The 520 led to the 500, 560 and 680 series of light twins. All four were variants on each other with different engines, weights and fuel loads. In 1964, the 65, 500A, 500B, 560F and 680F Commander models were dropped in favor of the improved 500U. With a minor change, the 500U became the 500S and was also known as the Shrike Commander.
The 680FL was the precursor to the turbine-powered Commanders. Two 380 hp supercharged Lycomings power the 680FL. It also has a longer fuselage over the 500 series. From 1963 to 1969, 137 of the 680FL were built. The 680FL was also built in a pressurized version called the 680FLP.
In 1991, an airworthiness directive related to the wing spars almost drove the Twin Commanders out of existence, but support from the current certificate holder, Twin Commander Aircraft, ensured a long future ahead for the aircraft.
