E120 FLC RECEIVED A L MAIN LNDG GEAR UNSAFE LIGHT WHEN GEAR WAS SELECTED FOR LNDG. AFTER TWR VERIFICATION OF GEAR EXTENSION AND DISCUSSION WITH MAINT; THE FLC DECLARED AN EMER AND LANDED. THE UNSAFE INDICATION CONTINUED AFTER LNDG.

Narrative

WHEN I SELECTED LNDG GEAR DOWN; THE L MAIN LNDG GEAR INDICATED UNSAFE. THE R MAIN AND NOSE GEAR INDICATED SAFE. WE CYCLED THE LNDG GEAR 3 TIMES. THE INDICATION REMAINED THE SAME. WE CONTINUED THE APCH DOWN TO ABOUT 1200 FT MSL AND FLEW DOWN THE RWY SO TWR COULD CHK THE LNDG GEAR. THE TWR INDICATED IT APPEARED DOWN. WE TURNED OUT FOR AN EXTENDED DOWNWIND AND TALKED TO MAINT. THEY INDICATED WE SHOULD HAVE THE EQUIP ROLLED OUT AND LAND. WE THEN PROCEEDED TO DECLARE AN EMER AND LAND; WITH A NORMAL APCH AND LNDG. THE LNDG GEAR STILL INDICATED UNSAFE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE L MAIN GEAR WOULD NOT LOCK BECAUSE ICE HAD FORMED IN THE LOCKING MECHANISM; BLOCKING IT FROM FITTING ALL THE WAY INTO PLACE. THE ACFT HAD BEEN TAXIED THROUGH SLUSH WHILE IN BHM; AND AFTER TKOF THE SLUSH HAD TURNED TO ICE AND REMAINED FROZEN THROUGHOUT THE FLT AND LNDG AND UNTIL MAINT REMOVED IT IN CVG. THE GEAR WAS STILL HELD IN THE DOWN POS BY HYD PRESSURE; BUT IT WAS NOT OVERCTR. THE INDICATION THAT THE FLC RECEIVED WAS RELATED TO THE PAIR OF MAGNETIC PROX SWITCHES WHICH MUST BE LINED UP TO CLOSE A CIRCUIT. WHEN THE CIRCUIT CLOSES; THE GREEN GEAR LIGHT WILL ILLUMINATE IN THE COCKPIT. THERE WERE ENOUGH PROBS IN THE PAST WITH PROX SWITCHES THAT THE RPTR ASSUMED PROX SWITCHES WERE THE PROB. IN THE FUTURE; HE WILL NOT BUY INTO AN ASSUMPTION. HE WILL STOP THE ACFT AFTER LNDG; HAVE THE GEAR PINS INSTALLED; AND THEN HAVE THE ACFT TOWED TO THE GATE.