AT ski binding adaptor for alpine ski touring and downhill, including a floating heel lock assembly and multifunctional rotatable locking arms. Ski bindings are mounted on an adaptor mounting plate, channel or beam assembly that pivots at the toe. The heel lock mechanism “floats” on a rail or rails to accommodate ski flex, and includes a multi-position climbing bar or heel riser. The floating heelblock and locking mechanism are interconvertible for different ski modes: in fixed heel-mode—the locking arms act to firmly secure the heel to the ski for aggressive downhill conditions or riding style, and in free heel mode—the locking arms may be configured to support touring and climbing configurations. The ski binding adaptor with floating heel lock mechanism is optionally compatible with a range of alpine ski touring and downhill bindings.