COLLECTIBLE: INDIA, 1926, Sept. 21, Cobham Return Flight, Calcutta-Allahabad Flight. India 3p block of four, cancelled by Calcutta Sept. 20, 1926 double-circle datestamp on cover to Naini (Aallahabad), printed label at top left regarding flight, times and cause for delay, additionally affixed with ½a pair tied by Allahabad double-circle datestamps on reverse (needed to be re-posted) and Naini arrival backstamp, Very Fine, only twelve covers are believed to have been carried on this flight, signed Stephen Smith on reverse, illustrated on pg. 95 of Indian Airmails: Development and Operations, 1911-1942 by Pradip Jain