UPDATE 1-Indian airline IndiGo heads for up to $400 mln IPO amid travel boom - sources

MUMBAI/NEW DELHI, March 27 (Reuters) - India's biggest airline by market share, IndiGo, is preparing to file a draft prospectus by May for a stock listing to raise $300 million to $400 million, two people with knowledge of the plans said, aiming to cash in on a boom in budget air travel.