• 1900 – The Wright brothers arrive at Kitty Hawk, North Carolina, to begin their first season of glider experiments there
• 1908 – Seeking a contract to build the United States Army’s first airplane, Orville Wright begins flight trials before Army observers at Fort Myer, Virginia, in a new Wright Model A flyer. The flight lasts 1 min 11 seconds.
• 1908 – Goupy No.1, is the world’s first triplane. The French Goupy, was built by Ambroise Goupy, it has three sets of wings; each stacked above the others and is powered by 50-hp Renault engine.
• 1910 – Bessica Raiche makes the first solo airplane flight by a woman in the United States to be accredited at the time by the Aeronautical Society of America.
• 1911 – The first US airmail flight is made. Earle Ovington flies 9.7 km (6 miles) from Nassau Boulevard, New York to Mineola, New York.
• 1923 – First flight of the Handley Page Type S
• 1930 – The first nonstop airplane flight from Europe to the United States was completed in 37 hours as Capt. Dieudonne Costes and Maurice Bellonte of France arrived in Valley Stream, N. Y., aboard a Breguet biplane. (The plane was known as “The Question Mark” because it bore the image of the punctuation sign on its side.)
• 1939 – Germany invades Poland. The Luftwaffe plays a key tactical bombing role in neutralising Polish defences.
• 1940 – Adolf Hitler orders German bombing attacks on London.
• 1942 – First flight of the Boeing B-29 Superfortress
• 1974 – The U. S. Air Force SR-71 Blackbird 61-17972, flown by Major James Sullivan (pilot) and Major Noel F, Widdifield (reconnaissance systems officer), crosses the Atlantic Ocean from New York City to London in a world record 1 h 54 min 56 seconds at an average speed of 1,806.96 mph (2,909.76 km/h).
• 1974 – Introduction of the Grumman F-14 Tomcat
• 1983 – Korean Air Lines Flight 007, a Boeing 747, is shot down by Soviet fighter planes near Sakhalin and Moneron Island after straying into Soviet airspace; all 269 people on board are killed.
• 2004 – The Burt Rutan Ansari X Prize entry SpaceShipOne performed a successful spaceflight, the first of two needed to win the prize.
• 2011 – 2011 Reno Air Races crash: The North American P-51D Mustang The Galloping Ghost, flown by James K. “Jimmy” Leeward, crashes into box seats in front of the grandstand at the Reno Air Races at Reno Stead Airport north of Reno, Nevada. Leeward and 10 others are killed and 69 people are injured. It is the third-deadliest airshow accident in U.S. history and the deadliest aviation accident of any kind in the United States in two years.
• 2011 – Boeing delivers its first Boeing 787 Dreamliner to a customer, All Nippon Airways, at Paine Field in Washington.^[1]

.

The above list is a subset of the aviation events and milestones that took place in the month of September.  A more complete list can be found on this Wikipedia page.