Rockwell Twin Commander


Aero Design and Engineering formed in 1950 out of the dreams of Ted Smith (previous project engineer at the Douglas Aircraft Company) and a group of fourteen engineers who pooled their skills, resources and imagination to realize their dream of building an aircraft designed especially for business use. The first production plane rolled off the line at Tulakes Airport in Oklahoma in 1951 and was designated the Aero Commander Model 520.

In 1954 the improved models 560 and 560A appeared - which were so successful that the USAF selected the Aero Commander for the use of President Dwight D. Eisenhower - marking the first use of any light twin-engined aircraft considered safe enough for the President of the United States. The Air Force ordered fifteen Aero Commanders of which two were placed in service for White House use.

Next followed the Model 680 (certified December 1955) which was created by changing the engines to Lycoming GSO-480-A1A6 engines.

Early in 1958, Aero Design and Engineering pioneered the first pressurized business aircraft. Using the newer Lycoming GSO-480-B1A6 engines, the aircraft was designated Model 720 Alti-Cruiser and also introduced the use of a 32" wing tip extension. That success brought the company to the attention of Colonel Rockwell, who acquired the company as a wholly owned subsidiary - thereby making available greatly increased resources for further development and expansion. The effect of that was the adoption of fuel injection engines and the re-design of the nacelles to reduce frontal area and drag, while at the same time substantially increasing power and performance.

The company has never had a model year. Rather, whenever aerodynamic, power plant or other technological or engineering advancements could be made, they were incorporated into current model aircraft as they became available. If the nature of the change was sufficient to require re-certification of the aircraft by the FAA, then the model number would be changed.

1960 saw the company renamed as Aero Commander, Inc and this was followed by four new models - the 500A, 500B, 560F and 680F.

In 1963 the Grand Commander was certified. The following year the first production Jet Commander 1121 flew and two months later - on December 31st, 1964 - occurred the first flight of the Turbo Commander.


Evolution History

Part I

The following information traces the evolution of the Aero Commander aircraft from the original prototype (L-3805) thru the Model 681. All information, unless referenced otherwise, was obtained from drawing effectivity, TIA and/or Model Specifications 6A1 and 2A4.

- WING DRAWING 5170000 -

1. Model L- 3805 (6A1)

L-3805 was certified on June 30, 1950, as a normal category, 4600 pound gross weight aircraft. It was powered by two Lycoming 0-435-A engines. This aircraft never went into production and only one (1) was built. Now on display in front of Aero Commander- Bethany plant.

2. Model 520 (6A1)

The 520 was first certified on January 31, 1952. It was very simular to the L-3805 except for an increase in gross weight from 4600 pounds to 5500 pounds and the engines were changed to Lycoming GO-435-C2B. In 1954 the gross weight was increased to 5700 pounds. Some structural changes were required.

3. Model 560 (6A1)

The Model 560 was certified on May 28, 1954. This model is similar to the Model 520. The following alterations were incorporated;

Gross weight increased to 6000 pounds.
Lycoming GO-480-B engines were used.
Swept vertical stabilizer was installed.
Structural modifications to the wing, landing gear, fuselage, vertical tail, and primary controls.
- WING DRAWING 5170023 -

4. Model 560A (6A1)

The Model 560A was certified to CAR 3 Amendment 12 on July 1, 1955. This Model is like the Model 560 except for the following:

Engine changed to Lycoming GO-480-C1B6 with dry sump and side mounted accessories.

Nacelles were redesigned.
Fuselage was lengthened.
Takeoff power was increased.
Structural changes to the wing, and new landing gear.
In 1956 the engines were changed to Lycoming GO-480-G1B6.

5. Model 680 (2A4)

The Model 680 was certified to CAR 3 Amendment 12 on December 14, 1955. This model was created by changing the Model 560A by increasing the gross weight to 7000 pounds and changing the engines to Lycoming GSO-480-A1A6 engines. In 1957 the engines were changed to Lycoming GSO-480-B1A6.


6. Model 560E (6A1)

The Model 560E was certified on February 21, 1957, under the following certification basis: CAR 3, November 1, 1945, Amendment 12, May 18, 1954, and 3.431, May 15, 1956. This aircraft is the same as the Model 560A except for the 32-inch wing extension added to the tips and the increase in gross weight from 6000 pounds to 6500 pounds. The engines were later changed from Lycoming GO-480-C1B6 to Lycoming GO-480-G1B6.

From Aero Commander Report 560E-L1, page 1, the following is noted, "The Model 560E is identical to the Model 680 except for the power plant and the 32-inch wing tip extension".

7. Model 680E (2A4)

The Model 680 was modified as follows to obtain the 680E.

Increased gross weight to 7500 pounds.
Added 32-inch tip extension to wing.
This model was certified on June 19, 1958, to CAR 3 Amendment 12.

8. Model 720 (2A4)

The model 720 is a pressurized model 680E. This model was certified on December 5, 1958. Also same as Model 680 except for increased weight, extended wing, pressurized cabin, and some fuselage changes.

