CHICAGO — United Airlines CEO Oscar Munoz, in an effort to assure passengers, vowed to be aboard the airline’s first flight on a Boeing 737 Max once regulators agree to let the aircraft begin flying again.

Regulators around the world grounded the 737 Max in March after the plane was involved in deadly crashes in Ethiopia and Indonesia. Boeing has said it completed updates to software linked to the crashes, but regulators still need to review its fix and plan for additional pilot training.

Even after regulatory agencies clear the 737 Max to begin flying again, Munoz said United knows it will take more to get passengers comfortable getting on board.

“Just because somebody says it’s safe, you as the flying public aren’t just going to get on the aircraft,” Munoz said Wednesday.

It remains unclear when regulators will allow carriers to resume flights on the Max.

United, American and Southwest have 14, 24 and 34 of the 737 Max aircraft in their fleets, respectively — aircraft they’re now forced to keep idle heading into the busy summer travel season.

Last month, United canceled flights on the 737 Max through early July, saying efforts to cover flights that would typically use one of the grounded aircraft would get more challenging as summer travel picked up.

American Airlines and Southwest Airlines have extended cancellations into August.