Both wings buckled rear to the front and failures occurred in stringers, spars and ribs. Ribands bolt the planking to the stringers. Some systems combine stringers and supports into steel or aluminum trusses. An idealized wing structure is made up of spars, stringers, and skin segments. Some aircraft use a combination of both stringers and longerons. It has steel stringers, timber treads and a steel balustrade. The fuselage was formed of stringers to which the fuselage skin was riveted. The pontoons were linked together using wooden stringers called "balks". The initial tracks were built with granite stringers topped by strap iron rails. The intertank aluminium structure utilizes skin stringers with stabilizing frames. These frames are then joined with lightweight longitudinal elements called stringers. Attached wood stringers carried a fabric skin. The top deckboards are then affixed to the stringers to create the pallet structure. Longerons are used in conjunction with stringers to form structural frameworks. NASA also performed backscatter scanning of the lower liquid hydrogen/intertank flange stringers on 29 November.