In this paper study of Gas Tungsten Arc Welding (GTAW) process used for Aerospace application, the material used is Maraging steel (MDN250).The weld defects are a major concern leading to rework, higher costs and thus affecting the delivery schedule of the job. The process starts with Welding of long seams and circular seams in the job, and subsequently carrying out the NDT to find any defects during welding. A number of defects are being observed in the welding Process. Defects in welding may be found out in two methods, i.e. by Radiographic Tests and by Ultrasonic Tests. The paper deals with an application of Six Sigma DMAIC (Define–Measure- Analyze-Improve-Control) methodology in an industry which provides a framework to identify, quantify and eliminate sources of variation in an operational process in question, to optimize the operation variables. Six Sigma improves the process performance of the critical operational process, leading to better utilization of resources, decreases variations & maintains consistent quality of the process output.