He left from Brussels (presumably from Haren Airport as the present national airport would only be created in 1940 at Melsbroek, its Zaventem terminal dating from 1956) on 12 February 1925, with mechanic Joseph "Jef" de Bruycker and co-pilot Léopold Roger, heading for N'Dolo airfield at Leopoldville (now Kinshasa). Thieffry himself acted as navigator. The flight plan called for stops at Marseille, Oran, Colomb-Bechar, Gao, Fort-Lamy, Bangui and Coquilhatville, and should have taken seven days. However strong adverse winds and a broken propeller meant that it took 51 days. Finally on 3 April, after 8,200 kilometres, they arrived at Leopoldville. The first air connection was made, and Thieffry returned to a hero's welcome in Belgium.