According to Official Guinness Records,
On 3 April 1933, two aircraft, a Houston-Westland and a Westland-Wallace - both open cockpit bi-planes fitted with Bristol Pegasus SIII engines - made the first manned flights over Mount Everest (29,035feet), the highest mountain in the world. The aircraft took off from Lalbalu aerodrome, near Purnea, India crewed by Colonel LVS Blacker and Squadron Leader the Lord Clydesdale in one and Flight Lieutenant DF MacIntyre and Mr SR Bonnet in the other. The flight took three hours, covered a return distance of 320 miles reaching nearly 30,000 feet clearing the mountain by a reported 100 feet. Close range photographs of Mt Everest proved the achievement.
For a complete list of 1933 records, please visit 1933 Guinness Records in India.