Billionaire investor George Soros’ investment fund has placed new bets on low-cost and ultra-low-cost U.S. airlines, going for fresh stakes in JetBlue Airways Corp., Spirit Airlines Inc. and Sun Country Airlines Holdings Inc., according to a filing late Wednesday.

Soros’ fund, which had invested in JetBlue JBLU in the distant past, has bought more than 370 million shares of the low-cost airline, which recently appealed a court ruling blocking its merger with Spirit.

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