ACFT WAS SCHEDULED FOR AN INSTRUCTIONAL FLT. DURING THE WX BRIEFING, THE CFI TOLD THE FSS SPECIALIST THAT THE FLT WOULD INCLUDE ENG-OUT PRACTICE. WITNESS STATEMENTS INDICATE THAT THE ACFT ROLLED SHARPLY TO THE RT AND NOSED DOWN AFTER ATTAINING ABOUT 100 FT OF ALT DURING THE CLIMB AFTER TAKEOFF. THE ACFT STRUCK THE GROUND LEFT PROP AND LEFT WING TIP FIRST, IN AN INVERTED FLT ATTITUDE. DURING THE POST ACCIDENT INVESTIGATION, THE RT ENG PWR LEVER WAS SUBJECTED TO LAB EXAM AND IT WAS FOUND THAT THE LOWER AFT PART OF THE LIFT GATE DETENT WAS WORN. THIS CREATED A RAMPING EFFECT BETWEEN THE ROUNDED EDGE OF THE LIFT GATE AND THE FLT IDLE STOP. A WORN LIFT GATE DETENT WOULD ALLOW THE POWER LEVER TO INADVERTENTLY BE MOVED INTO THE BETA RANGE, CAUSING ASYMMETRICAL DRAG AND DEGRADED AIRPLANE PERFORMANCE, PARTICULARLY IN CRITICAL PHASES OF FLIGHT.