Powerplant with multiple integrated gas turbine engines

A powerplant, comprising:

• a first gas turbine engine including a first fan section, a first compressor section, a first combustor section, a first turbine section and a first core flowpath extending sequentially through the first compressor section, the first combustor section and the first turbine section;
• a second gas turbine engine including a second fan section, a second compressor section, a second combustor section, a second turbine section and a second core flowpath extending sequentially through the second compressor section, the second combustor section and the second turbine section;
• a first engine bypass flowpath outboard of the first core flowpath and extending sequentially through the first fan section and the second fan section;
• the first gas turbine engine arranged forward of the second gas turbine engine along a common axial centerline;
• a second engine bypass flowpath outboard of the second core flowpath, the second core flowpath and the second engine bypass flowpath independently fluidly coupled with and downstream of the first engine bypass flowpath;
• and
• a flow control system configured to fluidly couple a first inlet and a first exhaust to the second core flowpath during a first mode, the flow control system configured to fluidly couple the first inlet and the first exhaust to the second engine bypass flowpath during a second mode, and the first core flowpath extending sequentially through the first compressor section, the first combustor section and the first turbine section between the first inlet and the first exhaust.