THE ACFT WAS ON A FLT FROM LINCOLN, KANSAS TO ENGLAND, ARKANSAS. WITNESSES OBSERVED THE ACFT FLYING ERRATICALLY, NEAR A LAKE, CLOSE TO THE DESTN. THEY ATTRIBUTED THIS AS TRYING TO GAIN THEIR RECOGNITION IN THE FORM OF A GREETING. THE ACFT SUBSEQUENTLY CRASHED WHILE FLYING TOWARD THE LAKE. AN INVESTIGATION REVEALED EVIDENCE THAT IT HAD ENTERED A DIVE & IMPACTED THE GND AT A HIGH RATE OF SPEED BEFORE ARRESTING THE DESCENT. NO PREIMPACT PART FAILURE OR MALFUNCTION OF THE ACFT OR ENG WAS FND. THE TOXICOLOGY TESTING REVEALED THE PRESENCE OF WIDELY VARYING LEVELS OF ETHANOL IN THE PILOT'S BLOOD (79 MG/DL OR 0.079%), LUNG (65 MG/DL), & SPLEEN (36MG/DL), AS WELL AS A CONSIDERABLE AMOUNT (127 MG/DL)IN HIS URINE. THE TOXICOLOGIST INDICATED THAT SOME OF THE ETHANOL MAY HAVE BEEN FROM PUTREFACTION, BUT SOME WAS FROM PRE-ACCIDENT INGESTION BY THE PILOT.