Narrative:

Descending through FL330 the #2 engine over-sped. The aircraft yawed to the left, the engine spooled up, and the autothrottles disengaged. We manually disengaged the autothrottles to get out of thrust lock and pulled the power back to idle, but the RPM remained in redline (N1). We shut down the engine, declared an emergency, called dispatch, and diverted to phl. The thrust lever lost complete control of the engine: thrust lever idle -- engine RPM in redline. Callback conversation with reporter revealed the following information: with autothrottles engaged and commencing a 'managed' descent, the #1 engine went to idle as is normal, but the #2 engine increased RPM. The #2 over-sped as the RPM went to over 100 percent and continued to increase with the N1 gauge pulsing red. The autothrottles automatically disengaged and reporter captain also disconnected them manually. Trying to regain control of the engine with throttle movement was unsuccessful and, with increasing over-speed the flight crew shut down the engine. The destination airport WX was marginal and aircraft was heavy, so flight crew diverted to a closer, more suitable airport. Reporter sent a safety report to his company chief pilot, but as yet had no feedback. However, when flying the same aircraft later, the logbook corrective action included, replacing the eiu (engine interface unit), borescoping the engine and full run-up check.

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Original NASA ASRS Text

Title: ACFT EQUIP PROB. ENG OVER-SPEED UNCONTROLLABLE THROTTLE.

Narrative: DSNDING THROUGH FL330 THE #2 ENG OVER-SPED. THE ACFT YAWED TO THE L, THE ENG SPOOLED UP, AND THE AUTOTHROTTLES DISENGAGED. WE MANUALLY DISENGAGED THE AUTOTHROTTLES TO GET OUT OF THRUST LOCK AND PULLED THE PWR BACK TO IDLE, BUT THE RPM REMAINED IN REDLINE (N1). WE SHUT DOWN THE ENG, DECLARED AN EMER, CALLED DISPATCH, AND DIVERTED TO PHL. THE THRUST LEVER LOST COMPLETE CTL OF THE ENG: THRUST LEVER IDLE -- ENG RPM IN REDLINE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: WITH AUTOTHROTTLES ENGAGED AND COMMENCING A 'MANAGED' DSCNT, THE #1 ENG WENT TO IDLE AS IS NORMAL, BUT THE #2 ENG INCREASED RPM. THE #2 OVER-SPED AS THE RPM WENT TO OVER 100 PERCENT AND CONTINUED TO INCREASE WITH THE N1 GAUGE PULSING RED. THE AUTOTHROTTLES AUTOMATICALLY DISENGAGED AND RPTR CAPT ALSO DISCONNECTED THEM MANUALLY. TRYING TO REGAIN CTL OF THE ENG WITH THROTTLE MOVEMENT WAS UNSUCCESSFUL AND, WITH INCREASING OVER-SPEED THE FLC SHUT DOWN THE ENG. THE DEST ARPT WX WAS MARGINAL AND ACFT WAS HVY, SO FLC DIVERTED TO A CLOSER, MORE SUITABLE ARPT. RPTR SENT A SAFETY RPT TO HIS COMPANY CHIEF PLT, BUT AS YET HAD NO FEEDBACK. HOWEVER, WHEN FLYING THE SAME ACFT LATER, THE LOGBOOK CORRECTIVE ACTION INCLUDED, REPLACING THE EIU (ENG INTERFACE UNIT), BORESCOPING THE ENG AND FULL RUN-UP CHK.

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.