Though the 29,029-foot-high summit of Mount Everest was first conquered on foot by Tenzing Norgay and Edmund Hillary in 1953, it was conquered by air two decades earlier.

In April 1933, RAF squadron leader Douglas Douglas-Hamilton, otherwise known as Lord Clydesdale, led an ambitious attempt to fly over the summit of the world’s tallest mountain.

With the financial backing of philanthropist Lady Houston, the Houston Everest Expedition took off from an airstrip near Purnea, India at 8:25 a.m. on April 3, 1933.

Lord Clydesdale flew a modified Westland PV-3 biplane accompanied by Colonel Stewart Blacker. Following them in a Westland PV-6 was Flight Lieutenant David McIntyre and photographer S.R. Bonnett.

The flight would test not only the mechanical capabilities of the biplanes at dizzying altitudes, but also the endurance of the pilots in the thin and frigid air.