WITNESSES HEARD THE SOUND OF AN ACFT WITH THE ENG AT HIGH RPM. SHORTLY AFTER THAT, THEY SAW THE ACFT IN A LEFT SPIN WITH THE ENG REMAINING AT FULL POWER. THE ACFT CONTINUED SPINNING UNTIL IT CRASHED & BURNED. THE WITNESSES NOTICED THAT WHEN THE PLANE WAS DESCENDING ABOUT 3 FT OF THE OUTBOARD PORTION OF THE LEFT WING HAD FAILED, BUT WAS STILL ATTACHED TO THE ACFT. AN EXAM OF THE WRECKAGE VERIFIED THAT THE LEFT WING TIP HAD FAILED PRIOR TO IMPACT. FIRE DAMAGE WAS SO EXTENSIVE THAT THE MODE OF FAILURE COULD NOT BE DETERMINED; HOWEVER, THERE WAS EVIDENCE THAT THE LEFT WING TIP HAD FAILED UPWARD & AFT. FURTHER INVESTIGATION REVEALED THAT THE ACFT HAD BEEN BLOWN INVERTED ON 11/23/83 BY STRONG WINDS. AT THAT TIME, THE LEFT WING TIP WAS BROKEN & A WING RIB WAS CRUSHED; ALSO, THE RUDDER, VERT STABILIZER, PROP & RIGHT WING STRUT WERE DAMAGED. NO ENTRIES HAD BEEN MADE IN THE ACFT LOGBOOKS SINCE THE ANNUAL INSPECTION ON 8/15/83. THE EXTENT OF THE REPAIRS FROM THE WIND DAMAGE COULD NOT BE DETERMINED.