Air Mail cover 1925 (16 Nov.) Imperial Airways Survey Flight by Sir Alan Cobham, an envelope annotated "London-Cape Town Air Survey/Mongalla 1926" and bearing Sudan 10m. adhesive cancelled at Mongalla (9.1.1926), reverse showing "KHARTOUM" (23.1) transit c.d.s., addressed to London though showing no arrival c.d.s.; signed by the flight engineer Arthur Elliott. A recent discovery which is thought to be unique. Photo