WDB ACR ATTEMPTING TO DO 180 AT END OF RWY AT VOK DRIVES GEAR OFF OF PAVEMENT. NO DAMAGE.

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WHILE ATTEMPTING TO MAKE 180 DEG TURN AT VOK AIR BASE IN WDB. COULD NOT COMPLETE TURN BECAUSE OF ACFT VERY LIGHT WT (400;000 POUNDS); AND BEING AT END OF RWY WHERE RWY'S MARKINGS ARE SLIPPERY. BEING STUCK IN THAT POS WITH NO FACILITIES AT VOK TO MOVE THE ACFT; I UTILIZED REVERSE THRUST TO ATTEMPT TO GET ACFT TO ROLL BACK SLIGHTLY TO ALLOW FOR ANOTHER ATTEMPT. BODY GEAR ROLLED TOO FAR AFT AND DROPPED OFF HARD SURFACE. NO DAMAGE WAS DONE TO ACFT. JUST TO THIS CAPT'S FEELINGS. (EMBARRASSING AT THE LEAST). FACTORS CONTRIBUTING: TAXIWAY AT THE END OF RWY (CLOSED) WHICH WE HAD PLANNED TO USE WAS 'CLOSED' NOT NOTAMED. ADDITIONAL CONSTRUCTION OF AIRFIELD ALSO NOT NOTAMED. WE WERE TOLD TO MAKE L TURN INSTEAD OF R THUS NOT ALLOWING US TO USE WHAT LITTLE BIT OF CONCRETE WAS USABLE AT THE INTXN OF TAXIWAY AND RWY. ACFT VERY LIGHT WT; VERY POOR NOSE WHEEL STEERING AT LIGHT WT; AND SINCE WE WERE NOT ADVISED OF TAXIWAY CLOSED; WE WENT TO END OF RWY TO USE SAME (NOW BTWN ROCK AND HARD SPOT). TOLD TO MAKE R TURN INSTEAD OF L (MORE DIFFICULT FROM L SEAT). PAINTED SURFACES AT END OF RWY SLIPPERY WIND WOULD HAVE PERMITTED DOWNWIND LNDG (LESS THAN 10 KTS) TO E (RWY 9) THAN NO TURNS REQUIRED BECAUSE PARKING WAS AT THE E END. (NEVER OFFERED THIS OPTION). NO TRACTOR AVAILABLE TO MOVE ACFT NEAREST ONE 5 HRS AWAY. MY COMPANY NEEDS TO DO MORE CHKING BY PHONE BEFORE WE OPERATE.