UPDATE 1-Delta throws Bombardier a lifeline with deal to buy 75 CSeries

(Adds details, background) April 28 (Reuters) - Delta Air Lines Inc on Thursday ordered 75 CSeries CS100 planes worth $5.6 billion from Bombardier Inc, throwing a lifeline to a new aircraft program that is years late and billions of dollars over budget. The widely anticipated order marks a turning point for Canada's Bombardier as it strives to break into the fleets of top airlines globally and serve a niche market for 100-seat planes that larger rivals Boeing Co and Airbus Group SE h