LR55 HAS STEERING PROBS ON TKOF ROLL; DEPARTS RWY.

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WE WERE CLRED TO TAXI OUR LEAR 55 TO RWY 35 AT PHL FROM FBO. WE PROCEEDED VIA THE PARALLEL TXWY AND HELD SHORT OF THE RWY. WE RECEIVED TKOF CLRNC AND TAXIED TO THE END OF THE RWY; COMPLETED THE BEFORE TKOF CHKLIST; USED A BRAKE RELEASE TKOF ROLL. PWR WAS SET BY COPLT; AND 'AIRSPD ALIVE' CALLOUT WAS MADE BY THE COPLT. AT THAT TIME; I DISENGAGED STEERING AND THE ACFT VEERED TO THE L. WE EXITED THE RWY APPROX 300 FT FROM THRESHOLD AND I MAINTAINED DIRECTIONAL CTL AFTER; BUT COULD NOT BRING ACFT BACK ONTO RWY. ABORT TKOF PROCS WERE COMPLETED AND THE ACFT CAME TO A STOP APPROX 10-20 FT FROM THE RWY IN A PARALLEL POS. I'M NOT SURE WHETHER IT WAS A STEERING MALFUNCTION; OR RE-ENGAGEMENT; OR BLOWN NOSE TIRE THAT CAUSED THE ACFT TO GO L. THERE WAS NO DAMAGE TO ACFT EXCEPT BLOWN NOSE TIRE AND BENT WHEEL. NO OTHER ACFT WERE INVOLVED IN THE INCIDENT; BUT A B747 LANDED ON A PERPENDICULAR RWY BEFORE WE INITIATED TKOF ROLL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES MAINT WAS UNABLE TO FIND ANY STEERING PROB. THEY ARE NOW CHKING TO SEE IF THE NOSEWHEEL MIGHT HAVE GONE FLAT PRIOR TO TKOF AND THE WHEEL CASTERED. RPTR INDICATED HE WOULD CALL BACK WITH INFO WHEN SOMETHING IS DETERMINED.