The best September quarter in IndiGo 's operating history should give sufficient confidence to investors in the stock of the airline that now has a 38 per cent share of the local aviation market IndiGo's tenacious grip on one of the world's fastest-expanding airline travel markets is reflected in its ability to raise yields in the quarter that coincides with monsoon rains across most parts of India The average revenue per kilometer per customer rose 9 per cent to Rs 3.57 in the three months to September, and analysts estimate that the yield and load factor would improve to Rs 3.63 and 86 per cent, respectively, by FY18 end.Tailwinds from the first half of the year should aid IndiGo in the second -and likely get more investors on board. The management has said that it would add 14 per cent additional capacity in the December quarter and for FY18, it would add 19 per cent more seats.Since the second half is seasonably better, the decision to add capacity further enhances the optimism about the company's earnings . Also, given this enhancement in capacity, analysts would be keenly monitoring how successfully the company raises its per-kilometerper-passenger yield, which is set to climb to Rs 3.63 by FY end.In the September quarter, due to improved capacity and rise in ticket prices, the company's revenues from operations climbed 27 per cent to Rs 5,291 crore, resulting in a fourfold increase in net profit at Rs 551 crore.Furthermore, the company's new fleet of ATR72-600 aircraft, which will be used for flying on regional routes in India, also comes at an opportune time. The regional service should contribute in enhancing the company's earnings per share (EPS) for FY18 by 8-10 per cent.Over the next year, the promoters are expected to bring down their stake to 75 per cent from the present 77.9 per cent, thus creating more liquidity and investor interest in the scrip.On the valuation front, InterGlobe Aviation (the operator of IndiGo) is trading at a price to earnings (PE) multiple of 21.8 for FY18 estimated earnings, translating into a 50 per cent premium over global benchmarks.Still, the premium seems justified as IndiGo is the clear leader in one of the fastest growing aviation markets in the world, and its earnings are expected to rise 55 per cent this FY.