BE1900 CREW LOST ACFT CTL AFTER LNDG ON RWY 35 AT GCK.

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WE DEPARTED ZZZ ENRTE TO GARDEN CITY; KS. THE FO WAS THE PF AND THE CAPT WAS THE PNF. DEADHEADING ON THAT FLT WITH US WAS MR X; AN ACR Y CAPT. THE CAPT HAD PICKED UP THE WX FOR GCK AND BRIEFED THE WX TO ME. AT THE TIME THE ARPT WAS RPTING VFR CONDITIONS AND LIGHT WINDS SO I DECIDED TO DO A VISUAL APCH FOR RWY 35. UPON APCHING THE ARPT; I HAD REALIZED THAT I WAS NOT CONFIGURED FOR RWY 35 AND THAT R TFC FOR RWY 17 WOULD BE A BETTER CHOICE. SO I PROCEEDED TO DO SO. DURING THE DOWNWIND PORTION OF THE FLT; I HAD REALIZED THE WX HAD DETERIORATED SIGNIFICANTLY AND WE WERE ENCOUNTERING HVY PRECIPITATION. FROM MY CURRENT POS (DOWNWIND LEG) I WAS QUESTIONING VFR CONDITIONS. I FELT UNEASY ABOUT THE CIRCUMSTANCES AND ASKED CAPT TO TAKE OVER AND POSITIVE EXCHANGE OF FLT CTLS WERE EXECUTED AT THIS TIME. CAPT CONTINUED ON THE DOWNWIND PORTION OF THE FLT AND SECONDS LATER DECIDED IT WOULD BE A GOOD CHOICE TO SET UP FOR AN APCH. SO I CALLED UP ZKC AND REQUESTED RADAR VECTORS FOR THE ILS RWY 35 INTO GARDEN CITY; KS. EVERYTHING SEEMED NORMAL AT THIS POINT AND WE PERFORMED OUR NORMAL CHKLISTS. WE WERE CLRED FOR THE ILS RWY 35 APCH AND THEN WENT VISUAL ABOUT 4 MI OUT. THE APCH TO LNDG WAS STABILIZED AND THINGS DETERIORATED DURING THE FLARE TO ROLLOUT PORTION OF THE FLT. AIRSPD GOT LOW AND IN SECONDS WE LOST CTRLINE; DRIFTED OFF COURSE AND LOST DIRECTIONAL CTL. UPON LNDG WE VEERED OFF THE RWY; DIRECTIONAL CTL WAS REGAINED AND WE CAME TO A COMPLETE STOP HALFWAY OFF THE RWY. MEMORY ITEMS WERE COMPLETED AT THIS TIME AND WE BOTH SECURED THE ACFT. DEADHEADING CAPT ASSISTED ME IN THE EVAC PART OF THIS EMER. HE FIRST MADE SURE THE ACFT WAS FULLY SECURED AND THEN CALMLY AND CONFIDENTLY INSTRUCTED THE PAX TO EXIT THE AIRPLANE. I WAS STANDING AT THE BASE OF THE STAIRS AND WAS INSTRUCTING THE PAX ON WHERE TO GO. FIRE TRUCKS CAME TO THE SCENE IN MINS AND EVERYTHING WAS UNDER CTL. BOTH CAPT AND I WERE DRUG TESTED THAT NIGHT AND NO INJURIES WERE RPTED. SUPPLEMENTAL INFO FROM ACN 632368: NIGHT VISUAL LNDG INTO RWY 35 INTO GCK. DURING LNDG; LOST DIRECTIONAL CTL AND ACFT LEFT RWY. STOPPED ACFT AND PERFORMED PROP COLLISION DURING GND OPS CHKLIST. AFTER SECURING BOTH ENGS; WE EVACED PAX WITHOUT INCIDENT. SECURED ACFT.