LNDG GEAR DOOR IS DAMAGED DURING LNDG ROLLOUT.

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ON FINAL APCH I CALLED FOR GEAR DOWN AT 2500 FT AGL. GEAR LOWERED NORMALLY WITH GOOD HYD PRESSURES AND QUANTITIES. MAIN GEAR DOOR LIGHT REMAINED ON; INDICATING A POSSIBLE GEAR DOOR PROB. SUSPECTED A BAD MICROSWITCH; SINCE WE HAD THE LIGHT REMAIN ON FOLLOWING ENG START AND PRIOR TO TAXI BEFORE LAST TKOF. MAINT CONFIRMED DOORS WERE UP AND WERE ABLE TO EXTINGUISH LIGHT. CALLED FOR ABNORMAL CHKLIST WHILE WAITING FOR DOOR LIGHT TO GO OUT. (SOMETIMES IT TAKES SEVERAL SECONDS FOR LIGHT TO EXTINGUISH.) AT 1000 FT AGL LIGHT WAS STILL ILLUMINATED; SO I DIRECTED COPLT TO PULL EMER EXTENSION LEVER WHICH PLACED MAIN GEAR DOORS TO HYD BYPASS. THIS ALLOWED DOORS TO 'FLY' DOWN TO 50 KTS; AT WHICH POINT DOORS CONTACTED RWY SURFACE. DOORS HAVE SKID PLATES DESIGNED TO ABSORB IMPACT FORCES AND PREVENT DAMAGE. LNDG WAS NORMAL AND I ELECTED TO ROLL TO END OF RWY. ADVISED TWR AND THEY SENT LNDG TFC BEHIND US AROUND. TOLD TWR WE WOULD REMAIN AT DEP END OF 9500 FT LONG RWY UNTIL OUR GEAR WAS PINNED AND GEAR DOORS WERE RETRACTED. PROCESS TOOK 35 MINS; DURING WHICH TIME RWY WAS CLOSED. DID NOT DECLARE EMER OR REQUEST PRIORITY HANDLING. FOUND L GEAR DOOR SKID PLATE HAD FAILED DURING LNDG ROLL AND L GEAR DOOR SUSTAINED SHEET METAL DAMAGE. CANCELED OUTBOUND FLT. MAINT PERFORMED SHEET METAL REPAIR AND WE PERFORMED GEAR DOWN MAINT FERRY TO HOME BASE NEXT DAY. ACFT HAD JUST RETURNED FROM 'C' CHK HVY MAINT. PROB DUE TO GEAR DOOR MICROSWITCH OUT OF ADJUSTMENT. WILL RECOMMEND CHANGES TO ABNORMAL CHKLIST TO INCLUDE FACT DOORS WILL LIKELY SUSTAIN SOME DAMAGE. ALSO CONSIDER MINIMIZING LNDG ROLL TO REDUCE TIME DOORS ARE IN CONTACT WITH RWY SURFACE. ADD EXPLANATORY NOTE REGARDING A VISUAL SCAN OF DOORS THROUGH PERISCOPE VIEWER AND PICTURE OF WHAT PROPERLY POSITIONED DOORS LOOK LIKE. ALSO RECOMMEND APCH BE ABANDONED IF PROB NOT CORRECTED BY 1000 FT AGL. PROBABLY RUSHED THINGS TO AVOID GOING AROUND; BUT DID NOT ANTICIPATE ANY DAMAGE TO ACFT. OLD ADAGE 'ONE PEEK IS WORTH 1000 XCHKS' PROVED TRUE DURING THIS INCIDENT.