AN ACR CREW LANDS AFTER THE TWR CLOSED. FLT PLAN IS NOT CLOSED CAUSING DELAYS FOR OTHER ARRIVING ACFT.

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I WAS OPERATING FLT FROM CINCINNATI/NORTHERN KENTUCKY INTL ARPT TO CHARLOTTESVILLE/ALBEMARLE ARPT IN VIRGINIA. I WAS ACTING AS PIC. AT THE TIME I WAS PAIRED UP WITH THE SAME FO FOR THE ENTIRE MONTH. OUR SCHEDULE IS A 'CONTINUOUS DUTY LINE' OR 'HIGH SPD LINE' AS IT IS SOMETIMES REFERRED TO. WE ARE THEN SCHEDULED FOR THE SAME DUTY PERIOD FOR 4 DAYS IN A ROW WITH 2 DAYS OFF INBTWN. THIS SCHEDULE CAN BE FATIGUING AND SLEEP DEPRIVATION CAN SET IN IF SLEEP CANNOT BE ACQUIRED DURING THE DAY. IT DOES HELP IF YOU ARE PAIRED UP WITH THE SAME CREW MEMBERS AND ARE OPERATING TO THE SAME CITY. THE EXTRA SYNERGY AND COMMONALITY OF MISSION AIDS WITH THE LACK OF SLEEP. HOWEVER; COMPLACENCY CAN ALSO BE A FACTOR; AS YOU WILL SOON SEE. WE LEFT CVG BOUND FOR CHO AT XA52 UTC. THE DEP; ENRTE AND ARR WX WERE IFR. LOW CEILINGS EXISTED AT CHO AND THE ILS WAS EXECUTED TO JUST ABOVE MINIMUMS. THE UNUSUAL SIT EXISTS WITH OUR ARR TIME. THE CHO TWR CLOSES AT XC00 EST. DOING THIS FLT ALL MONTH WE HAVE FOUND OURSELVES EARLY MOST OF THE TIME; BUT OUR SCHEDULED ARR TIME IS XC09. SINCE WE ARE ABLE TO MAKE IT IN PRIOR TO THE TWR CLOSING THERE REALLY HAS NEVER BEEN A NEED TO CANCEL OUR IFR CLRNC WHEN WE ARE ON THE GND. THIS PARTICULAR NIGHT WE WERE JUST SLIGHTLY LATE AND THE TWR WAS ADVERTISING ITS CLOSURE. WE WERE TALKING TO WASHINGTON APCH CTL. JUST AFTER BEING CLRED FOR THE APCH; THE CTLR TOLD US WE COULD CANCEL OUR CLRNC IN THE AIR OR ON THE GND. WE OPTED TO CANCEL ON THE GND DUE TO THE LOW CEILINGS. THIS IS ALSO RATHER UNUSUAL IN OUR SYS TO LAND AT AN ARPT THAT HAS TWR CLOSURE AT ALL. WE LANDED WITHOUT INCIDENT AND ODDLY ENOUGH AS WE MADE OUR ANNOUNCEMENT ON THE TWR/CTAF FREQ THAT WE WERE CLR OF THE RWY; THE TWR CTLR STATED THAT THE CTL TWR WAS NOW CLOSED AND MADE THE STANDARD CLOSURE ANNOUNCEMENT. WE HAD NOT HEARD THE CTLR TALK TO US OR MAKE HIM KNOWN AT ALL WHILE WE WERE STATING OUR INTENTIONS DURING THE APCH IN THE BLIND. NO OTHER TFC WAS IN THE AREA AT THE TIME EITHER; SO WE THOUGHT WE WERE BROADCASTING IN THE BLIND. THE CTLR MUST HAVE BEEN THERE BECAUSE HE MADE THE ANNOUNCEMENT AFTER WE CLRED THE RWY. MY FO AND MYSELF THOUGHT THAT WAS ODD AND WE WERE BUSY COMPLETING AFTER LNDG PROCS FOR OUR VERY SHORT TAXI TO THE GATE. EAGERLY WANTING TO GET TO THE HOTEL QUICKLY FOR OUR REST; WE SIMPLY FORGOT OR DID NOT QUESTION ANY FURTHER THE CANCELING OF OUR IFR CLRNC. THIS WAS NEVER NECESSARY SO IT WOULD HAVE BEEN OUT OF SEQUENCE. NOBODY EVER QUESTIONED THE FORGETFULNESS OF NOT CANCELING OUR CLRNC UNTIL A FEW DAYS LATER. SOMEBODY BROUGHT TO OUR ATTN THAT ANOTHER ACR HAD TO CIRCLE FOR AN HR BEFORE THEY COULD LAND. WE SHOULD HAVE CONTACTED APCH CTL TO MAKE THEM AWARE THAT WE WERE ON THE GND SAFE IN CHO. I THINK THAT THERE ARE SAFETY ISSUES THAT NEED TO BE RESOLVED IN REGARDS TO THESE CONTINUOUS DUTY TRIPS. IT IS PERFECTLY LEGAL; BUT IT IS JUST NOT A PERFECT WORLD WHERE THE AVERAGE HUMAN BEING IS ABLE TO GET SLEEP ALL DAY LONG BEFORE A LATE RPT AND THEN GET 4 HRS SLEEP AT A HOTEL BEFORE THE NEXT FLT. I ALSO THINK THAT A CTL TWR SHOULD BE OPEN 24 HRS A DAY AT ARPTS WHERE COMMERCIAL ACFT ARE CARRYING PAX WHO HAVE PAID FOR A SAFE SVC TO THEIR DEST. IF WE DID NEED ASSISTANCE THEN I BELIEVE THERE COULD BE SOME DELAYS IN GETTING THE NECESSARY ASSISTANCE. SINCE THIS SEEMS TO FALL SLIGHTLY OUTSIDE WHAT WE ARE USED TO DOING PROCEDURALLY; IT IS HARD TO REMEMBER AN EASY PROC SUCH AS THIS.