Apparatus for maintaining the temperature of a component of a gas turbine engine below a predetermined maximum working temperature comprises a reservoir for a cooling fluid having a boiling point below the working temperature and in which the component is immersed or with which it is in contact. Assigning an instance of a CPD to a design element can indicate, for example, whether the element can be switched on and off, or whether the element can operate over a range of voltages. The base station sets an indicator in a control channel allocation of a frame. Within the selected amount of copies, an error of a defined error type or of a defined feature, which is detected on at least one of the copies, is evaluated in relation to at least one error of another type or feature detected on the same copy, or another copy of the selected amount.