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 200-mph, seven-seat Aero Commander 520. An improved version, the 500S, manufactured after 1967, is known as the Shrike Commander. Larger variants are known by numerous model names and designations, ranging up to the 330-mph, 11-seat Model 695B/Jetprop 1000B turboprop.

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 throughout 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 it, to instead 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 rating of 520 horsepower. The production model was named the Commander 520. The first Commander 520 was rolled out of the new factory in August 1951. Serial number 1 was used as a 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, World War II pilot R. A. "Bob" Hoover demonstrated the Shrike Commander 500S for decades in a variety of "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 D. 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 unpressurized, long-fuselage 680FL was operated as a small package freighter by Combs Freightair in the 1970s and 1980s, and by Suburban Air Freight in the 1980s and 1990s. The aircraft was popular with pilots, because it was extremely "pilot friendly" and with its 380 hp supercharged engines did well in icing meteorological conditions. A number are still operated on contracts for cargo and fire control applications, as their piston engines offer good fuel specifics at low altitudes and longer loiter times.

Safety concerns

Single-engine safety

Single-engine flight to Washington
In 1950, when the developers were working to satisfy Civil Aeronautics Authority 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.
However, the stunt had been performed with the propeller stowed inside the aircraft, rather than dragging in the open on the front of the engine. Consequently, the famous demonstration did not demonstrate an actual failed-engine scenario.
NTSB Single-engine safety study
In 1979, the National Transportation Safety Board reviewed light-twin engine-failure accidents, involving the 24 most popular model-groups of light twins between 1972 and 1976. They found that the piston-engined twin-Commanders had averaged slightly over 3.4 engine-failure accidents per hundred-thousand hours, the second worst number of all aircraft under review. The most engine failures were suffered by the small-engine versions of the Piper Apache, at 6.9 failures per hundred thousand hours; the third-worst, the Beechcraft Travel Air, averaged 2.9 failures; the average for all models was only 1.6.
Hoover single-engine airshow routine
Countering the statistical evidence, Rockwell demonstration pilot Bob Hoover's famous airshow stunt routine, with the Shrike Commander, included a full aerobatic routine performed first with both engines, then with one engine out, then both engines out, and gliding. Then in his final airshow performance, in a supreme demonstration of conservation of momentum, he did all that, then landed the Shrike Commander dead stick, coasted the airplane down the runway then from the runway down the taxiway and silently let the craft roll slowly to a full stop right in front of the crowd.
Turboprop Commanders' single-engine safety
The turboprop twin-Commanders—with much more powerful engines – came out on the opposite end of the rankings, with one of the lowest rates of engine-failure accidents of all "light" twins examined, at only 0.4 per hundred-thousand hours.

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 to 1993, 24 aircraft crashed when spar failures caused the loss of the wing in flight. Thirty-five more spars were found cracked during inspections.

Notable accidents

;Aero Commander L.3805: Prototype, one built, Lycoming O-435-A engines.
;Aero Commander 520: First production version, a developed L.3805 with a 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 takeoff weight, seven seats and more powerful engines, 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.
;: 500A 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 500S/Shrike Commander: 500U with minor changes, 316 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 takeoff 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.
;: Built for the National Oceanic and Atmospheric Administration.
;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.
;: 690 powered by two 435 hp Continental GTSIO-520K piston engines, 66 built.
;: 681 with new wing centre section and engines moved further outboard, two Garrett AiResearch TPE331-5-251K turboprops, 79 built.
;: 690 with changed flightdeck layout and increased pressurisation, 245 built.
;: 690A with improved soundproofing and internal lavatory, 217 built.
; Jetprop 840: 690B with increased wingspan, wet wing fuel tanks and winglets, two 840shp TPE331-5-254K turboprops, 136 built.
;690D Jetprop 900: 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 takeoff 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, two built.
;NL-26D → NU-9D: One built.

Operators

Military operators

; Kingdom of Laos