A catheter assembly comprising: a leading end; a trailing end; a catheter having a main lumen; an expandable device having a proximal end and a distal end, the expandable device having a collapsed configuration and an expanded configuration having a diameter larger than the diameter of the collapsed configuration, and an intermediate configuration larger than the collapsed configuration and smaller than the expanded configuration, the expandable device positioned at the leading end of the catheter assembly, and the expandable device is a bifurcated stent graft having a trunk defining a trunk lumen and two legs (1007, 1009) extending from an end of the trunk and each defining a branch lumen in fluid communication with the trunk lumen; a constraining mechanism extending around the expandable device to releasably constrain the expandable device toward the collapsed configuration, said constraining mechanism comprising an axially displaceable sheath having a lumen extending between the leading end and the trailing end and a flexible film sleeve wrapped circumferentially around the expandable device, the expandable device positioned in the lumen of the axially displaceable sheath towards the leading end such that axial displacement of the sheath away from the expandable device exposes the expandable device; a pusher disposed in the lumen and axially slidable relative to the sheath to prevent movement of the expandable device with the sheath in response to the axial displacement of the sheath; a steering wire that extends through the main lumen of the catheter and is operatively coupled to the flexible film sleeve to allow axial bending of the expandable device in the intermediate configuration in response to selective displacement of the steering wire relative to the catheter; and a steering wire conduit configured to minimize contact and friction between the steering wire and surrounding components of the catheter assembly. a leading end; a trailing end; a catheter having a main lumen; an expandable device having a proximal end and a distal end, the expandable device having a collapsed configuration and an expanded configuration having a diameter larger than the diameter of the collapsed configuration, and an intermediate configuration larger than the collapsed configuration and smaller than the expanded configuration, the expandable device positioned at the leading end of the catheter assembly, and the expandable device is a bifurcated stent graft having a trunk defining a trunk lumen and two legs (1007, 1009) extending from an end of the trunk and each defining a branch lumen in fluid communication with the trunk lumen; a constraining mechanism extending around the expandable device to releasably constrain the expandable device toward the collapsed configuration, said constraining mechanism comprising an axially displaceable sheath having a lumen extending between the leading end and the trailing end and a flexible film sleeve wrapped circumferentially around the expandable device, the expandable device positioned in the lumen of the axially displaceable sheath towards the leading end such that axial displacement of the sheath away from the expandable device exposes the expandable device; a pusher disposed in the lumen and axially slidable relative to the sheath to prevent movement of the expandable device with the sheath in response to the axial displacement of the sheath; a steering wire that extends through the main lumen of the catheter and is operatively coupled to the flexible film sleeve to allow axial bending of the expandable device in the intermediate configuration in response to selective displacement of the steering wire relative to the catheter; and a steering wire conduit configured to minimize contact and friction between the steering wire and surrounding components of the catheter assembly.