There were two sets of airmail stamps issued, one in 1925, and then another in 1929. Take care with the 1925 set as forgeries abound, they are easy to spot, most are on white paper with a shiny appearance, also the perforation gauge is usually incorrect. Ironically the forgeries have become collectable in their own right. A wide range of flight covers can be found; most are philatelic creations rather than being genuine commercial mail. There is much written about airmails and students of these will find plenty of information available. The aeroplane was a real success in Africa as the large distances between cities, towns and villages suddenly became relatively shorter!