Based on request of a low cost airline, modification with cabin reconfiguration of 16 aircraft was performed in maintenance organisation. The main contribution was optimisation of modification process. Initially, 21 working days were predicted for each aircraft or 336 days for whole series. With process optimisation in two steps we managed to reduce groundtime to 12 days per aircraft or 209 days for the whole series. In first optimisation step, prefabrication of components was implemented and with this groundime was reduced by 7 days per aircraft. Second optimisation step includes design and manufacturing of templates, which reduced total groundtime of each aircraft by additional 2 days. With use of optimised process aircraft can be returned to revenue service sooner, which presents positive economical contribution to the airline and the maintenance center.