A SEMI 1 ENG INOP APCH IS FLOWN BY THE CREW OF A B737-700 AFTER KEEPING THE #1 ENG BACK TO IDLE THRUST DUE TO A SUSPECTED INTERNAL FAILURE OF ENG DURING DSCNT AND APCH INTO OAK; CA.

Narrative

AFTER 3.5 HRS OF CRUISE FLT AT FL390; WE EXPERIENCED A SHARP JOLT AND NOTICED THE #1 ENG N1 WAS FLUCTUATING ABOUT 2% THEN ALL INDICATIONS RETURNED TO NORMAL. WE HAD A BRIEF CONVERSATION WITH THE FLT ATTENDANTS AND THEY HAD FELT THE JOLT TOO. THEY CHKED AND RPTED THAT #1 LOOKED NORMAL. WE STARTED DOWN FOR OAK. AT FL280; LEVELING OFF; THERE WAS A PRONOUNCED VIBRATION IN THE AIR FRAME UPON BRINGING UP THE PWR; BUT BOTH VIBRATION METERS READ ABOUT 1. I RETARDED EACH PWR LEVER AND DETERMINED #1 ENG TO BE THE CAUSE. WE OPERATED THE #1 ENG AT IDLE FOR THE REMAINDER OF THE FLT AND NO VIBRATION WAS EVIDENT. #1 WAS RUNNING ABOUT 60 DEGS HOTTER THAN THE #2 AND THE MORNING'S TREND SHOWED THEY WERE ALMOST EVEN IN TEMPS BEFORE. WE STARTED THE APU AND PLANNED FOR A FLAPS 15 DEG APCH AND LNDG. AT CATTY WE ASKED FOR DIRECT THE FIELD AND RELIEF FROM THE HAYWARD RESTR. ON APCH; WE RECEIVED THE 'TOO LOW FLAPS' WARNING WHICH WE INHIBITED AFTER CHKING THE CONFIGN. WE LANDED WITHOUT INCIDENT AND WERE MET BY EMER EQUIP. THEY RPTED NO VISIBLE PROBS. WE SECURED THE ENG AND TAXIED TO THE GATE TO TERMINATE. THE NEXT MORNING MAINT CTL TOLD ME THE #1 ENG COMPRESSOR SECTION HAD STARTED TO SEIZE AND WE WERE LUCKY TO HAVE IT RUN AS LONG AS IT DID. THE ENG WAS BEING CHANGED. SUPPLEMENTAL INFO FROM ACN 591871: UPON REACHING 200 FT AGL; GPWS FLAP ALERT WAS ACTIVATED DUE TO FLAPS 15 DEG LNDG AND I THEN SWITCHED FLAP INHIBITOR SWITCH ON. WE LANDED UNEVENTFULLY WITH MEN AND EQUIP STANDING BY. WE STARTED THE APU IN THE EVENT OF AN ENG FAILURE. AFTER INSPECTION; WE HEARD THE L ENG'S COMPRESSOR BEARING HAD SEIZED AND REDUCING THRUST TO IDLE WAS THE CORRECT ACTION TAKEN.