What was found
(CAN) APU SHUT DOWN BY ITSELF UPON LANDING AT APROX. 100 KTS. INVESTIGATION REVEALED THAT 2 BOLTS MS9556-45 SECURING APU INLET DOOR ARM TO CLAMP WERE NOT TORQUED PROPERLY AND INLET DOOR SHAFT SLIPPED AND CLOSED DOOR UPON FINAL LANDING DUE TO VIBRATION. APU SHUT DOWN WAS IMMINENT. ATTEMPT TO RESTART DURING TAXI WAS UNSUCCESSFUL. IN 2 PREVIOUS FLIGHT, APU SHUT DOWN OCCURRED AT 41000 FT AT 4.5 HRS. DOOR RIGGING WAS ADJUSTED BUT REAL CAUSE NOT YET DISCOVERED AT THAT POINT. 2 BOLTS WERE RETORQUED AND FUNCTIONAL CHECK CARRIED OUT AND FOUND SERVICEABLE.