On Sept. 17, 1908, a modified Wright Brothers aircraft crashed during a demonstration at Fort Myer, Va., seriously injuring pilot Orville Wright and killing the observer, U.S. Army Lt. Thomas E. Selfridge. Selfridge's death was a severe blow, for through his experiments with Alexander Graham Bell, he had gained great technical knowledge and knew far more about airplanes than anyone else in the Army. On Dec. 6 1907, Selfridge had been the first Army officer to solo in a powered aircraft, the White Wing, developed by Aerial Experiment Association, of which Bell was the president. Because of the accident at Fort Myer, the War Department postponed the delivery of the Wright Brothers' machine until the following summer.
For additional information see the National Museum of the USAF.