THE ACFT COLLIDED WITH THE GROUND AS THE PLT, WHO WAS NOT CURRENT FOR NIGHT/INSTRUMENT FLT, TRIED TO MANEUVER BENEATH A LOW OVERCAST ON A DARK NIGHT. ALTHOUGH SERIOUSLY INJURED DURING THE ACCIDENT SEQUENCE, THE PLT WAS ABLE TO TELL RESCUE WORKERS THAT HE 'WAS TURNING AROUND AND JUST FLEW INTO THE GROUND.' THE ACFT WRECKAGE WAS NOT LOCATED FOR APRX 3 HRS DUE TO POOR VIS. THE ACCIDENT TIME WAS POSSIBLY AS EARLY AS 1800 CST FROM ACFT PERFORMANCE PROJECTIONS AND THE EARLIEST CALLER REPORTING THE ACCIDENT CONTACTED COLLIN COUNTY SHERIFF'S DEPUTY AT 2121 CST AFTER A FARMER FOUND THE WRECKAGE. DURING THE ACFT GROUND BOUNCES/SLIDE AND BREAKUP, AN 80 LB DOG, HEAVILY SEDATED AND UNRESTRAINED, WAS THROWN FOWARD FROMA REAR SEAT AND POSSIBLY COLLIDED WITH THE RT FRONT SEAT PAX WHO WAS RESTRAINED BY A LAP BELT. FATAL INJURIES TO RIGHT FRONT SEAT PAX WERE CONSONANT WITH INSTRUMENT PANEL IMPACT AND A BLOW TO THE BACK AND HEAD. NO SHOULDER HARNESSES WERE AVAILABLE.