A320 CAPT HAD A HARD LNDG AT ORD WHILE GETTING IOE TRAINING.

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ORD APCH CLRED US FOR THE APCH TO RWY 9R; MAINTAIN 190 KTS TO DEANA; FOLLOWING A HVY B767. OVER 1 MI OUTSIDE DEANA; WE SELECTED MANAGE SPD AND SLOWED TO APCH SPD. CAPT DISCONNECTED THE AUTOPLT AT ABOUT 800 FT TO STAY SLIGHTLY ABOVE THE GS. OUR APCH WAS NORMAL THROUGH 50 FT AGL WHEN CAPT RETARDED THE THROTTLES TO IDLE THRUST. AT ABOUT 30 FT; THE ACFT STARTED TO SINK RAPIDLY. WE GOT A GPWS SINK RATE WARNING. CAPT ADDED PWR AND WENT AROUND. THE MAIN WHEELS FIRMLY CONTACTED THE RWY DURING THE GAR. AFTER THE MISSED APCH; WE LEVELED AT 4000 FT; CALLED THE CHIEF PURSER TO MAKE SURE EVERYONE WAS ALRIGHT. SHE HAD CHKED WITH THE FLT ATTENDANTS IN THE BACK AND EVERYONE WAS OK. WE RETURNED FOR AN UNEVENTFUL LNDG ON RWY 4R. WE DID CALL FOR THE EQUIP JUST IN CASE THERE WAS ANY GEAR OR TIRE DAMAGE FROM OUR PREVIOUS GAR. WE PULLED INTO THE RWY 27R PAD AND THE EMER CREWS CHKED OUR GEAR AND TIRES. EVERYTHING WAS OK. WE TAXIED TO THE GATE AND SPOKE TO MAINT ABOUT THE HARD LNDG. SUPPLEMENTAL INFO FROM ACN 523793: ABOUT 800 FT; I DISCONNECTED THE AUTOPLT TO STAY SLIGHTLY ABOVE THE GS. AT 50 FT 'HAT' STARTED RETARDING THROTTLES AND ABOUT 30 FT; 'HAT' NOTICED A SUDDEN CHANGE IN SINK RATE. NOTICING THAT WE WERE CAUGHT IN WAKE VORTICES; INITIATED A GAR. THE ACFT TOUCHED DOWN AT A HIGH SINK RATE AS WE ACCELERATED FOR THE GA. I FEEL THAT CLOSELY FOLLOWING TFC PATTERNS AT ORD ARE STARTING TO BECOME TIGHTER AND MORE DANGEROUS. CLOSELY FOLLOWING HVY JETS SHOULD BE AVOIDED.