Collecting US Airmail Rate covers
Since the US government began a special airmail service in 1918, there have been scores of changes reflecting the rising cost of airmail, efforts to get more use of airmail service or additive airmail services. The first US airmail stamp included the price of special delivery to first destination addressees. Then, in 1925 2c was added to pay for overnight service between Chicago and New York City; a rate which lasted until the end of US Government airmail service on January 31, 1927. The USPS eliminated airmail letter rates in 1976, with the proviso that first class letter mail would now travel by the fastest method possible, but not less than the speed of airmail if it was available. The USPS stopped issuing airmail stamps with that directive.
Collectors approach airmail rates in two major ways. The easiest and most prevalent method is to collect the first and last usage of each new rate, properly franked and routed. US Government covers from May 15th, 1918, include C-3 franked covers from New York, Philadelphia and Washington DC. Other franking adding to 24c might also be included, but the last date for 24c rate was July 13, 1918. Collectors, Dealers and Cover preparers began to focus on first day usage by providing private inscriptions, rubber stamped cachets and specially printed envelopes to dress up airmail rate change letters. The second, more difficult method, would be collections of covers mailed, franked and routed with proper rates during their period of validity. Commercial covers flown over the CAM 8 routes franked with the 10c Map stamp are quite common, but letters mailed from Los Angeles to Seattle, bearing the 15c rate, especially franked with the 15c Map stamp, are scarce.
Another interesting aspect of US airmail rate collecting is the period between the February 15, 1926 and February 1, 1927. During that time the CAM route rate existed in parallel with the USG Airmail Service rate causing confusion for collectors and postal clerks. Inaugural CAM covers of routes 2,3, 4, 5,6,7, 8, 9 can be found with these integrated rates, but the confusion resulted in many covers with incorrect postage. Once again, the more difficult collection includes commercial covers, properly franked with the correct postage for the time; instead of categorized as philatelic, such covers are truly US postal history.
Lee Downer, AAMC
American Air Mail Catalogue, 5th Edition, vol. 2, pp 491-99. US Domestic Air Mail Rate Changes.
US Domestic Postal Rates, 1872-1999, Henry W Beecher and Anthony S. Wawrukiewicz
Cama Publishing Co., Portland, OR. Pp 50-62.