What was found
(CAN) WHILE ON GROUND AN ACFT WAS IN A CLEANING STA GETTING PREPARED FOR THE NEXT FLIGHTS (APU RUNNING), WHEN THE CLEANING AGENTS HEARD A HUGE BANG, SIMULTANEOUSLY THE APU DOORS SEPARATED AND FELL TO THE GROUND. APU FIREWALL, TAIL SECTION AND DOOR DAMAGE FOUND. 2 SIMILAR CASES REPORTED BY THE AOM 8-400-375 & SB-84-49-0. OPERATOR`S APU FADECS HAD BEEN ALREADY UPGRADED TO VERSION 3.0. APU FADEC SERIAL NR 0220, SOFTWARE VERSION: 03.00.000 INVESTIGATION INTO APU CONCLUSIVE EVENT.