Convair 240-640

Convair 440 CS-TML lifts off from its British Coventry base in the colour scheme of Atlantic Airlines.
The success of the DC3 in commercial service before the Second World War focused airlines and manufacturers on a replacement for when peacetime returned.
American Airlines issued one such requirement in early 1945 for an airliner suitable for use on routes up to 1,000 miles and Convair's talks with the company led to it building its first commercial aircraft, the 110.
Little remembered today, the 110 was the forerunner of a highly successful family of twin-propeller airliners that would dominate the 1950s and come closest to filling that most elusive of niches - the DC3 replacement.
But by the time the 30-passenger 110 had lifted off from San Diego on July 8, 1946, American had already settled on a larger, 40-seat design and ordered 75 Convair 240s. No prototype was built and the first aircraft took off for the first time on March 16, 1947, entering service with American in June 1948.
The large number of war-surplus C-47s kept sales figures down but airlines ordered 176 and another 39 were built for other customers, mainly the USAF as the C-131 transport and T-29 trainer.
An improved 340 model first flew on October 5, 1951, featuring a fuselage stretched by 4ft 6ins, larger wing and uprated Pratt and Whitney R-2800 engines. The 44-passenger 340 was also well-received, with 212 bought by airlines and 99 by other customers.
Convair did not rest on its laurels and flew the 440 on October 6, 1955. The type was basically similar to the 340 but featured redesigned engine nacelles and other refinements. The addition of radar lengthened the nose by 2ft 4ins. Eventually the type carried 52 passengers in a high density layout.
Production of the 440 reached 153 for airlines plus another 26 for other customers. The Metropolitan name was used by several European customers, including Swissair.
More than 230 of the three early models were eventually converted to turboprop power in three programmes between 1955 and 1967.
Convair first tested the possibility with a 240 flying with Allison engines on December 29, 1950, but the first attempt for airline use came from the British Napier company in 1955 when it flew a Napier engined 340. Six were converted for Allegheny as the 540 but after production of the Eland was terminated in 1962 the aircraft reverted to their earlier piston engines. Canadair also built ten 540s as CL-66B Cosmopolitans for the Royal Canadian Air Force and converted three others.
The next conversion emerged as the Allison-Convair, which became the Super Convair and then the 580. This featured Allison 501-D13 turboprops converted by Pacific Airmotive and first flew on January 19, 1960.
A total of 130 aircraft were converted, 110 for airline use, with Allegheny, Lake Central and Frontier major users.
The final conversion used the Rolls-Royce Dart 542 and was carried out by the Convair Division of Genral Dynamics, either as kits or converted airframes. Converted 240s became 240Ds and later 600s, while 340s and 440s became 640s. The first aircraft for Central Airlines first flew on May 20, 1965. Thirty-nine 600s and 28 640s were converted.
Many 580s and a smaller number of the piston marques were still in service around the world well into the 21st Century. Among these, Nolinor was the largest operator of the passenger version. Kelowna Flightcraft, also of Canada, stretched the 580 to create the 5800 and a handful have flown so far.

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