The paper presents the problems arising in the process of repairs of aircraft (AC) components made of aluminium alloys during arc welding with the TIG (tungsten inert gas) method. The paper provides information on the rules applicable in the welding process qualification. The procedure algorithm when qualifying the welding process was presented in accordance with PN-EN ISO 15614-2. The main causes and factors affecting the formation of defects and welding imperfections were described and classified. The principles of preparing the components for welding and selection of a binder were discussed. The issue of effect of the welding parameters on the formation of defects and welding imperfections in relation to PN-L-01426 standard was raised. The application of computed tomography in assessment of the welded joints was described and tomograms from tests of butt welds of aluminium alloys made of the AW 5754 grade aluminium alloy were presented. On the example of the tomograms, the welding imperfections and defects formed in the tested joints were discussed. The usefulness of computed tomography in assessment of the welds’ quality was shown.