AN MDS80 CAPT RPTED THAT THE GEAR MALFUNCTIONED ON APCH TO DULLES.

Narrative

LOWERED GEAR HANDLE WHEN ON LOC. GEAR INDICATIONS WERE NOSE AND R MAIN NORMAL; L GEAR RED; UNSAFE. ADVISED TWR AS WE APCHED; INBOUND; OF UNSAFE CONDITION AND A POSSIBLE GAR. THE FO WORKED THE CHKLIST FOR UNSAFE GEAR WITH THE HANDLE DOWN WITH NO POSITIVE OUTCOME. WE WENT AROUND; DECLARED AN EMER; AND STARTED WITH DISPATCH. WE WERE GIVEN DELAY VECTORS FROM DULLES APCH AND A RWY CHANGE TO RWY 1R. AFTER EXHAUSTING THE CHKLIST; THE FO WENT BACK TO CHK THE DOWNLOCKS ON THE MAIN GEAR. BOTH DOWNLOCKS INDICATED DOWN AND LOCKED. WE ADVISED TUL TECHNICIAN OF THE STATUS. THEY SAID IF THE DOWNLOCKS INDICATED LOCKED; IT WAS PROBABLY A SENSOR. BOTH LOCKS WERE GOOD. AS A PRECAUTION; WE HAD THE FLT ATTENDANTS PREPARE THE CABIN FOR AN EMER LNDG AND ADVISED THEM WE WOULD BE GIVING THEM A BRACE CALL AS A PRECAUTION. DULLES OPS WAS ADVISED THAT WE WOULD NEED TO PIN THE GEAR ON THE RWY AS A PRECAUTION; AND WE ADVISED DULLES TWR WE WOULD BE CLOSING THE RWY AND PINNING THE GEAR BEFORE TAXIING IN. WE CAME TO A STOP; STRAIGHT ON RWY 1R; CALM WINDS; ROLLING SMOOTHLY TO A STOP NEAR THE DEP END AND STOPPED. A PA WAS MADE FOR THE PAX AND FLT ATTENDANTS TO REMAIN IN THEIR SEATS. MAINT CAME OUT; PINNED THE GEAR. WE HAD THE FIRE TRUCKS FOLLOW US TO THE GATE AS A PRECAUTION. NO FURTHER INCIDENT. L MAIN LIGHT REMAINED RED AND THE RED WARNING HORN STARTED AS WE PARKED AT THE GATE.