This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
Yes, There can be 1 to many relationship between flight - equipment. But you have to take in to account TIME. At a certain time (i.e. when the flight in on air) there is always 1-to-1 relationship. Also At the planning time (travel planning) the airline has to mention that this flight will have A320 or A330. Only in some situation this changes say the plane not available or something.