Figures are indicative only. For all you know, Indigo will cancel half their orders mid way, and decide to go with a widebody to ramp up international operations??
Who knows whats to happen tomorrow! We might even face another global recession before we know it!!
Just want to give an indicative that it's all good.
Besides, I doubt they will phase out aircraft even in the next 15 years. AI's A320 fleet has an average age of about 17 years!!!!! Ofcourse, thats AIR INDIA! But I doubt Indigo will start phasing out before 2020, if at all.