North Central Airlines added Baltimore to its network on August 1, 1978.

Most collector covers sent to the Detroit Airport Mail Facility were postmarked with an August 1, 1978 Airport Mail Facility hand cancel, such covers were not dispatched to the Air Mail Route 86 inaugural flight to Baltimore and were instead placed in the normal mailstream.

A nondominated "A" stamp paid the postage fee.

Effective July 1, 1979, the Civil Aeronautics Board approved the merger of Southern Airways and North Central Airlines. The merged companies became Republic Airlines, Inc.

On January 23, 1986, Northwest Airlines announced the biggest merger in U.S. civil aviation history to that date — an $884 million purchase of Republic Airlines. The two carriers filed a merger application with the Department of Transportation on January 27. The Justice Department opposed the merger because it would “substantially lessen competition” in violation of antitrust laws. Full hearings regarding the merger were held and on July 31 the Department of Transportation approved Northwest Airlines’ takeover of Republic Airlines. On August 12 the acquisition of Republic was completed as officials from both airlines transferred ownership of Republic to Northwest. On October 1, 1986, Republic's operations were fully integrated into a single Northwest flight schedule.