THE ACFT HAD BEEN ON SALES DEMONSTRATION FLTS AND WAS ON A DELIVERY FLT FROM MEMPHIS, TN TO DALLAS, TX. THE PLANE WAS OBSERVED DEPARTING AT 1550 CDT IN A MAX PERFORMANCE CLIMB. RADAR INFO FROM MODE C OF THE TRANSPONDER RETURNS INDICATED THAT THE ACFT CLIMBED FROM 1000 TO 16,000 FT IN 7 MIN AND 14 SEC. LEVEL FLT WAS INDICATED AT 16,300 FT FROM 1558:16 TO 1601:17 CDT. THE LAST ALT RETURN WAS FROM 16,000 FT AT 2201:07. TWO MORE RETURNS WERE RECEIVED AT 2201:49 & 2202:08, BUT WITH NO ALTITUDE READ-OUT. AT ABOUT THAT TIME, THE ACFT WAS OBSERVED SPIRALING DOWN, COUNTERCLOCKWISE, WITH A PORTION OF THE LEFT WING MISSING. THE WING TIP (OUTER WING PANEL OUTBOARD FROM ABOUT WING STATION 190), LEFT AILERON AND LEFT ENGINE TAIL CONE PANEL WERE FOUND ABOUT 3 MI FROM THE MAIN WRECKAGE IMPACT POINT. AN EXAMINATION REVEALED THAT THE WING PANEL SEPARATION OCCURRED UPWARD FROM POSITIVE OVERLOAD FORCES. NO EVIDENCE WAS FOUND OF FATIGUE OR PRE-EXISTING FAILURE. LIGHT TO MODERATE TURBULENCE WAS REPORTED BETWEEN 14,000 AND 18,000 FT MSL.