A method for operating an engine is disclosed. The method may include supplying air from a primary air supply unit to an intake conduit. The method may also include supplying air to the engine from the intake conduit. The method may further include selectively supplying air from a secondary air supply unit to the intake conduit. In addition, the method may include maintaining an air fuel ratio between a first threshold value and a second threshold value during an increase in engine load increase by controlling a supply of air from the secondary supply unit to the intake conduit.