Belgian Congo. (Sudan - British East Africa). 1941. Air Mail envelope written from 'The Africa Inland Mission, Aba' addressed to Mombasa, Kenya bearing Belgian Congo Yvert 171, 2 5c indigo and Air Mail Yvert 5, 15f brown and black tied by Aba date stamp '7th June 41', routed via Juba (Sudan) '12th June' with British East Africa 'Opened By Censor' label with '314' censorship hand-stamp in violet and label tied by Mombasa/ Kenya receiver '14th June' on reverse.
Aba is in the Upper Congo and the cover would have crossed the Congo/ Sudan border and flown direct to Mombasa.