This Audit Query (AQ15-002) was opened on June 22, 2015 to investigate the timing and scope of Terex South Dakota, Inc. (Terex)?s determination and notification to NHTSA of a safety defect, as well as Terex?s compliance with reporting requirements under the National Traffic and Motor Vehicle Safety Act and regulations.On May 29, 2015, Terex submitted a Defect Information Report to NHTSA describing a safety defect in the Lower Boom of 2002 XT55 and XT60 series aerial devices installed on certain trucks, encompassing approximately 48 vehicles (NHTSA Recall No. 15V-353). Based on available information, NHTSA decided to investigate the scope of Recall No. 15V-353, along with the timeliness of Terex?s defect determination and notification to NHTSA. NHTSA also decided to investigate Terex?s compliance with reporting requirements for manufacturer communications under 49 C.F.R. ? 579.5, as the last document submitted by Terex pursuant to that requirement prior to the opening of this investigation was during the third quarter of 2009.Information obtained from Terex?s response to NHTSA?s Special Order in this investigation revealed that, following the first reports of cracks (as early as 2004) and stress testing conducted on the boom arms at the upper and lower cylinder connections (also in 2004), Terex created ?Z-Kits? 887 and 1290 to offer a preventative welding reinforcement on the affected units. Terex did not conclude these cracks or test results indicated a safety defect existed on the aerial devices and did not issue a safety recall at that time. Additional reports of devices developing cracks, an incident involving the failure of a boom arm that allowed an aerial device lift bucket to drop while occupied, and a report identifying a deficiency in the metal used by Terex to manufacture the boom arms prompted Terex to further investigate the cracks occurring in the XT series aerial devices. Terex?s testing and evaluations indicated that at the time of manufacture, the ma