ENVIRONMENTAL CONTROL SYSTEM

The present disclosure relates to a gas turbine engine (10) for an aircraft comprising: an engine core (11) comprising a turbine (17), a compressor (15), and a core shaft (26, 27); and an environmental control system mounted on the engine core comprising a first air passage (41) arranged to deliver air from outside the engine core to an aircraft cabin and/or for wing anti icing, a subsidiary compressor (42) located in the first air passage (41) and arranged to compress air in the first air passage, the subsidiary compressor being powered by the core shaft (26,27), and a second air passage (43) arranged to inject air from the compressor (15) into the first air passage.