Two big reasons: First, Willie Walsh was named CEO, and his strong track record in aviation has made investors feel optimistic about IndiGo's direction.
Second, worries about a massive hike in aviation fuel prices were cleared up. It turns out only chartered flights will see those steep increases.
For regular airlines like IndiGo and SpiceJet, fuel costs did go up by 8.5%, but that was much less than feared and helped calm nerves in the market.