Post Office Department airmail pilots never carried U.S. airmail stamped envelopes. The first U.S. air post stamped envelopes became available to the public on January 12, 1929. These stamped envelopes carried the red and blue border design that marked U.S. airmail stationery for most of the 20th century.
Here are some examples of U.S. airmail stamped envelopes.
Issued June 28, 1971
Issued May 21, 1947
Issued May 2, 1956
First day of use stamped envelope issued on May 21, 1947.
Issued September 26, 1932
Issued September 26, 1946