AN ACFT EQUIP PROB ANTI-SKID LOCKUP CAUSED A TFC PROB.

Narrative

AFTER A NORMAL LNDG IN VFR CONDITIONS; DRY RWY; THE CAPT WAS APPLYING BRAKES AS ACFT SLOWED THROUGH ABOUT 90 KTS AT A POINT APPROX 4000 FT DOWN RWY. THERE WAS TFC ABOUT 3 1/2 MI OUT ON FINAL AND PIT TWR CLRED A JETSTREAM 31 COMMUTER ACFT INTO POS AND HOLD IN ANTICIPATION OF ALLOWING A TKOF AS WE EXITED THE RWY. AS ACFT SLOWED BELOW 60 KTS (RAPIDLY SLOWING); THE CAPT TURNED THE ACFT L TOWARD A REVERSE HIGH-SPD TURN OFF TO EXIT THE RWY. AT APPROX 20 KTS AND AFTER 45-50 FT OF TURNOFF; THE ACFT SLID STRAIGHT AHEAD TOWARD THE TXWY EDGE AND STOPPED WITH THE R WING OVERHANGING THE RWY. THE ANTI-SKID HAD LOCKED BOTH L MAIN WHEELS; SKIDDING THE ACFT. THE CAPT STOPPED STEERING INPUT VIA NOSEWHEEL AND STOPPED THE ACFT TO ANALYZE THE SIT. I IMMEDIATELY ADVISED ATC THAT WE HAD NOT CLRED THE RWY. ATC CANCELED THE TKOF CLRNC FOR THE COMMUTER AND SENT THE JET ON FINAL AROUND. I BELIEVE THERE WAS NO CONFLICT OR LOSS OF NORMAL SEPARATION. THIS WAS A MECHANICAL FAILURE AT AN UNEXPECTED TIME AND IN AN UNUSUAL MANNER; AS EVIDENCED BY THE SLOW SPD INVOLVED AND THE RARITY OF OCCURRENCE. AS FOR CORRECTIVE ACTION; ATC SHOULD NOT SO AGGRESSIVELY MOVE TFC ONTO THE RWY AND FINAL APCH PATH WITHOUT BEING CERTAIN THE LNDG TFC HAD INDEED CLRED THE RWY. I COULD ALSO HAVE ADVISED ATC MORE QUICKLY; ALTHOUGH FEW MOMENTS HAD ELAPSED.