1929-1931 WILSON AIRWAYS COVERS: Quartet inc. v. scarce 1929 unfranked env. intended to be flown on 25 Oct Wilson Airways 'Knight of the Grail' flight London to Nairobi but against regulations to carry mail so returned to sender [one of only 20 such covers & numbered '10' in bottom left corner], 1931 (8 July) 20c p.stat env franked 15c tied Nairobi cds via FF Nairobi-Kisumu feeder service & signed 'N. J. N. Mostert Pilot/Wilson Airways Ltd.'', etc. (4 covers) Cross Reference : AIR MAIL COVERS (Image)