Utilize the input text as a context reference, choose the right relationship between Boeing 737 and Southwest Airlines from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

WASHINGTON Aug 17 The U.S. Federal Aviation Administration (FAA) on Monday proposed a $325,000 penalty against Southwest Airlines Co for allegedly operating a Boeing 737 that was not in compliance with federal regulations.

Answer: operator