A release system for a tether line includes a housing having a side that is at least partially open. A tether lead within the housing is adjacent to the side of the housing. A release mechanism in the housing includes a shackle having a closed end and an open end. The shackle is disposed in the housing at a portion therein that is lower than that of the tether lead. The release mechanism also includes a hinge for mounting the shackle within the housing. In a tether-retention mode, the open end of the shackle faces the top of the housing and the shackle is prevented from rotation about the hinge. In a tether-release mode, the shackle is free to rotate about the hinge under gravity wherein the open end of the shackle rotates to face the side of the housing.