The following article has come to the attention of our President:

Andrew Fischer, Airmail Rates of Portuguese East Africa, Asia Pacific Exhibitor, vol. 28 no. 1, pp. 61-67, May 2014.

Members can obtain a copy from our Librarian. John Cross mentioned another article, with more extensive information:

Altino Silva Pinto and Giorgio Micali, O início da VIA AÉREA e as respectivas tabelas de porte, Boletim do Clube Filatélico de Portugal no. 424, pp. 55-66, June 2009.