A wing structure is provided, wherein the wing structure comprises; an upper covering, a lower covering, and a spar, the spar comprising; a spar web, an upper spar cap attached to the upper covering, and a lower spar cap attached to the lower covering, the wing structure also comprising a face spaced apart from the spar web extending between the upper and lower spar caps. The wing structure is arranged to contain fuel in a fuel containment area between the upper and lower coverings on one side of the spar web. The upper and lower spar caps extend from the spar web only on the other side of the spar web to the fuel containment area.