1922 (July 26), ''Maud'' Expedition and Attempted ''North Star'' Polar Flight by Roald Amundsen and pilot Oscar Omdal, cover from Nome (Alaska) to Philadelphia, bearing a pair of Amundsen's North Pole labels with two Washington 1c green affixed over, tied by ''North Star. Air Post'' confirmation marking, ''Maudexpeditionen'' straight line cachet in violet, VF and scarce. The Flight to the North Pole on a ''Curtiss'' airplane was planned in the summer of 1922, but did not take place due to the plane crash, Est. $300-$400 (Image)

1938 (July 10-14), Howard Hughes Record Around the World Flight, specially prepared legal sized cover, bearing US, French and Soviet Union air post adhesives, confirmation markings and NYC arrival ds, VF. Howard Hughes' Flight by Lockheed 14 took 91 hours, with stops in Paris, Moscow, Omsk, Yakutsk, Fairbanks, Minneapolis and New York, AAMC #TO1307, Est. $700-$800 (Image)

Air Post stamps. 1938, Eagle Holding Shield, 6c dark blue and carmine, center line vertical pair imperforated horizontally, nice offset on reverse, full OG, NH, VF, C.v. $300++, Est. $200-$240 (Image)

Air Post stamps. 1976, Plane, Globes and Flag, (31c), supposes to be in red blue and black, all colors omitted, bottom right corner sheet margin block of four, top right stamp with pencil shading, full OG, NH, VF and scarce multiple, PSE certificate, Est. $250-$300 (Image)

Air Post stamps. 1978, Wright Brothers, 31c+31c multi, block of four vertical se-tenant pairs and extra pair of No.C92, six stamps in the middle with black instead of blue inscription (US Airmail 31c) at bottom, full OG with minor disturbance on top pair, NH, VF and rare, Est. $500-$600 (Image)

Air Post stamps. 1978, Wright Brothers, 31c+31c multi, top margin block of four vertical se-tenant pairs with very light printing of blue, yellow and magenta offset colors, full OG, NH, VF, Est. $150-$200 (Image)

Air Post stamps. 1983, Los Angeles Olympic Games, 40c multicolored, right sheet margin imperforate se-tenant block of four, full OG, NH, VF, C.v. $650 (Image)

Air Post stamps. 1985, Trans-Pacific Air Mail, 44c multicolored, top margin vertical imperforate pair, full OG, NH, VF, C.v. $550 (Image)

Air Post stamps. 1989, 20th UPU Congress, Futuristic Mail Delivery, 45c multicolored, bottom right margin ZIP se-tenant block of four, light blue (engraved) color omitted, full OG, NH, VF, C.v. $500 (Image)

Air Post stamps. 1991, Harriet Quimby, 50c multicolored, left sheet imprint margin vertical pair imperforate horizontally, full OG, NH, VF, C.v. $800 (Image)

Zeppelin Flights. 1925 (February 20-21), Airship (Z.R.3) Los Angeles 1st Flight to Bermuda, 2 covers with Air Mail Service. New York ''Feb.20.1925'' marking in red, one has New York, NY, the other one - Varick St. NY machine date stamps of February 18, VF, Sieger #20M, Est. $150-$200 (Image)

Zeppelin Flights. 1925 (April 21-22), Airship (Z.R.3) Los Angeles Flight to Bermuda, 4 covers (2 - Roesslers') from NYC including three with Air Mail Service. New York ''Apr. 15.1925'' ds, one in addition with City Hall ''Apr. 13'' duplex, and one without any entry marking, all with Hamilton or St. George ''22.APR.25'' arrival ds, VF, Sieger #20N, var, Est. $350-$400 (Image)

Zeppelin Flights. 1925 (April 27-May 11), Airship (Z.R.3) Los Angeles 3 covers for Direct (2) and Return Flights to Puerto Rico, tied by Air Mail Service. New York ''Apr.27.1925'', one with extra Varick St. NY ''Apr.25'' machine cancel, return flight cover with normal ''May.6.1925'' date stamp of San Juan, appropriate receivers on the back, VF, Sieger #20T, U, Est. $250-$300 (Image)