Component of the intraflagellar transport (IFT) complex B required for transport of proteins in the motile cilium. Required for transport of specific ciliary cargo proteins related to motility, while it is neither required for IFT complex B assembly or motion nor for cilium assembly. Plays a key role in maintaining the integrity of the IFT complex B and the proper ciliary localization of the IFT complex B components. Essential for maintaining proper microtubule organization within the ciliary axoneme. Component of the IFT complex B. Belongs to the IFT56 family.