twa's st. louis hub shrank after the acquisition, due to its proximity to american's larger hub at chicago's o'hare international airport. as a result, american initially replaced twa's st. louis mainline hub with regional jet service (going from over 800 operations a day to just over 200) and downsized twa's maintenance base in kansas city. in september 2009, american airlines announced its intent to shut down the st. louis hub it inherited from twa and, in october 2009, american airlines announced its intent to close the kansas city maintenance base by september 2010.