9. Model 500 (6A1)

The Model 500 is a 6000 pound gross weight normal category airplane using Lycoming 0-540-A1A6 engines rated at 230 HP at 2575 RPM. The aircraft configuration is basically identical structurally and aerodynamically to the Model 560E. The only structural change is the Dyna-focal engine mounts which were required when the engine was changed from Lycoming GO-480-C1B6 to Lycoming 0-540-A2B. These new engine mounts were substantiated by static test and the landing gear was certified for the Model 560A. All other structure already substantiated to 7500 pound gross weight and a load factor of +3.5. (Reference Report S10-027). This model was certified on July 24, 1958.

- WING DRAWING 5170045 -

10. Model 500A (6A1)

The Model 500A is the same as the Model 500 with the following exceptions:

Wing structure modification in nacelle area.
Fuel injection engines (Continental IO-470-M).
Hydraulic systems modification.
Redesign of Cowling and nacelle.
New landing gear.
Gross weight increased from 6000 to 6250 pounds as a follow-on program.
This model was certified on April 7, 1960.

11. Model 500B (6A1)

The Model 500B is the same as the Model 500A except the gross weight changed from 6250 to 6750 pounds and the engines were changed from Continental IO-470-M to Lycoming IO-540-B1A5. The pilot entrance door was added as an option. Certification date was July 13, 1960.

12. Model 680F (2A4)

This model is the same as the Model 680E except for:

Gross weight increased to 8000 pounds.
Lycoming IGSO-540-B1A engines.
Redesigned nacelle and main gear.
The 680F was certified on August 23, 1960, per CAR 3, May 15, 1956, Amendments 3-3 and 3 4.

13. Model 680FP (2A4)

This is a pressurized 680F and as such is identical to the 680F except for cabin pressurization and modification in accordance with Aero Commander Drawing 6100021, Change A. Certified in 1961, per CAR 3, May 15, 1956, Amendments 3-1 thru 3-4.

14. Model 560F

This model is the same as the 680F except:

Gross weight reduced to 7500 pounds.
Lycoming IGO-540-B1A engines.
Certified on February 8, 1961, per CAR 3, May 15, 1956, Amendment 3-3 and 3-4.

- MODIFIED 5170045 FOR "8500-LB" WING -

15. Model 500U (6A1)

The Model 500U was certified as a utility category airplane on December 11, 1964. Except for the Utility Category, the only difference from the 500B was installation of the "8500-LB" wing.

16. Model 500S (6A1)

The Model 500S is identical structurally, aerodynamically, and has the same performance characteristics as the 500U. The only differences are as follows:

Cabin heater concept.
Baggage compartment certified for 500 pounds instead of 350 pounds.
Pilot entrance door now standard.
No new loads reports were prepared for this model. Certification was obtained on March 15, 1968, under the same basis as the 500U.


17. Model 680FL (2A4)

The Model 680FL was certified on May 24, 1963, per CAR 3, May 15, 1956, Amendments 3-3 and 3-4. This aircraft is identical to the Model 680F except for a lengthened fuselage. A 44-inch section was added forward of the front spar and 30-inches aft of the front spar. The horizontal was extended.

Later in 1963 the C.G. travel was changed to allow 10% MAC at 7000 pounds for the forward C.G.

In 1964 the gross weight was increased to 8500 pounds.

18. Model 680FLP (2A4)

This model was certified on October 8, 1964, per CAR 3, May 15, 1956, Amendments 3-3 and 3 4. The 680FLP is a pressurized version of the 680FL and is identical structurally and aerodynamically to the 8500 pound 680FL.


19. Model 680T (2A4)

The Model 680T was originally certified on September 15, 1965, per CAR 3, May 15, 1956, Amendments 3-2, 3-3, 3-4, 3-6, 3.197, 3.395, 3.396 and Special Conditions. At this time it was an 8500 pound aircraft identical to the 680FL with the following exceptions:

AiResearch engines Model TPE-331-29A.
Revised fuel system.
Pressurized to 4 psi.
Revised air design speeds.
In 1966 the 680T was recertified with the following changes:

Gross weight increased to 8950 pounds.
The 32-inch wing tip extension was removed.
Increased takeoff power.
New Propellers.
Increase of operating limits.
Airframe configuration changes, resulting in changes in flight characteristics.
At 8500 pound gross weight, 680T aircraft was reworked to this new configuration.

20. Model 680V (2A4)

The 680V was certified on June 13,1967, to the same certification basis as the 680T. The primary difference between the 680V and the 680T is the increased gross weight to 9400 pounds. The 680T with the following configuration changes define the 680V.

Structural requirements due to gross weight increase.
Contoured radome nose.
Fuel flow system with totalizer.
Picture windows.
Clam shell landing gear doors.
Fuel vent heaters.
Improved soundproofing.
Loads and stress substantiation reports refer to this model as the 9400 pound 680T.

