About 130 of the U.S. Air Force’s single-seat A-10 Warthogs have been grounded over concerns about wing fatigue cracks. The 30-year-old planes were all made with “thin-skin” wings designed to reduce weight, but mechanics working on the planes noticed some wings had started developing fatigue cracks, Reuters reported. There have been no accidents as a result of the cracks. The grounded plans represent about a third of the Air Force’s fleet of Warthogs. Those made with thicker wing skins aren’t affected, and Air Force said, and the groundings won’t affect their ability to deploy aircraft. Some of the grounded planes had been used in Iraq and Afghanistan to provide air support for ground operations. Last year, the Air Force awarded a $2 billion contract to Boeing to replace the wings on the planes, which were originally made by Fairchild Industries.