Narrative:

En route from mia to lax nearly abeam mob, we requested climb to FL390 from FL350 to minimize effects of thunderstorm line penetration. Aircraft climbed to FL387 then leveled off. Shortly thereafter, airspeed decay occurred and we noted erratic EPR indications and disingenuous comparative engine instrument indications -- throttles remained aligned. Thrust appeared inadequate to maintain altitude so with clearance we descended to FL350. Leveling off there, all left engine indications showed high thrust while right engine EPR was pegged at maximum, yet other parameters showed reduced thrust. No EICAS alerts of any kind ever appeared. Aircraft speed was less than normal for FL350 and would not increase. Maintenance was consulted via phone patch along with dispatch, given our readings and determined an EPR problem was limiting normal thrust on right engine. Suggested matching all instruments disregarding EPR, that resulted in 4 inch throttle misalignment. Determination was made to land at dfw 200 mi ahead en route for mechanical inspection. During descent and within a period of time, engines eventually returned to normal and worked that way throughout the remaining descent, approach and landing. Dispatch was notified of the diversion. Crew did not declare an emergency, however, ATC (ZFW) declared emergency for us in giving us expedited clearance to dfw.

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Original NASA ASRS Text

Title: A B757-200, UNABLE TO MAINTAIN FL390 WITH A FAULTY EPR SENSOR, HAS TO DSND TO FL350 AND THEN DIVERT TO DFW, TX.

Narrative: ENRTE FROM MIA TO LAX NEARLY ABEAM MOB, WE REQUESTED CLB TO FL390 FROM FL350 TO MINIMIZE EFFECTS OF TSTM LINE PENETRATION. ACFT CLBED TO FL387 THEN LEVELED OFF. SHORTLY THEREAFTER, AIRSPD DECAY OCCURRED AND WE NOTED ERRATIC EPR INDICATIONS AND DISINGENUOUS COMPARATIVE ENG INST INDICATIONS -- THROTTLES REMAINED ALIGNED. THRUST APPEARED INADEQUATE TO MAINTAIN ALT SO WITH CLRNC WE DSNDED TO FL350. LEVELING OFF THERE, ALL L ENG INDICATIONS SHOWED HIGH THRUST WHILE R ENG EPR WAS PEGGED AT MAX, YET OTHER PARAMETERS SHOWED REDUCED THRUST. NO EICAS ALERTS OF ANY KIND EVER APPEARED. ACFT SPD WAS LESS THAN NORMAL FOR FL350 AND WOULD NOT INCREASE. MAINT WAS CONSULTED VIA PHONE PATCH ALONG WITH DISPATCH, GIVEN OUR READINGS AND DETERMINED AN EPR PROB WAS LIMITING NORMAL THRUST ON R ENG. SUGGESTED MATCHING ALL INSTS DISREGARDING EPR, THAT RESULTED IN 4 INCH THROTTLE MISALIGNMENT. DETERMINATION WAS MADE TO LAND AT DFW 200 MI AHEAD ENRTE FOR MECHANICAL INSPECTION. DURING DSCNT AND WITHIN A PERIOD OF TIME, ENGS EVENTUALLY RETURNED TO NORMAL AND WORKED THAT WAY THROUGHOUT THE REMAINING DSCNT, APCH AND LNDG. DISPATCH WAS NOTIFIED OF THE DIVERSION. CREW DID NOT DECLARE AN EMER, HOWEVER, ATC (ZFW) DECLARED EMER FOR US IN GIVING US EXPEDITED CLRNC TO DFW.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.