Aero Commander 500 family

The Aero Commander 500 family is a series of light-twin piston-engined and turboprop aircraft originally built by the Aero Design and Engineering Company in the late 1940s, renamed the Aero Commander company in 1950, and a division of Rockwell International from 1965. The initial production version was the Aero Commander 520. Piston-engined versions manufactured after 1967 are known as the Shrike Commander.

Design and development
The idea for the Commander light business twin was conceived by Ted Smith, a project engineer at the Douglas Aircraft Company. Working part-time after hours through 1944, a group of A-20 engineers formed the Aero Design and Engineering Company to design and build the proposed aircraft with a layout similar to their A-20 bomber. Originally the new company was going to build three pre-production aircraft but as the first aircraft was being built they decided to build just one prototype. The final configuration was completed in July 1946 and was designated the Model L3805.

Registered NX1946 the prototype first flew on 23 April 1948. The L3805 accommodated up to five people and was powered by two Lycoming O-435-A piston engines., it was an all-metal high-wing monoplane with retractable undercarriage using components from a Vultee BT-13 Valiant. The market segment planned for this aircraft to be sold to small feeder airliner firms and was originally designed to carry seven passengers, but instead found use in the private business aircraft and military market. Walter Beech test flew the aircraft in 1949 and expressed interest in buying the project, but passed on to develop the Beechcraft Twin Bonanza, Fairchild Aircraft also evaluated the prototype at its Hagerstown, Maryland headquarters.

The prototype flew successfully and the company leased at no cost a new 26,000 square foot factory at Bethany near Oklahoma City to build a production version certified on 30 June 1950. Nearly 10,000 hours of redesign work went into the model including more powerful Lycoming GO-435-C2 engines with a combined horsepower of 520. The production model was named the Commander 520. The first Commander 520 was rolled out of the new factory in August 1951. Serial number one was used as an demonstrator then sold in October 1952 to the Asahi Shimbun Press Company of Tokyo.

Operational history
In military service, it was initially designated the L-26 though in 1962 this was changed to U-4 for the United States Air Force and U-9 for the United States Army.

Under ownership of Rockwell in the 1960s, WWII pilot Bob Hoover demonstrated the Shrike Commander 500S for decades in a variety a "managed energy" routines including single-engine and engine-out aerobatics. His Shrike Commander is displayed in the colors of his last sponsor Evergreen International Aviation at the Steven F. Udvar-Hazy Center of the Smithsonian Air and Space Museum. Bob Odegaard continued the tradition in 2012 flying a 1975 Shrike 500S in a Bob Hoover tribute routine.

One U-4B became a presidential transport aircraft for Dwight Eisenhower between 1956 and 1960. This was the smallest "Air Force One," and the first to wear the now-familiar blue-and-white livery.

As of 2004, Shrike Commanders remained in service with the United States Coast Guard and United States Customs Service.

A single 560F was operated by the Belgian Air Force as the personal transport of the late king Boudewijn from 1961 to 1973.

The non-pressurized, long-fuselage 680FL was operated as a small package freighter by Combs Freightair in the 1970s and 80s, and by Suburban Air Freight in the 1980s and 90's. The aircraft was popular with pilots because it was extremely "pilot friendly" and with its 380 hp supercharged engines did well in icing. A number are still operated on contracts for cargo and fire control applications, as their piston engines offer good fuel specifics as low altitudes, and longer loiter times.

Single engine safety
In 1950, when the developers were working to satisfy Civil Aeronautics Authority (CAA) regulations for certification of the 500, they chose a novel method of demonstrating its single-engine safety and performance: they removed one of the two-bladed propellers, secured it in the aft cabin, and flew from Bethany to Washington D.C. on one engine. There they met with CAA personnel, then replaced the propeller and returned to Oklahoma in the conventional manner. The flight received nationwide coverage in the press.

