No. 39 of the year 1931 As the result of failures of main‐plane ribs to Drawings Nos. F. 1293 and 1295, in Avian aircraft, such ribs must either be modified in accordance with Messrs. A. V. Roe & Co.'s Modification No. Avian/95 or replaced by the latest type of Avian rib to Drawings F. 1621 and F. 1644.
(1931), "Air Ministry Official Notices: Instructions to Aircraft Owners and Ground Engineers Regarding Essential Modifications", Aircraft Engineering and Aerospace Technology, Vol. 3 No. 11, pp. 293-294. https://doi.org/10.1108/eb029476
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