Cover with typed 'Via Aerea' underlined in red franked with strip of three 1928 1c on 2p 50c deep dull purple and 1927 1c olive green TAX issue (SG 226 & 223) tied by large CORREO AEREO GUATEMALA cds's dated in error 29 ABR 1929 (it should have been the 28th). Flown on the GUATEMALA CITY - MEXICO first flight by Pickwick Airways without any cachets. MEXICO CITY arrival cds on reverse dated 28 ABR 1929. A very rare flight. (Muller #11 rated 2500pts, Goodman #AM13)