Wing spar fatigue
Beginning in June 1991, senior engineers met with FAA officials to discuss concerns over the Aero Commander's main wing spar, which was believed to be susceptible to stress fatigue and subsequent cracking, and was believed to have resulted in a number of fatal crashes. From approximately 1961–1993, 24 aircraft crashed when spar failures caused the loss of the wing in flight. 35 more spars were found cracked during inspections.

Notable accidents
World War II hero and actor Audie Murphy died in an Aero Commander 680 while flying in a thunderstorm over Roanoke, Virginia on 28 May 1971. Five others and the pilot were also killed.

On 19 June 1964, Senator Ted Kennedy was a passenger in an Aero Commander 680 airplane flying in bad weather from Washington to Massachusetts. It crashed into an apple orchard in the western Massachusetts town of Southampton on the final approach to the Barnes Municipal Airport in Westfield. The pilot and Edward Moss, one of Kennedy's aides, were killed. Kennedy suffered a severe back injury, a punctured lung, broken ribs and internal bleeding.

Variants

 * Aero Commander L.3805: Prototype, one built.
 * Aero Commander 520: First production version, a developed L.3805 with taller fin and larger cabin with two 260 hp Lycoming GO-435-C engines, 150 built.
 * Aero Commander 560: Model 520 with swept tail, increased take-off weight, seven seats and more powerful engines (two 270 hp Lycoming GO-480B engines) and refined wing, 80 built.
 * Aero Commander 560A: New undercarriage, stretched fuselage and other numerous refinements, 99 built.
 * Aero Commander 560E: Larger wings and greater payload, 93 built.
 * Aero Commander 560F: Powered with 350 hp Lycoming IGO-540 engines.
 * Aero Commander 360: Lightened version of the 560E with four seats and two 180 hp engines, one built.
 * Aero Commander 500: Economy version introduced in 1958, a 560E with 250 hp Lycoming O-540-A engines, 101 built.
 * Aero Commander 500A: First Aero Commander model – new nacelles to house 260 hp fuel-injected Continental IO-470M engines, 99 built.
 * 560E with 290 hp fuel injected Lycoming IO-540 engines, 217 built.
 * Aero Commander 500U/Shrike Commander: 500B with pointed nose and squared off tail, two 290 hp Lycoming IO-540 engines, replaced 500A, 500B, 560F and 680F, 56 built.
 * Aero Commander 680 Super: Development of 560A with supercharged 340 hp Lycoming GSO-480-A engines and increased fuel capacity, 254 built.
 * Aero Commander 680E: Lightened 560E and 560A type undercarriage, 100 built.
 * Aero Commander 680F: 680E with new undercarriage and supercharged, fuel-injected 380 hp Lycoming IGSO-540 engines and new nacelles, 126 built.
 * Aero Commander 680FP: Pressurized version modified from 680F, 26 built.
 * Aero Commander 680FL Grand Commander: 680F with stretched fuselage and larger tail, 157 built. After 1967 known as the Courser Commander.
 * Aero Commander 680FL/P Grand Commander: Pressurized version of 680FL, 37 built.
 * Aero Commander 680T Turbo Commander: 680FL/P with Garrett TPE331-43 turboprop engines, 56 built.
 * Aero Commander 680V Turbo Commander: 680T with increased take off weight and slightly improved cargo capacity, 36 built.
 * Aero Commander 680W Turbo II Commander: 680V with pointed nose. squared off fin, one panoramic and two small cabin windows and weather radar, 46 built.
 * Rockwell 681 Hawk Commander: 680W with improved pressurisation, air conditioning system and nose, 43 built.
 * Rockwell 681B Turbo Commander: Marketing designation for economy version of the 681, 29 built.
 * Rockwell 685 Commander: 690 powered by two 435 hp Continental GTSIO-520K piston engines, 66 built.
 * Commander 690: 681 with new wing centre section and engines moved further outboard, two Garrett AiResearch TPE331-5-251K turboprops, 79 built.
 * Commander 690A: 690 with changed flightdeck layout and increased pressurisation, 245 built.
 * Commander 690B: 690A with improved soundproofing and internal lavatory, 217 built.
 * Jetprop840: 690B with increased wingspan, wet wing fuel tanks and winglets, two 840shp TPE331-5-254K turboprops, 136 built.
 * 690D Jetprop900: Similar to 690C with internal rear cabin extension, improved pressurisation and five square cabin windows, 42 built.
 * 695 Jetprop 980: Similar to 690C with 735shp TPE331-10-501K engines, 84 built.
 * 695A Jetprop 1000: 690D with higher take off weight and more powerful TPE331-10-501K engines, 101 built.
 * 695B Jetprop 1000B: 695A with minor changes, 6 built.
 * Aero Commander 720 AltiCruiser: Pressurized version of 680, 13 built.
 * YL-26 → YU-9A: Aero Commander 520 evaluated by the US Army, 3 built.
 * YL-26A: Aero Commander 560 evaluated by the US Air Force, 1 built.
 * L-26B → U-4A: Aero Commander 560A sold to the US Air Force, 14 built.
 * L-26B → U-9B: Aero Commander 560A sold to the US Army, 1 built.
 * L-26C → U-4B: Aero Commander 680 Super sold to the US Air Force, 2 built.
 * L-26C → U-9C: Aero Commander 680 Super sold to the US Army, 4 built.
 * RL-26D → RU-9D: Commander 680 for US Army aircraft fitted with SLAR (side looking airborne radar), two built.
 * NL-26D → NU-9D: One built

