National Air Transport's Contract Air Mail Route 3 was the main north and south trunk route and was expected to carry a large volume of mail. 

Under the schedules as of July 1, 1929 the Contract Air Mail Route 3 night flight planes were routed from Fort Worth via Oklahoma City and Ponca City to Wichita. The day plane flew from Fort Worth to Kansas City with a single stop at Tulsa.

This was a new directional service. 

No official cachets were provided but some covers bear distinctive markings provided by the airline or others. 

This cover was carried on the inaugural Contract Air Mail Route 3 Day flight from the Fort Worth, Texas Airport Mail Facility to Chicago, Illinois (where it was backstamped) and is listed in the Contract Air Mail Flights (CAM) section of The American Air Mail Catalogue as 3N14f.

On March 31, 1930, National Air Transport was absorbed into United Aircraft and Transport Corporation.

On July 1, 1931, Boeing formally consolidated its own system with Varney Air Lines, Stout, Pacific Air Transport, and National Air Transport to create United Air Lines.