The crossrail beneath the handrail on this deck had decayed and at one corner the end was no longer attached to the post. The last 400mm of crossrail was removed and replaced with a new piece, joined to the intact section.
Mark a 45º line just before a picket across the old crossrail with a pencil, then cut along the line using a handsaw to remove the damaged section of crossrail. Sand the cut edges to remove any splinters.
Measure the new section length and cut a new piece to size, square-cutting one end to butt into the post and matching the mitre on the other end. Apply construction adhesive to the ends and secure with screws.
Reposition the pickets and check they are plumb. Drill pilot holes and attach the pickets to the crossrail with 65mm x 8g stainless steel screws. Drive the screw heads below the surface and fill holes with putty, then apply paint.