The largest building within the Heathrow Terminal 5 complex is Terminal 5A, the main terminal building. This massive structure is one of the largest free-standing buildings in the United Kingdom, designed by the architectural firm Rogers Stirk Harbour + Partners. It spans 396 meters in length, 176 meters in width, and stands 40 meters tall. The building is famous for its vast, open-plan interior, which was made possible by a wave-like steel roof supported by only 22 massive steel columns, eliminating the need for internal load-bearing walls. T5A serves as the primary gateway for British Airways and Iberia, housing the majority of check-in desks, security zones, and a vast array of high-end retail and dining options. While Terminal 5 also includes two satellite buildings (T5B and T5C), they are significantly smaller and primarily serve as departure gates linked to T5A by an underground automated people mover. In 2026, T5A continues to be a landmark of modern aviation infrastructure, capable of handling tens of millions of passengers annually within its airy, glass-walled halls.