INFLT ICE FOREIGN OBJECT DAMAGE TO BOTH ENGS.

Narrative

WE WERE ON TOP AT 28000 FT BUT NO REAL CLR HORIZON. OCCASIONALLY WE DID ENTER CLOUDS AT WHICH TIME ENG ANTI- ICE (AI) WAS TURNED ON. IT WAS VERY DARK; ONLY THE STARS AND RADAR WOULD TELL US WHEN WE WERE IN THE CLOUDS. SLIGHT DEVS WERE REQUIRED BUT NOT ENOUGH TO PULL US OFF THE AIRWAY. WHEN WE WERE OUT OF THE CLOUDS ENG ANTI-ICE WAS TURNED OFF. AT NO TIME WAS THERE ANY INDICATION OF ICING. WE WERE EXPERIENCING MODERATE TURB OFF AND ON IN BOTH IMC AND VMC CONDITIONS. AT ABOUT 1 1/2 HRS INTO THE FLT. WE AGAIN APPLIED ENG ANTI-ICE. WE STARTED RECEIVING ST ELMO'S FIRE. I NOTICED ICE ON WINDSHIELD AND AIRFOIL AIRBORNE INTERCEPTION WAS APPLIED. TUBE HAD 3/4 TO 1 INCH AND MY WINDOW WAS ICING UP VERY BADLY. WE EXITED THE CLOUDS APPROX 7-8 MIN AFTER ENTERING. BOTH ENG AND AIRFOIL AIRBORNE INTERCEPTION WERE UTILIZED UNTIL ALL VISIBLE ICE HAD DISSIPATED. ALL ENG INDICATIONS WERE NORMAL DURING APPLICATION AND TERMINATION OF ANTI-ICE SYS. WITHIN 2 MIN AFTER ENG ANTI-ICE AND AIRFOIL WERE APPLIED; WE GOT A CALL FROM THE FLT ATTENDANTS. THEY HEARD 2 LOUD POPS IN BOTH ENGS. I WENT BACK TO INVESTIGATE BUT BOTH ENGS SOUNDED NORMAL. UPON ARR SFO; CAPT AND FO MET WITH 2 COMPANY MAINT PERSONNEL. WE INFORMED THEM OF THE ENCOUNTER. IT WAS OBSERVED THAT A FAN TIP BLADE WAS BENT ON THE L ENG. WE TOLD MECHS WE WOULD WRITE IT UP IN MAINT LOG BUT MECHS SAID THEY WOULD DO IT THE NEXT DAY. CAPT GOT A CALL FROM CHIEF PLT THAT THERE WAS DAMAGE TO BOTH ENGS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR DOES NOT KNOW WHERE THE ICE CAME FROM AND CONCEDES THAT IT MAY HAVE COME FROM THE TOP OF THE WING AND SUPERCOOLED FUEL. THE RPTR 'HAS NEVER SEEN ICE BUILD UP THAT FAST.' THE RPTR ACKNOWLEDGES THAT THE FLC SHOULD HAVE WRITTEN UP THE ENG DAMAGE; BUT IT WAS PRESENTED TO THE FLC AS BEING MINOR TO 1 ENG ONLY. THE CHIEF PLT WAS RATHER GENTLE IN HIS CONVERSION THE NEXT DAY.