AN ACR MLG GOT CAUGHT IN UNRPTED WIND SHEAR AND MADE A HARD LNDG.

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FLT FROM SLC TO DEN WAS NORMAL THROUGH TURN ONTO FINAL APCH AT DEN RWY 26R. ACFT WAS CONFIGURED NORMALLY WITH NO PROBS. ATIS HAD WIND AT 030 AT 5 KTS. AIR WAS SMOOTH. APCH NORMAL TO 100 FT WITH ONLY SMALL PWR CHANGES REQUIRED TO KEEP STABILIZED ON VASI GS. WITH VVSI STABLE AT ABOUT 800 FPM DSCNT TO 100 FT AGL; AIRSPD THEN BEGAN TO DECAY. APCHING 50 FT; THE AIRSPD APCHED LAST BUG SET AT VREF 40; I CALLED 'AIRSPD.' PWR WAS ALREADY BEING ADVANCED BY THE CAPT. AIRSPD DECAY INCREASED IN RATE BELOW VREF 40; AND VVSI SANK TO 1200 FPM DSCNT. THE CAPT HAD ALREADY APPEARED TO GO TO MAX FORWARD THROTTLE POS; AND ROTATED NOSE FOR GAR WHEN ACFT STRUCK THE RWY TAIL FIRST; FOLLOWED BY MAIN GEAR THEN NOSE GEAR. TWR CALLED AND TOLD US OF SPARKS AND SMOKE ON TOUCHDOWN. I CALLED BACK WITH PIREP OF A LOSS IN AIRSPD OF 25 KTS AT 50 FT; AND ASKED IF ANY FURTHER SMOKE OR FIRE WAS NOTED. TWR STATED THAT THERE WAS NONE. CRASH EQUIP WAS ALREADY ENRTE TO US AS WE TAXIED IN. UP TO THE TIME OF EXCESSIVE AIRSPD DECAY AT 50 FT AGL; THERE WAS NO INDICATION OF ANY SERIOUS WIND SHEAR. NO TWR CALL; NO WIND SHEAR ALERT; NO ATIS; NO PIREP; NO VIRGA NEARBY; NO DUST BLOWING; NO TURB; NO TEMP/DEW POINT SPREAD PROB; NO AIRSPD FLUCTUATION PRIOR TO 50 FT. WE HAD NO MORE THAN 4 SECONDS TO ARREST DSCNT; STOP AIRSPD DECAY; AND GET FULL PWR FROM ENGS. ALL PROCS FOR WIND SHEAR WERE ACCOMPLISHED IN A VERY TIMELY MANNER. SUPPLEMENTAL INFO FROM ACN 240001: AT APPROX 200 FT AGL SLIGHT INCREASE IN AIRSPD NOTICED. AT APPROX 100 FT AGL; EXPERIENCED A LOSS OF 25 KTS; AIRSPD DROPPED. ACFT HIT RWY END EXTREMELY HARD. NO INJURIES; HOWEVER ACFT DID EXPERIENCE SIGNIFICANT STRUCTURAL DAMAGE -- OTS 7 DAYS.