System for washing a gas turbine engine (1). The system comprises a spray device (33; 90) including at least one nozzles (54) adapted to inject liquid into an inlet (110) of said engine during a washing operation; a wash unit (31, 35) adapted to distribute said liquid to said spray device (33; 90); and a positioning device (34) adapted to move said spray device in three dimensions, thereby enabling a positioning of said spray device in a washing operation position in said three dimensions relative said engine inlet (110) without any contact between the spray device (33; 90) and the engine (1). The invention further relates to a vehicle for making the inventive system mobile and to a mobile system for serving a gas turbine engine (1) comprising a mobile vehicle carrying the washing system and a liquid collecting unit (116) comprising a collecting device (114) adapted to collect waste wash liquid emanating from the engine during a washing operation of the engine.