Aircastle Ltd. and its Japanese partner are planning to purchase as many as 10 new narrow-body jets in deals with airlines as the lessor bets on growing demand for travel in Asia. The jets may cost as much as $400 million, Chief Executive Officer Ron Wainshal said in an interview in Tokyo Tuesday. Stamford, Connecticut-based Aircastle formed a partnership with IBJ Leasing Co., an affiliate of Mizuho Financial Group Inc., in February. Aircastle owns 25 percent of the venture. The lessor is building deals in Japan after Marubeni Corp. first bought a stake in the company three years ago, becoming its largest shareholder. Spurred by strong economic growth in the past decade, Asia is on course to beat the U.S. as the biggest plane-leasing market in two decades. That potential has lured billionaires such as Li Ka-shing and budget-carrier pioneer Tony Fernandes to the industry. “Our partners are relying on us to have skin in the game,” said Wainshal. “They want us to find good deals.” Aircastle, which has 153 planes in its fleet, will buy the planes from airlines, who receive discounts from the manufacturer’s list prices. The airline then leases the jet back for operations.