07/31/2016. Remarks by Johan Visschedijk: "The Model 340 had reached the market at a time of transition from piston-engines to turboprops and it was an ideal candidate for upgrading. Over a long period, Convair had been working with General Motors' Allison Division on turboprop power for the Convair-Liner. The Allison YT-56 was first installed in a pair of Convair 340s which became YC-131Cs and the Allison 501, which was the civil version of the T-56 provided the basis for the Convair 580. At about the same time Convair also pursued installation of the Rolls-Royce Dart 542-4 which resulted in the Convair 600 (based on the Convair 240) and the Convair 640 (based on the Convair 340 and 440).
In the end, 33 Convair 240s became Convair 600s. 183 Convair 340s and 440s were converted to turboprop power. This represented over 55% of the later series civil aircraft built (excluding write-offs) and demonstrated how satisfactory the Convair-Liner was as a regional turboprop airliner in the market which became dominated by the Fokker F-27. The majority, a total of 155 airframes, became Convair 580s (97 converted from Convair 340s and 58 from Convair 440s) and 27 became Convair 640s (nineteen based on '340 airframes and eight using '440 airframes). In addition, Convair delivered three late model 440s to Canadair for completion as Canadair 540s and Canadair also built seven new aircraft for the RCAF which were subsequently converted to Convair 580 standard.
The pictured aircraft was built on September 20, 1948, and delivered to American Airlines on the following September 30. It was named Birmingham, later renamed Hoosier State. It was sold to Trans-Texas Airways (renamed Texas International Airlines in 1969) on April 20, 1961. On March 23, 1966 it was converted to a Convair 600. The HHH on the nose stands for Hubert H. Humphrey as he used it as his campaign aircraft when he ran for democratic president candidate in 1972."