THE ACFT WAS ON A NGT INSTRUCTIONAL FLT WITH 2 MULTI-ENG INSTRUCTOR PLTS AT THE CONTROLS & A RATED PLT OCCUPYING A REAR PAX SEAT. THE RGT FNT SEAT OCCUPANT WAS AN EXPERIENCED MULTI-ENG PLT WITH 110 HRS IN THIS MAKE & MODEL; HOWEVER, HIS 2NDCLASS MED CERT WAS ISSUED IN JAN 1983. THE L FNT SEAT OCCUPANT HAD JUST RECEIVED HIS MULTI-ENG INTRUCTOR RATING & HAD ONLY 3 HRS IN THIS MAKE & MODEL. HE HAD A CURRENT MED CERT & WAS PRESUMED TO BE THE PLT-IN-COMMAND. THE AIRCREW MADE 2 PASSES OVER RWY 18, THEN MANUEVERED ONTO A DOWNWIND LEG OF THE PATTERN. ACCORDING TO WITNESSES, THE ACFT WAS NORTHEAST OF THE ARPT AT APRX 300 TO 400 FT AGL & MANEUVERING BACK TOWARD THE RWY WHEN IT ENTERED A STEEP DSCNT, CRASHED & BURNED.THE ACFT CRASHED NORTHEAST OF THE ARPT IN A WOODED AREA. IMPACT OCCURRED ON A SOUTHERLY HDG IN ABOUT AN 18 DEG DIVE. NO PREIMPACT PART FAILURE/MALFUNCTION WAS FND; HOWEVER, THE ACFT WAS EXTENSIVELY DAMAGED DURING IMPACT. TOX CHECKS OF THE PAX & RGT FNT SEAT OCCUPANTS SHOWED EACH HAD AN ALCOHOL LVL OF 0.117%. NO ALCOHOL FND IN THE L FNT SEAT OCCUPANT'S BLOOD