Military operators

 * Argentine Air Force - 1 x 500B, 27 x 500U and 1 x 680
 * Argentine Army Aviation - 680V, 690A
 * 🇧🇪 Belgium
 * Belgian Air Force - 1 x 560F - served as royal transport 1961-1973
 * Benin Air Force - 1 x 500B
 * Fuerza Aerea Colombiana (690D, 695A)
 * Ejercito Nacional de Colombia (695)
 * Hellenic Army Aviation - 2 x 680FL
 * Honduran Air Force
 * Indonesian Army Aviation - 2 x 680FL
 * Iranian Islamic Revolutionary Air Force - 3 x 681B
 * Iranian Islamic Revolutionary Army Aviation - 3 x 690, 2 x 690A
 * Iranian Islamic Revolutionary Naval Aviation - 2 x 500S, 2 x 690, 6 x 690A
 * Ivory Coast Air Force - 1 x 500B
 * Kenya Air Force - 1 x 680FP (no longer operated)
 * Republic of Korea Air Force - 3 x 520, 2 x 560F
 * Mexican Air Force - 20 x 500S
 * Niger Air Force - 1 x 500B
 * Pakistan Air Force - 1 x 680E (with radar nose), 1 x 680F
 * Pakistan Army Aviation - 1 x 690B
 * Fuerza Aerea del Peru (690B)
 * $\phi$
 * Philippine Air Force - 1 x 690
 * United States Air Force as the L-26 and U-4
 * United States Army as the L-26 and U-9
 * Dominican Air Force - 1 x 680T Turbo Commander
 * Mexican Air Force - 20 x 500S
 * Niger Air Force - 1 x 500B
 * Pakistan Air Force - 1 x 680E (with radar nose), 1 x 680F
 * Pakistan Army Aviation - 1 x 690B
 * Fuerza Aerea del Peru (690B)
 * $\phi$
 * Philippine Air Force - 1 x 690
 * United States Air Force as the L-26 and U-4
 * United States Army as the L-26 and U-9
 * Dominican Air Force - 1 x 680T Turbo Commander
 * Philippine Air Force - 1 x 690
 * United States Air Force as the L-26 and U-4
 * United States Army as the L-26 and U-9
 * Dominican Air Force - 1 x 680T Turbo Commander
 * Dominican Air Force - 1 x 680T Turbo Commander
 * Dominican Air Force - 1 x 680T Turbo Commander