B727 FLC INITIATE TKOF ABORT ON PHL RWY 9L WHEN OBSERVING ANOTHER ACR TAXIING; WITH NO APPEARANCE OF SLOWING AS THEY APCHED TO CROSS RWY 9L ON TXWY-N; AS THE B727 WAS APPLYING TKOF POWER.

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FLT ABCD WAS CLRED TO TKOF RWY 09L AT PHL. DURING INITIAL PHASE OF TKOF WITH ALL ACFT LIGHTS ON; I NOTICED AN ACR Y ACFT TAXIING N ON TXWY NOVEMBER TOWARD RWY 09L. I DETERMINED THAT IF ACR Y FAILED TO HOLD SHORT; BOTH ACFT WOULD REACH THE INTXN OF RWY 09L AND TXWY NOVEMBER AT ABOUT THE SAME TIME. AT THAT TIME; I ELECTED TO PERFORM A LOW SPEED ABORT. DURING THE ABORT; WE OBSERVED THE ACR Y ACFT CONTINUE N; AND IN FACT; DID NOT SLOW DOWN; BUT TAXIED ONTO THE RWY 09L. FLT ABCD RPTED THAT IT WAS ABORTING DUE TO AN 'ACFT ON THE RWY.' ONCE CLR; IT WAS DETERMINED THAT THE FLT COULD CONTINUE WITHOUT DELAY. ENROUTE TO ATLANTA; THE COMPANY PLT ON DUTY CONTACTED PHL TWR AND THEY RPTED THAT THEY HAD IN FACT EXPERIENCED A BREAKDOWN IN COMMUNICATION. CONTRIBUTING FACTORS: 1) TWR WORKING ACFT ON TWO FREQS. 2) RWY ORIENTATION WITH SETTING SUN XP30 (L) TIME ACR Y CREW WOULD BE LOOKING W INTO THE SUN. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR ASSUMES XING ACR HAD LANDED ON RWY 9R AND WAS EXPEDITING; BY ATC CLRNC AUTHORITY; TO THE RAMP. AS THE RPTR SAW THE SIT DEVELOP; THE PIC WAS WAITING FOR A DC9 TO BECOME AIRBORNE FROM RWY 9L. THE PIC ALLEGES THEY HAD ALREADY BEEN CLRED FOR TKOF; AND THE PIC DIRECTED THE FO TO DELAY TKOF POWER UNTIL THEY COULD SEE THAT THE DC9 WAS AIRBORNE. WHILE DELAYING AND BRINGING UP POWER FOR TKOF; THE AIRBUS CAUGHT HIS EYE; AND PERCEIVED THE AIRBUS WOULD NOT BE ABLE TO STOP IN TIME SHORT OF THE RWY. AS THE BRAKES WERE RELEASED AND NOW UNDER POWER; THE PIC ORDERED THE ABORT. THE AIRBUS ENTERED THE RWY AS THE B727 FO WAS DIRECTED TO ANNOUNCE THE ABORT ON LCL CTL FREQ. THE RPTR STATED THAT PHL TWR FREQUENTLY WILL CLR YOU FOR TKOF WHILE THE PRECEDING ACFT ON TKOF ROLL HAS ALL GEAR YET ON THE RWY SURFACE. THE RPTR BELIEVES THIS TECHNIQUE MAY HAVE CONTRIBUTED TO THIS EVENT IN SOME WAY.