After the armistice, he became the first test pilot for the National Advisory Committee on Aeronautics at Langley Field, Virginia.

From July 1925 to mid-1927, he flew rebuilt de Havilland DH-4s as an airmail pilot for the Post Office Department over the treacherous Rocky Mountain routes between Cheyenne and Salt Lake City, sometimes under extremely adverse conditions.

Theodore von Kármán intervened and recommended the Boeing wind tunnel be designed for airspeeds near the speed of sound.

Two crewmen bailed out as the plane narrowly missed downtown Seattle skyscrapers on its southbound approach to Boeing Field, but their parachutes did not deploy in time and they were killed.

The aircraft crashed into the Frye Packing Plant just short of the runway; Allen, eight other crewmen, and 19 workers in the meat-processing factory were killed.

[3][19][20][21][22] While fighting the fire in the packing plant, a city fireman was overcome by fumes and succumbed, bringing the death toll to 29.

[22][23] On 23 April 1946, three years after Eddie Allen's death in the crash of XB-29, he was posthumously awarded the Air Medal — an honor rarely bestowed upon a civilian — by direction of the President of the United States.

On 17 December 1942, he presented the prestigious Wright Brothers lecture, "Flight Testing for Performance and Stability."

He was posthumously awarded the Daniel Guggenheim Medal in 1943, the citation for which read: "For major contributions to aeronautics leading to important advances in airplane design, flight research, and airline operation; particularly for the presentation of new methods for operational control and for the development of scientific and systematic methods in the flight testing of aircraft for basic design and performance data.