Last time I checked, Doncaster airport's passenger flights fall almost entirely into 2 categories
-taking local residents on holiday to a beach
-making it easier for migrant labour living locally to visit family in central/eastern Europe.
There appears to be almost nobody at Doncaster airport flying for business and wearing a suit. DSA seem unable to support traffic to major non holiday cities in western Europe; not even a daily service to Paris or Amsterdam.
There is already a direct bus from the centre of Doncaster adjacent to the train station, direct to the airport. Doncaster has an excellent train service to/from the region. Is there really a commercial need for a significant infrastructure project, when increasing the existing local bus frequency might suffice instead ? Aberdeen, Belfast, Bristol, Cardiff, East Midlands, Leeds and Glasgow seem to manage much higher passenger numbers while relying on buses for public transport.