Abstract: There is disclosed a method of washing a gas turbine engine (10) of a type having an anti-icing arrangement comprising a fluid delivery system (33) configured to deliver a flow of hot gas to a region (36) of the engine during operation of the engine. The method comprises the steps of: connecting a supply of cleaning liquid to said fluid delivery system (33); creating a flow of said cleaning liquid through at least part of said fluid delivery system (33) for delivery to said region (36) of the engine; and directing said cleaning liquid towards internal components (25, 27, 30) of the engine.