Utilize the input text as a context reference, choose the right relationship between Babcock International and London 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.

The chairmen of FTSE 100 engineering giant Babcock International (LSE: BAB.L - news ) , British Land (LSE: BLND.L - news ) and the AA have put their names to an open letter from Heathrow chairman Sir Nigel Rudd urging ministers to support expansion of the west London airport.

Answer: headquarters_location