UPON TOUCHDOWN ON THE GRASS RUNWAY, THE PILOT APPLIED THE BRAKES, AND THE AIRPLANE SKIDDED OFF THE END OF THE RUNWAY, DOWN A STEEP BANK INTO A WOODED AREA. THE AIRPLANE STRUCK TREES AND THE WINGS SEPARATED. ACCORDING TO THE PILOT'S STATEMENT, 'RUNWAY WAS FROST COVERED GRASS. BRAKES OPERATED CORRECTLY, NO MECHANICAL MALFUNCTION.'