN ZZZ AT ABOUT XA43. MAINT DEBRIEFED THE FLC ON ARR TO ZZZ. THE FLC EXPLAINED TO THE MECH WHAT THEY HAD OBSERVED ON TKOF IN XYZ. WHEN THEY WERE ASKED ABOUT THE EXACT ENG PARAMETERS AND OTHER SPECIFICS TO HELP IDENT THE PROB; THEY WERE UNCERTAIN OF THE PERTINENT DETAILS. BEFORE LEAVING THE ACFT; THE FLC MADE AN ENTRY IN THE ACFT LOGBOOK THAT READ: 'ON FULL PWR TKOF ALL 3 ENGS WENT TO 660 DEGS C TO 670 DEGS C. IMMEDIATELY PULLED PWR BACK TO YELLOW; CONTINUED TKOF.' THE MECH WHO MET THE FLT CONTACTED ME ASKING FOR ASSISTANCE. AFTER I READ THAT CREW RPTED THAT ALL 3 ENGS HAD EXPERIENCED HIGH EGT; I PROCEEDED TO THE MAINT COMPUTER. IN COMPUTER I RESEARCHED FOR ANY PREVIOUS HISTORY ON ACFT ABC PERTAINING TO ENGS. I WAS ABLE TO GO BACK 90 DAYS FROM OCT/XB/97. I DID NOT FIND ANY PREVIOUS RPTS REGARDING EGT OR PERFORMANCE PROBS ON ANY OF THE 3 ENGS. ON THE OTHER HAND; I FOUND 2 PLT RPTS; ONE ON OCT/XC/97 AND THE OTHER ON OCT/XK/97; WHEN A FULL RATED PWR TKOF WAS ACCOMPLISHED AND ALL PARAMETERS WERE NORMAL. KNOWING THAT ALL 3 ENGS HAD NO PREVIOUS HISTORY OF HIGH EGT AND THAT TWO RECENT FULL RATED PWR TKOF WERE ACCOMPLISHED SUCCESSFULLY; I SUSPECTED THAT EITHER THE PLTS MISREAD THE EGT GAUGES OR INLET ANTI-ICE VALVES WERE OPEN DURING TKOF OUT OF XYZ. I DECIDED TO PERFORM A PWR ASSURANCE CHK ON ALL 3 TO VERIFY IF A PROB JUST SUDDENLY AROSE. USING THE APPLICABLE MAINT CHART; A PWR ASSURANCE RUN WAS PERFORMED ON ALL 3 ENGS. THE EGT READINGS ON ALL 3 ENGS WERE WITHIN LIMITS AS DESCRIBED IN THE MAINT MANUAL. I ALSO NOTED THAT THIS ACFT WAS EQUIPPED WITH AN EXPANDED SCALE EGT GAUGE; THIS TYPE GAUGE HAS HASH MARKS IN THE 10 DEG C INCREMENTS. OTHER B727 IN ACR FLEET HAVE NON-EXPANDED SCALE TYPE GAUGES; THIS TYPE HAS HASH MARKS IN 20 DEG C INCREMENTS. THIS INCREASED MY BELIEVE THAT THE CREW MISREAD THE EGT GAUGES. I MADE A JUDGEMENT THAT ALL 3 ENGS WERE SERVICEABLE. I ENTERED AND SIGNED A CORRECTIVE ACTION THAT READ: RAN ALL ENGS AND PERFORMED PWR ASSURANCE CHK AS PER TRIM TABLE IN B727 MAINT MANUAL. ENGS EGT WERE WITHIN LIMITS AS PER CHART. NO PREVIOUS HISTORY. ALL 3 ENGS ARE OK. SUSPECT THAT ENG ANTI-ICE VALVES WERE OPEN. THE SAME DAY; THIS ACFT DEPARTED TO XYZ ON A SCHEDULED FLT. THE NEXT DAY; OCT/XX/97; ACR QUALITY CTL INSPECTOR PERFORMED BOROSCOPE INSPECTIONS ON ALL 3 ENGS AS RECOMMENDED BY MAINT CTL AND PWR PLANT ENGINEERING. THE INSPECTION RESULTS REVEALED THAT #1 AND #2 ENGS HAD NO DEFECTS WHILE #3 ENG FAILED INSPECTION. #3 ENG WAS REPLACED DUE TO INSPECTION FAILURE.