Koush, flights apply only to cities having an airport and having direct flights to Chennai. In the entire route of the train, only 3 cities fit the bill - ADI, Mumbai and Pune. Passengers from other places dont have a flight option.
So its either travel first to either of these three congested cities and then fly, or directly board an AC train from your own city.
Also, show me flight tickets at 20% higher than 3AC fare, say one month before date of journey - I think only Pune has such cheap...
more... flight fares to Chennai, not ADI, not Mumbai either.