A WDB PLT STRUCK THE TAIL SKID ON LNDG. THE AUTOTHROTTLES ALLOWED THE ACFT TO GET A LITTLE SLOW.

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THE APCH AND LNDG SEEMED NORMAL EXCEPT THAT THE AUTOTHROTTLE SYS ALLOWED THE AIRSPD TO DECAY BY 5 KTS DURING THE PERIOD FROM 100 FT AGL TO 30 FT AGL. VREF WAS 135 KTS. THE COMMAND AIRSPD BUG (FOR AUTOTHROTTLES) WAS SET TO VREF PLUS 5 AS PER SOP. AT 300 FT AGL; AIRSPD WAS STEADY AT COMMAND BUG PLUS 5 KTS. AT 200 FT IT REMAINED COMMAND BUG PLUS 5 KTS. AT 100 FT IT WAS ON COMMAND BUG. THE FO LATER STATED THAT AS HE WAS STARTING TO MAKE RADIO ALTIMETER CALL OUTS. HE NOTED THE AIRSPD DECREASES. AT 30 FT AGL HE CALLED 'BUG MINUS 5.' I DISCONNECTED THE AUTOTHROTTLES TO PREVENT ANY FURTHER THROTTLE REDUCTION. AS THE FLARE MANEUVER HAD ALREADY BEGUN; A FURTHER DESTABILIZING ACTION WOULD HAVE OCCURRED WITH ANY LARGE THROTTLE CORRECTION. A GAR; AT THIS ALT; WOULD ALSO HAVE BEEN INAPPROPRIATE. I ELECTED TO LAND WITH MIN FLARE AND HOLD OFF. THE ACFT WAS ALLOWED TO SETTLE IMMEDIATELY TO THE RWY. THE LNDG WAS POSITIVE; BUT NOT EVEN FIRM. ROLLOUT WAS UNEVENTFUL. A FLT ATTENDANT LATER RPTED A 'SCRAPING' SOUND ON LNDG. THE FO AND I DID A POST-LNDG WALKAROUND AND FOUND THE TAILSKID DAMAGED. THIS COMPANY HAS HAD NUMEROUS TAILSKID STRIKES ON THE WDB. I RECENTLY CHANGED MY PRACTICE OF SETTING THE COMMAND BUG TO VREF PLUS 10 TO COMPLY WITH THE COMPANY SOP (VREF PLUS 5). THE COMPANY PROC I BELIEVE REFLECTS THE MANUFACTURER'S RECOMMENDATIONS. I SUGGEST THAT VREF PLUS 10 KTS IS A BETTER SPD PRACTICE SUBSTANTIATED BY LINE EXPERIENCE. IT GIVES SLIGHTLY INCREASED MARGINS FOR ERRORS ANY AUTOTHROTTLE LAG.