Yes, where the rest of the panel is sound and the replacement rail matches the existing construction. If several rails or many boards are damaged, replacing the complete panel may be the more reliable repair.
Yes. A damaged fence panel backrail can be replaced where the surrounding boards and the rest of the panel remain sound enough to refix. The replacement rail must match the dimensions and layout of the existing panel rather than being chosen simply because it is described as a fence rail.
East Coast Fencing supplies a 1.83m x 75 x 32mm fence panel backrail for compatible panel construction and repairs. The rail sits behind the visible vertical boards and provides a horizontal fixing line through the panel.
Before repairing, check more than the single failed component. A 75 x 32mm backrail is not automatically interchangeable with every fence-panel rail. Measure the existing section and inspect the boards around it. If several rails have failed or a large proportion of the boarding is decayed or damaged, rebuilding around one new rail may not be worthwhile.
During a suitable repair, support the panel while the damaged rail is removed so the boards do not shift out of alignment. Set the replacement rail level and use exterior-grade fixings appropriate for the timber being joined. A 1.83m rail can be trimmed if the existing panel requires it, but the actual panel width should be measured first.
Loose backrails and related components can be found under square rails. If the damage is extensive, compare the cost and work involved with fitting a complete replacement panel instead.