FILE PHOTO: Grounded Boeing 737 MAX aircraft are seen parked in an aerial photo at Boeing Field in Seattle, Washington, U.S. July 1, 2019. Picture taken July 1, 2019. REUTERS/Lindsey Wasson/File Photo

(Reuters) - United Airlines Holdings UAL.O may not receive complete delivery of Boeing Co's BA.N 737 MAX even by next year, Chief Financial Officer Gerry Laderman said on a conference call with investors, underscoring the uncertainty surrounding the aircraft's return to service.

Chicago-based United was expecting 16 MAX aircraft this year, but deliveries have been frozen since mid-March when regulators worldwide grounded the jet after two deadly crashes in Indonesia and Ethiopia.

“None of Boeing’s customers know right now exactly when they’re going to get their scheduled MAX deliveries. But one could assume that we won’t fully catch up next year,” Laderman said.

United has scheduled flights without MAX till Nov. 3 and executives said they do not expect the aircraft, which still needs regulatory approval for new software and pilot training, to fly anytime before.