DHC8 PIC ASSUMES PXT CTLR ADVISORY AS CLRNC TO NEXT HOLDING FIX; COMING INTO CONFLICT WITH SAME ALT TFC AT 6000 FT AND ALSO WITH TFC AT 5000 FT.

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WE (ACFT X) DEPARTED FROM PHL ENRTE TO ROA. ON DEP; WE WERE ADVISED THAT ZDC COMPUTER WAS DOWN AND WERE RTED APCH CTL TO APCH CTL FROM PHL APCH; TO PXT APCH; TO RIC APCH; TO ROA APCH AT 6000 FT ALT. WHEN WE CONTACTED PXT APCH; WE WERE ADVISED THAT RIC APCH WAS ACCEPTING ENRTE TFC BUT WAS NOT ACCEPTING LNDG TFC. AS WE PASSED PXT; RIC STARTED ACCEPTING LNDG TFC IF THEY CANCELED IFR AT HPN FOR A VISUAL APCH. I THOUGHT THAT ALL HOLDING TFC HAD BEEN CLRED ON TO HPN. WHEN XING COLIN INTXN ON V16 AT 6000 FT ALT; I SAW AN ACFT (ACFT Y) IN A R TURN 4 NM IN FRONT OF US TURNING TO A CO-ALT; HEAD-ON COURSE. AT 2 NM SEPARATION; I STARTED A R TURN TO AVOID THE ACFT. AS I STARTED THE TURN; PXT CTL GAVE US A DSCNT TO 5000 FT AND THE TCASII GAVE AN RA WARNING TO CLB. I STARTED THE DSCNT AND PASSED APPROX 500-700 FT BELOW THE OTHER ACFT. PXT CTL ISSUED A R TURN TO A HDG OF 290 DEGS DURING THE DSCNT. AFTER LEVELING AT 5000 FT; WE SAW ANOTHER ACFT (ACFT Z) XING R TO L 2 NM IN FRONT OF US; CO-ALT. WE TURNED SLIGHTLY R AND PASSED APPROX 1 - 1 1/2 NM BEHIND THE ACFT. AT 6 NM FROM COLIN INTXN; PXT CTL GAVE US A CLRNC TO HOLD AS PUBLISHED AT COLIN. I TURNED L TO GO BACK TO COLIN INTXN AS THE FO LOOKED UP THE HOLDING PATTERN. THERE WAS NO PUBLISHED PATTERN ON OUR CHART. WE QUESTIONED PXT ON THIS AND THEY AGAIN TOLD US TO HOLD AS PUBLISHED. ON THE THIRD QUESTION ON THE HOLDING INSTRUCTIONS; THEY GAVE US DIRECTIONS TO HOLD ON THE INBOUND; SW AT 5000 FT; 1 MIN LEGS. ON THE FIRST OUTBOUND LEG; PXT GAVE US A CLRNC TO GO DIRECT GVE; CLB BACK TO 6000 FT AND HANDED US OFF TO RIC APCH. RIC APCH ADVISED US THAT THEY HAD A COMPUTER FAILURE AND RTED US THROUGH THEIR AIRSPACE AND ON TO ROA APCH. OUR ACFT WAS EQUIPPED WITH A KNS660 FLT MGMNT AND TCASII SYS WHICH WERE A GREAT AID IN SORTING OUT THIS SIT AND MAINTAINING SEPARATION.