Complex sentence: Performance was so close to that of the Hawfinch that a decision was deferrend until the aircraft had been evaluated by service pilots: the eventual choice of the Bulldog was made largely because it was easier to maintain.
Split into simpler sentences: Performance was so close to that of the Hawfinch that a deciion was deferrend until the aircraft had been evaluated by service pilots. The eventual choice of the Bulldog was made largely because it was easier to maintain.