During the landing roll the aircraft began to swing to the right. The pilot attempted unsuccessfully to correct the swing by applying left brake and rudder. Because of the likelihood of striking a parked aircraft he then induced a ground loop to the right and the aircraft was brought to a stop. An inspection of the aircraft revealed that the right maingear had unlocked and the aircraft had settled on the right float. No fault could be found with the landing gear system. The gear collapse was consistent with there being insufficent hydraulic pressure available to hold the gear locks in position during the landing. The post accident inspection revealed that the hydraulic pump switch, which is located next to the electric fuel boost pump switch, was in the off position. It is likely that the hydraulic pump switch was inadvertently selected off after the previous take-off.
