CONSTANT TORQUE ON TKOF SYSTEM MALFUNCTIONED ALLOWING ENGINE TO OVERTEMP AND OVERSPEED RESULTING IN ENGINE DAMAGE AND CHANGE.

Narrative

ON THE FIRST TKOF FROM WICHITA THE CTOT SWITCHES (CONSTANT TORQUE ON TKOF) WERE ARMED TO FIRE TO PRODUCE THE DESIRED AND SELECTED 95%. THE LEFT ENG ACCELERATED TO 112% AND ENG TEMP WENT TO APPROX 947 DEGS C DIGITAL READOUT. MAX TRANSITIONAL TEMP ALLOWED IS 960 DEGS C AND 118% TORQUE FOR 12 SECS. SINCE MY F/O WAS FLYING I TURNED THE SWITCHES (CTOT) OFF AND PWR BECAME MORE NORMAL. SINCE THIS IS NOT AN UNUSUAL OCCURRENCE (I AND MY FELLOW PLTS HAVE SEEN TORQUE OVERSHOOTS BEFORE WITH SUBSEQUENT TKOFS TOTALLY NORMAL); I MADE A MENTAL NOTE OF IT. ON THE SECOND TKOF WHERE I WAS FLYING; WE SELECTED TARGET TORQUE (ACCORDING TO PWR CHARTS) AND 102% WAS DIALED ON CTOT PANEL. PWR WAS BROUGHT UP SLOWLY CHKING ALL ENG PARAMETERS WHICH WERE NORMAL. AT APPROX 60-70 KTS; I CALLED FOR SWITCHES ON AND AFTER THE USUAL ONE TO ONE AND A HALF SECOND LAG THE CTOT SYS FIRED. ALL SEEMED NORMAL IN PWR ACCELERATION. I HAD TO DIVIDE MY ATTN TO THE RWY; AIRSPD AND PWR QUADRANT. WE HAD A STRONG HEADWIND SO V1 CALL CAME FAIRLY QUICKLY. WHEN I BROUGHT MY EYES BACK TO THE TEMP AND TORQUE GAUGES; BOTH WERE ACCELERATING PAST THE 102% ALREADY SELECTED. I AM IN REF TO THE LEFT ENG ONLY. BY THE TIME I CALLED FOR SWITCHES OFF THE TORQUE; HAD GONE TO 115+% AND TEMP HAD HIT 975 DEGS C DIGITAL. BOTH WERE THERE FOR 2 SECS OR LESS. THIS WAS THE FIRST TIME I HAD WITNESSED AN OVERSHOOT THIS BAD AND ON SUCCESSIVE TKOFS. USUALLY THE SECOND TKOFS WERE NORMAL. A SQUAWK WRITTEN IN 5/88 STATED THAT THE LEFT ENG HAD BEEN STARTING HOT. SEVERAL DAYS OF HOT STARTS WILL DAMAGE AN ENG MORE THAN A 2 SEC OVERTEMP. I WROTE UP MY OWN SQUAWK QUOTING THE TORQUES AND TEMPS LISTED ABOVE. AN ENG BREAKDOWN INDICATED DAMAGE TO THE TURBINE WHEELS AND BLADES. I BELIEVE THIS OCCURRED DUE TO MALFUNCTIONS IN SOME PARTS OF THE CTOT SYS. THE TKOF WAS NOT ABORTED AS WE HAD ALREADY REACHED V1 AND AFTER THE SWITCHES WERE TURNED OFF; ALL OTHER PARAMETERS WERE NORMAL.