A support structure for an aircraft seat includes load bearing spaced side members, each having elements for securing a seat for continuous movement between first and second positions, and a ground engaging portion. The structure further includes a stiffening web extending between the side members. The side members and the stiffening web substantially define a hollow box section of at least four sides to stiffen the side members, at least in the regions beneath the element securing the seat. The support structure allows other material than the conventional steel or aluminum constructions to be used for the support frame. For example, substantially all off the structural strength of the support may be provided by fiber reinforced composite materials.