Heathrow Airport is London's principal international airport. The site entered civil use as London Airport in 1946 and developed into a major global passenger and cargo hub. Its two runways are the northern 09L/27R (3,902 m) and southern 09R/27L (3,658 m). The runway-length field records the longer northern runway. Source: Heathrow operator FAQs, https://www.heathrow.com/company/about-heathrow/company-faqs (accessed 17 October 2026).