Boeing's 737 MAX

Boeing employees march up and down stairs entering and exiting Boeing 737 MAX during a media tour of the Boeing 737 MAX at the Boeing plant in Renton, Washington December 7, 2015. REUTERS/Matt Mills McKnight

Boeing employee Mike Laeuger is seen working on Boeing 737 MAX during a media tour of the Boeing 737 MAX at the Boeing plant in Renton, Washington December 7, 2015. REUTERS/Matt Mills McKnight

A Boeing 737 MAX is pictured during a media tour of the Boeing 737 MAX at the Boeing plant in Renton, Washington December 7, 2015. REUTERS/Matt Mills McKnight

A wing of the Boeing 737 MAX is pictured during a media tour of the Boeing 737 MAX at the Boeing plant in Renton, Washington December 7, 2015. REUTERS/Matt Mills McKnight

Boeing employee Mike Laeuger is seen working on Boeing 737 MAX during a media tour of the Boeing 737 MAX at the Boeing plant in Renton, Washington December 7, 2015. REUTERS/Matt Mills McKnight

A Boeing 737 MAX plane is seen during a media tour of the Boeing 737 MAX at the Boeing plant in Renton, Washington December 7, 2015. REUTERS/Matt Mills McKnight

The interior of an unfinished Boeing 737 MAX is pictured during a media tour of the Boeing 737 MAX at the Boeing plant in Renton, Washington December 7, 2015. REUTERS/Matt Mills McKnight

An employee is seen passing the nose of a Boeing 737 MAX during a media tour of the Boeing 737 MAX at the Boeing plant in Renton, Washington December 7, 2015. REUTERS/Matt Mills McKnight

The cockpit is pictured during a media tour of the Boeing 737 MAX at the Boeing plant in Renton, Washington December 7, 2015. REUTERS/Matt Mills McKnight

Boeing employees work on the tail of a Boeing 737 NG at the Boeing plant in Renton, Washington December 7, 2015. REUTERS/Matt Mills McKnight

Boeing employees work during a media tour of the Boeing 737 MAX at the Boeing plant in Renton, Washington December 7, 2015. REUTERS/Matt Mills McKnight

An engine of a Boeing 737 MAX is seen while the plane sits outside the hangar during a media tour of the Boeing 737 MAX at the Boeing plant in Renton, Washington December 8, 2015. REUTERS/Matt Mills McKnight

A portion of a painted Boeing 737 MAX fuselage is seen while it sits outside the hangar during a media tour of the Boeing 737 MAX at the Boeing plant in Renton, Washington December 8, 2015. REUTERS/Matt Mills McKnight

A Boeing 737 MAX sits outside the hangar during a media tour of the Boeing 737 MAX at the Boeing plant in Renton, Washington December 8, 2015. REUTERS/Matt Mills McKnight

A Boeing 737 MAX sits outside the hangar during a media tour of the Boeing 737 MAX at the Boeing plant in Renton, Washington December 8, 2015. REUTERS/Matt Mills McKnight

A Boeing 737 MAX sits outside the hangar during a media tour of the Boeing 737 MAX at the Boeing plant in Renton, Washington December 8, 2015. REUTERS/Matt Mills McKnight