CAPT OF AN MLG LANDED SHORT OF THE DISPLACED THRESHOLD.

Narrative

ACR ACFT THAT I WAS FLYING TOUCHED DOWN JUST PRIOR TO DISPLACED THRESHOLD ON RWY 31C AT CHICAGO (MDW) ON DATE/TIME INDICATED ABOVE. SURFACE WIND BEING RPTED AS 100/08 OR SLIGHT QUARTERING TAILWIND. ALL THE WAY DOWN THE ILS WE EXPERIENCED A SIGNIFICANT TAILWIND REQUIRING N1 SETTINGS 6-8 PERCENT BELOW NORMAL. I FLEW A COUPLED ILS TO APPROX 150-200 FT AGL AT WHICH TIME I TURNED OFF AUTOPLT AND ASSUMED THE VASI FOR VISUAL REF. AT 100 FT I WAS PRECISELY ON GS ACCORDING TO THE VASI. AT APPROX 30 FT TO 50 FT AGL I REDUCED THE PWR TO IDLE AS WITH ALL NORMAL APCHS FOR THIS MODEL DC9. HOWEVER; THE TAILWIND APPARENTLY DISPATCHED IN THE ROUNDOUT/FLARE CAUSING A SINK RATE RESULTING IN EARLY TOUCHDOWN; PERHAPS AS MUCH AS 1/2 TO 1 ACFT LENGTHS PRIOR TO STRIPE. CONTRIBUTING FACTORS: INFAMOUS SHORT RWY WITH OBSTRUCTIONS. TAILWIND ALL THE WAY DOWN FINAL INCREASING ONE'S DESIRE TO HAVE ACFT TOUCH DOWN TIMELY RATHER THAN FLOAT. VASI LIGHTS FLY YOU EXACTLY TO THE DISPLACED THRESHOLD STRIPE. LOSS OF TAILWIND AS ACFT DSNDS BELOW BUILDING HT (75 FT).