THE ACFT WAS OBSERVED TO FLY NEAR POWER LINES, THEN ROLL INVERTED, CRASH & BURN IN A WOODED AREA. THE 4 OCCUPANTS RCVD MULTIPLE IMPACT INJURIES WHICH WERE FATAL. THE ACFT WAS DESTROYED BY THE IMPACT & POST CRASH FIRE. SVRL WITNESSES RPRTD THE ENG POWER WAS INTERMITTENT, BUT NO REASON WAS FND FOR THE RPRTD POWER LOSS. ALTHOUGH SOME WITNESSES ON THE GROUND THOUGHT THE ACFT STRUCK THE POWER LINES, AN AIRBORNE WITNESS (WHO SAW THE ACDNT) SAID IT DID HIT THE LINES. NO PHYSICAL EVIDENCE OF A POWER LINE STRIKE WAS FOUND. TOXICOLOGY CHECKS OF THE PLT SHOWED MEASURABLE LVLS OF ALCOHOL & BUTALBITAL. CHECKS OF HIS LIVER TISSUE AT 2 LABS SHOWED APRX 0.07% ALCOHOL, ALTHOUGH A 3RD LAB ONLY DETECTED ALCOHOL (0.05%) IN KIDNEY TISSUE. THE PLT'S WIFE SAID HE HAD USED FIORINAL, A PRESCRIPTION DRUG FOR HEADACHES. BUTALBITAL IS AN ACTIVE INGREDIENT OF FIORINAL & IS A BARBITURATE WITH SIDE EFFECTS OF DROWSINESS & LOSS OF ALERTNESS. ALSO, THE EFFECTS OF BUTALBITAL ARE ADDITIVE WITH THOSE OF ALCOHOL. ON 10/28/85 (DATE OF MED CERT), THE PLT RPRTD HE HAD 400 HRS OF FLT TIME.