B737-400 ENCOUNTERS DEBRIS FROM FAILED TIRE DURING TKOF ROLL AT ANC.

Narrative

DEPARTING ANC BEHIND A B747 WE CAME VERY CLOSE TO IMPACTING DEBRIS ON THE RWY FROM A TIRE FAILURE ON THE PRECEDING ACFT. THE PRECEDING ACFT (A B747) DEPARTED FROM THE RWY EXTENSION OF RWY 32. WE OBSERVED THE LONG TKOF ROLL OF THE ACFT (55-60 SECONDS FROM BEGINNING OF THE ROLL TO ROTATION) AND TIMED 2 MINS FOR SEPARATION AS WE TAXIED INTO POS FROM THE KILO INTXN. NOTHING ABNORMAL WAS NOTED ON THE DEP OF THE B747. WE COMMENTED THAT IT MUST HAVE BEEN VERY HVY AND THAT WE WOULD BE WELL ABOVE ITS WAKE. 1 MIN 55 SECS AFTER THE BEGINNING OF THE B747'S TKOF ROLL; ANC TWR ISSUED TKOF CLRNC FOR OUR FLT. THE FO WAS FLYING AND COMMENCED THE TKOF ROLL SHORTLY AFTER CLRNC WAS RECEIVED. TKOF ROLL WAS UNEVENTFUL AS WE APCHED V1. I WAS MONITORING SPD THROUGH THE HGS TO MAKE THE APPROPRIATE CALL (V1/VR/V2) TO THE FO. MY EYES WERE FOCUSED AT INFINITY THROUGH THE HGS IN ORDER TO SEE THE SPD DISPLAY AND AS WE APCHED V1; I NOTICED WHAT APPEARED TO BE A BLACK SMUDGE ON THE RWY. IT ACTUALLY APPEARED TO BE JUST AN AREA OF HEAVIER THAN NORMAL RUBBER ON THE PAVEMENT AS IS NORMAL IN THE LNDG ZONES. AS I CALLED V1 AT 5 KTS PRIOR TO V1 (SOP) AND REMOVED MY HAND FROM THE THRUST LEVERS; I REALIZED THAT THE BLACK SMUDGE WAS BEGINNING TO SHOW RELIEF AND WAS ACTUALLY RISING ABOVE THE RWY SURFACE. AT ABOUT THE VR CALL; I DETERMINED THAT THE BLACK SMUDGE WAS A LARGE DEBRIS FIELD FROM A TOTAL TIRE FAILURE PERHAPS 1000-1500 FT IN FRONT OF US. THE FO HAD JUST COMMENCED A NORMAL ROTATION AND I WAS CONCERNED THAT WE MAY IMPACT THE DEBRIS SO I APPLIED A LITTLE EXTRA BACK PRESSURE ON THE YOKE AND COMMENTED THAT I WAS 'COMING ON IT A LITTLE.' WITH A SLIGHTLY HIGHER THAN NORMAL ROTATION RATE; WE BECAME AIRBORNE ABOUT 500-1000 FT PRIOR TO THE DEBRIS. TWR WAS NOTIFIED AS WAS THE PRECEDING ACFT AND THE REST OF THE FLT WAS UNEVENTFUL. AS WE FLEW OVER THE DEBRIS; I NOTED THAT WHAT I HAD INITIALLY SEEN WAS THE ENTIRE OUTER TREAD OF A LARGE ACFT TIRE. THERE WAS ALSO SIGNIFICANT TIRE DEBRIS SCATTERED ALL AROUND THE GENERAL AREA. THE TREAD WAS LYING JUST L OF CTRLINE; INLINE WITH THE L ENG AND MAIN MOUNT TRACK. IMPACT AT HIGH SPD (ROTATION) WOULD HAVE ALMOST CERTAINLY LED TO SEVERE OR CATASTROPHIC DAMAGE TO OUR ACFT. I THINK IF WE HAD ROTATED AT A NORMAL RATE WE STILL WOULD HAVE CLRED THE DEBRIS. I THINK THE HGS AND MY SCAN THROUGH IT FOR V-SPDS GREATLY ASSISTED IN EARLIER RECOGNITION AND BETTER REACTION TIME. THE FO (NO HGS-INSIDE/OUTSIDE SCAN) DID NOT SEE THE DEBRIS UNTIL I BEGAN ASSISTING WITH THE ROTATION. IF IT HAD BEEN NIGHT WE NEVER WOULD HAVE SEEN IT. ANOTHER 2 OR 3 ENG HVY WITH A LONGER TKOF ROLL WOULD HAVE CERTAINLY IMPACTED THE DEBRIS.