A Boeing 737 MAX plane is seen during a media tour of the Boeing plant in Renton, Washington, U.S. December 7, 2015. [Reuters]
Boeing Chief Executive Dennis Muilenburg said he was confident the MAX would be back in service as early as October, but acknowledged for the first time that Boeing may have to slow or completely halt production of the 737 MAX, a step it has not had to resort to on any commercial plane for more than 20 years.