The Merlin series of turboprop executive transports was Swearingen's first manufacturing program, and laid the foundations for the successful Metro series of commuters.
The Merlin IV designation applies to corporate configured versions of the Metro series of commuter airliners. The Merlin designation covers the corporate versions of the original Metro II (which used a stretched Merlin II's fuselage coupled with a new wing, undercarriage and tail), the IVB is the executive equivalent of the Metro III.
As a "corporate" Metro firm "Swearingen" suggested plane SA-226AT Merlin IVA , delivery of which began in 1970. Different plane fuselage with a reduced number of windows (two on each side), can accommodate 12-15 passengers in the presence of the luggage compartment and toilets.
Corporate version of Metro III, Merlin IVC, among other improvements, was equipped with a cockpit instrumentation Bendix.
In 1979, "Swearingen" became part of the group "Fairchild Industries", becoming "Fairchild Aircraft Corporation", but retained its headquarters in San Antonio.