If you've been on one Southwest Airlines plane, in a way, you've been on them all. Since the company's inception, the strategy has been to keep costs down by flying only one plane model: the Boeing 737. This was thought to keep maintenance costs down. But the problems with the newest generation of the 737 have caused industry analysts to ask some tough questions about the future of the partnership.

Can Southwest still bet on the reliability of the 737 even as the new 737 MAX jets are grounded around the world? CNBC investigates.