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A turbine variant for the popular line of Convair twin engine transports was first tested only a few years after the initial piston 240 model first entered service for the airlines. The prototype CV-240 was sent to the Allison Division of General Motors in June of 1949 and fitted with two 501-A4 turboprops for evaluation. These would evolve into versions used for the Lockheed C-130 military transport and Electra (L-188) airliner.

Meanwhile, D. Napier and Son of England was the first company to get certification for their turbine N.El.6 "Eland" engine and leased an Eland powered Convair 340 to Allegheny Airlines in the U.S. on July 11, 1959 for in-service evaluation. Convair conversions were limited for this version known as the "540" with Allegheny operating five of the aircraft until 1962. At this time, Rolls-Royce bought Napier Engines and ceased the conversion program, but came up with another variant using their own "Dart" turbines. This line of Rolls-Royce powered Convairs began entering service in 1965 with the 240 models now called "600"s and the 340/440 conversion known as the "640".

While the British variant of the popular Convair airliner met with limited success, Allison had refined its more powerful 501 series of turboprop engines with the new airframe / engine match certified on April 21, 1960 as the "580". Convair's new line of turbojet 880s kept the company too busy to handle the conversion, so it was contracted out to PacAero of Santa Monica, California which had previous experience with the Napier 540 model. In addition to the 3750 shaft horsepower Allison turbine power plants, modification for the 580s also included a redesign of the over wing portion of the engine nacelles and exhaust area, anti-skid brakes with heavier ply tires, and enlarging the tail by 12 square feet for the vertical fin / rudder and 17 square feet to the horizontal surface due to the increased performance of the aircraft.

The first 26 airplanes off the line went to non-airline customers such as General Motors and the FAA starting in September of 1961 with Frontier being the first airline customer in 1964. Other airlines on the list included AVENSA (of Venezuela), Allegheny, Lake Central and North Central. A total of 170 Convair 340/440s were transformed into 580s with the last one (N4801C) of North Central Airlines completed at PacAero's parent unit, Pacific Airmotive in Burbank, CA on July 26, 1969.

The Convair short / medium series of "Convairliners" proved to be an extremely popular choice for many airlines and other operators from its beginnings in the late 40s and continuing today in all parts of the world, helped significantly by its transformation from a piston to a jet-powered aircraft.

Even as the first Convair 340s were being delivered from Continental Airlines in 1959, North Central was already thinking about a future upgrade to turbine power. It wasn't until 1966 that this study led to a decision to convert 20 Convair 340/440s with an option for 11 more. The first NCA Convair chosen, N4825C (CV-440 MSN#380), was sent to Pacific Airmotive in Burbank, California on October 26, 1966 and arrived back at North Central's Minneapolis/St Paul main base under jet-power on January 26, 1967.

In addition to the two powerful Allison turboprops, the 580 also incorporated an APU (auxiliary power unit). This Airesearch small jet engine was mounted in the right engine nacelle area and provided standby electric power and air pressure for air conditioning / pressurization in the air and electrical power and air for engine start and air conditioning on the ground (The first two 580's delivered, #549 and #522, initially came with a GTC or gas turbine compressor which was modified to act like an APU). North Central's maintenance department added the new corporate colors of navy, aqua and gold to the 580s exterior and interior. The cabin featured alternating aqua and gold seats with aqua and gold carpeting, beige walls and white ceilings. This theme would carry over to the Douglas DC-9-30 turbojets which were due for delivery later the same year (September '67). Cockpit modifications included a Collins autopilot, new solid state navigation / communication radios, dual flight directors, a Sperry C-9 compass system as well as controls required for the turbine engines. Unique to NCA 580s were the addition of master warning lights on the instrument panel as well as control yokes that were cut down by 3 inches to more easily see the flight instruments.

Initial training took place for the pilots at Frontier Airlines in Denver in late 1966 and for the maintenance personnel at Allison's Indianapolis training center. After N4825C arrived at Minneapolis/St Paul in January '67, the aircraft was used by North Central to train additional crews and personnel.

First jet-powered service started on the April 1, 1967 schedule with N4825C (Ship 549) and N3429 (Ship 522 - Convair 340 MSN#109) flying to Eau Claire, Wausau/Marshfield, Stevens Point/Wis Rapids, Oshkosh/Appleton, Green Bay/Clintonville, Manitowoc/Sheboygan, Madison and Milwaukee, Wisconsin; Minneapolis/St Paul, Duluth/Superior(Wis), Minnesota; Rapid City, Pierre, Aberdeen, and Watertown, South Dakota; and Chicago, Illinois.

Eventually, all 33 Convair 340/440s were converted with two additional 440s (N968N - CV440 MSN#462 and N969N - CV440 MSN#475) bought and converted before entering service. The Convairs were modified at the rate of about one per month with the last North Central airplane (N4801C) also terminating Pacific Airmotive's entire 580 conversion program on July 26, 1969.

This aircraft proved extremely beneficial for North Central as actual cost per aircraft mile dropped by 31 cents compared to the 340/440. The 580 was so efficient for North Central's system that 24 of the turboprops remained in service when NCA purchased Southern Airways in 1979 to form Republic Airlines. When Northwest bought Republic in 1986, 13 of the 580s were still in service and used through the late '80s.

Convair 580 Development

North Central Convair 580

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