Interesting example - but some time what we miss out is the fact - Model is not broken, its because we could not model it correctly due to lack of standards - some facts to know!!!

1. Numbering used in the flights were first developed for the purpose of identifying flights in each airports - and the numbering system varies from airlines to airlines/country to country... (You can imagine the challange when 2 airlines merge that are from 2 country !!)

2. The way numbering is done though has a standard - but do not have a industry standard, an Example - one airline will use east/north bound flight numbers to be in even numbers & West/south bound to be odd numbers - and other would use odd numbers for outbound and even for inbound - so there is no standards set across the industry on the numbers!

3. Now, IATA - a Regulatory body had attempted to solve this challange in flight numbers and had come up with standard manual - but still not widely followed across the world!!

With all of the above challange - its not possible to build a standard data model that can be used across any airlines when it comes to Flight number field and usage/relationship etc - to complicate the above fact airline merger/ Flight accidents ( you do not reuse the number when u have a flight accident ) fuels the data challange.

This is a classical example of how Compliance, Change in business environment, lack of standards - can lead to business impacts