Complex sentence: Prior to its bankruptcy in 2004 ATA Airlines planned turboprop service to several Indiana cities by its subsidiary, Chicago Express/ATA Connection, but the service was never started as Chicago Express Airlines was grounded in March 2005.
Split into simpler sentences: Prior to its bankruptcy in 2004, ATA Airlines had planned turboprop service to several Indiana cities. This service was to be operated by its subsidiary, Chicago Express/ATA Connection, but the proposed service was never started as Chicago Express Airlines was grounded in March 2005.