Complex sentence: The first flight, scheduled after the design was finalized, was to take place in the second quarter of 2012, but was delayed to 2013, and then further delayed to spring 2014 due to delays in the procurement of engines.
Split into simpler sentences: The first flight, scheduled after the design was finalized, was to take place in the second quarter of 2012. It was further delayed to spring 2014 due to delays in the procurement of engines.