BOMBARDIER AEROSPACE made history this month with the first flight of its new large commercial jet. The launch marked the breaching of the Boeing-Airbus duopoly that has ruled the skies since 1997, when McDonnell Douglas was taken over by Boeing. The CS 100, carrying 110 passengers, will compete with Boeing 737s and Airbus A320s, especially once a bigger version with 135 seats plane takes off next spring.