Private equity investors, known for their jet-setting ways of landing deals, have become hooked on the air transport business. Some fear an airplane investment bubble is forming.

Attracted by a global rise in passenger numbers, an explosion of budget airlines and healthy profits, private equity funds have poured $207bn into financing commercial airliner deliveries since 2009, according to Boeing data, during which time almost $900bn was spent on new jetliners. But with returns dampening, some investors worry the historically cyclical sector is overinflating.