Abstract: A bypass turbofan gas turbine engine (10) is started by means of electric starter motor (26) mounted directly about a downstream end or upstream of the low pressure spool (12) of the engine. This causes air to be driven by a fan (16) through a bypass duct (32) around the engine casing (28). Closures (34) close to substantially seal an outlet of the bypass duct (32), and the air is directed into a combustion chamber (24) of the engine and through the turbines (22,23), causing the high pressure spool (14) to pick up speed for starting.

Abstract: A gas turbine engine (2) comprises a fan unit (4, 18, 36, 42, 44, 46) in flow relationship with an engine core and a bypass duct, of which said engine core and bypass duct (16) are in parallel flow relationship with each other. The engine core comprises a compressor (6), a combustor (8) and a turbine (10), with an inner casing (12) provided around said engine core which defines the engine core intake (32). The bypass duct (16) is defined by an outer casing (14) radially spaced apart from the fan unit (4, 18, 36, 42, 44, 46) and the inner casing (12) along at least part of the length of the gas turbine engine (2). Bypass air compression means (28) are provided such that, under substantially all engine power conditions, air at exit from the bypass duct (16) is at a greater pressure than air delivered to the engine core intake (32).