21. Model 680W (2A4)

The Model 680W is identical to the previous Models 680T and 680V in weight, C.G. range, aerodynamic certification, and engine performance; therefore, there is no formal TIA for the 680W. The basic difference between the 680W and 680V is the change to the TPE 331-43BL engine. Certification was obtained on February 5, 1968, under the same basis as the 680T. Loads and stress substantiation reports refer to this model as the "9400-LB" 680T.

22. Model 681 (2A4)

This model was certified on March 20, 1969, under the same basis as the 680T. The 681 is identical to the 680W except for the pressurization equipment. The 681 utilizes an engine bleed air pressurization system instead of hydraulic. The loads and stress substantiation reports refer to this model as the "9400-LB" 680T.


1. The one-piece or else the laminated external wing reinforcing straps are effective on all aircraft up through S/N 1724. This effectivity is covered by production drawings and/or AD 65 6 1. The internal reinforcing strap is effective on aircraft S/N 1725 and Subs.

2. The following is offered as further clarification of the various Turbo-prop models. The gross weight of the 680T is 8950 pounds; and when modified to 9400 pounds, it becomes a 680V. All 680T and 680V aircraft have the external wing strap. The 680W is a 9400 pound Turbo-prop aircraft which has the internal strap except for the first three (S/N 1721, 22, 23) which have the external strap. The 680V and 680W are identical structurally except for the wing lights and strap configuration.

3. Model specification No. 6A1 was originally obtained for Model L-3805 and was revised to cover succeeding models until the high altitude supercharged engines were introduced. At that time a new model specification (No. 2A4) was obtained. All models, with one exception, that are covered by Spec. No. 2A4 are either supercharged or have turbo-prop engines. The lone exception is the Model 560F. The 560F is on this specification because, except for non-supercharged engines, it is like the 680F.

Part II

The previous aircraft evolution chart includes Twin Commander models up to the 681. This document continues on from that point to include the last ten models produced by Rockwell and Gulfstream. All models included on this sheet are approved under FAA Type Certificate Number 2A4 except for the Model 700.

1. Model 690

Certified July 19, 1971. Similar to Model 681. Changes include:

a) Gross weight increase to 9,850 lbs.
b) Wing length increased 30 inches at center wing section.
c) AiResearch TPE331-5-251K engines.
d) Increased rudder area.
e) Increased baggage capacity to 600 lbs.

2. Model 685

Certified September 17, 1971. Similar to 690. Primary difference is the 685 is a piston powered aircraft, using two Continental GTSIO-520 engines with non-reversing Hartzell propellers. Gross weight was decreased to 9,000 lbs.

3. Model 690A

Certified April 25, 1973. Similar to 690. Major differences are:

a) Max. altitude increased from 25,000 to 31,000.
b) Enlarged dorsal fin and longer tail cone.
c) Increased cabin pressure differential from 4.2 to 5.25 psi.
d) Heated windshield added.
e) Wing and empennage de-ice equipment became standard.

4. Model 690B

Certified October 5, 1976. Similar to 690A except for the following changes:

a) Increased ramp, take off and landing weights
b) Lead-acid batteries installed.
c) Maximum seating increased to 10.
d) Pitot heat added.
e) Various interior changes.

5. Model 700

Certified October 28, 1977 under Type Certificate Number A12SW. This was the only low wing Twin Commander model built. It was powered by two Lycoming TIO-540-R3AD engines and seated seven. Built under license by Fuji Industries of Japan.

6. Model 690C

Certified September 7, 1979. Similar to the 690B, but several changes were made. The most notable changes were:

a) 30 inch wing tip extensions added.
b) Increased seating from 10 to 11
c) Zero fuel weight reduced from 8750 to 8463 lbs.
d) AiResearch TPE331-5-254K engines.
e) Dowty Rotol propellers.
f) Engines canted down 2 .
g) Wet wing outboard of the nacelles added.
h) Fuel capacity increased from 384 to 425 gallons.
i) Nacelles redesigned.
j) Landing/recognition lights were added to the nose.
k) Extended baggage compartment floor.
l) Canted wing tips added.

7. Model 695

Certified November 1, 1979. Same as Model 690C except AiResearch TPE331-10-501K engines were used.

8. Model 690D

Certified December 2, 1981. Similar to the 690C. Differences include:

a) Increased ramp, take off, landing and zero fuel weights.
b) Increased fuel capacity from 425 to 430 gallons.
c) Higher certified altitude.
d) Increased design speeds.
e) Redesigned fuselage.

9. Model 695A

Certified April 30, 1981. Same as the 690D except AiResearch TPE331-10-501K engines were used.

10. Model 695B

Certified February 15, 1984. Same as the Model 695A except for the following:

a) Maximum ramp weight increased from 11,250 to 11,800 lbs.
b) Maximum zero fuel weight increased from 9,000 to 9,800 lbs.
c) Maximum take off and landing weights increased.
d) Structural changes to accommodate the increased loads.
e) AiResearch TPE331-10-511K engines.