Nuts and Studs at Fault

According to a just-released accident investigation board report, “material failure of some of the mounting nuts and studs which secure the intermediate gear box (IGB) to the tail pylon” caused the Sept. 7, 2007 crash of an MH-53 Pave Low helicopter at the Eglin Range Complex in Florida. There were no serious injuries, but the aircraft received about $8.6 million in damage from what Air Force Special Operations Command termed a “hard landing.” The crew from the 20th Special Operations Squadron at Hurlburt Field, Fla., was about 12 minutes into a night-vision goggle training sortie when the tail scanner detected a “worsening vibration.” During the 45-second return to the landing zone, the crew observed “abnormal oscillations in the engine and rotor instruments,” followed by a loss of rotor speed. (Executive Summary, caution: large file)