Rockwell Commander 685

Overview

The Rockwell Commander 685 is the rare piston-engine derivative of the Commander 690 turboprop airframe, built by Rockwell at the Bethany, Oklahoma factory and FAA type-certificated on September 17, 1971. It pairs the larger, pressurized 690 fuselage with twin 435 hp Continental GTSIO-520-F/K geared-and-turbocharged piston engines turning three-blade Hartzell feathering propellers, giving the late-Commander family its only fully pressurized piston cabin twin in the 9,000 lb gross-weight class. Production ran from 1971 through 1976 for a total of about 66 airframes.

The 685 occupied an unusual showroom slot. It was offered alongside the turbine 690 with the same cabin, the same systems philosophy, and a markedly lower acquisition cost than its turboprop sibling – but with the GTSIO-520 powerplant economics of a high-output geared turbocharged piston rather than the simpler PT6 or TPE331 turbines that increasingly defined the cabin-class market by the mid-1970s. Buyers who chose the 685 over the 690 chose acquisition price over operating simplicity; the market made the opposite choice often enough that the 685 was discontinued after five model years while the 690 series continued in production for another decade.

For a buyer evaluating one today, the 685 is a niche acquisition. The cabin and the airframe are excellent; the 690’s later refinements are largely absent because the 685 predates them; and the GTSIO-520 powerplant requires specialist support that is meaningfully harder to find than King Air PT6 or Twin Commander TPE331 support. Type-club support runs through Twin Commander Aircraft LLC alongside the rest of the line, which keeps parts and recurrent training reachable.

Key Features for GA Buyers

• 690-cabin pressurization without turbine acquisition cost. Roughly 5 psi differential cabin in a 9,000 lb piston airframe, sitting well below the 690’s price band on the used market.
• Genuine cabin-class capacity. Nine-seat interior (1-2 crew, 7-8 passengers), 600 lb baggage capacity, walk-in airstair door, and a flat floor courtesy of the high-wing carry-through.
• Long range with the auxiliary fuel option. Standard 256 USG gives roughly 1,251 NM; the optional 322 USG configuration extends that to about 1,655 NM at economy cruise – competitive with several contemporary turboprops on book numbers.
• High service ceiling for a piston twin. 27,500 ft service ceiling with comfortable long-range cruise in the low-to-mid 20s puts the 685 above weather more often than typical pressurized piston twins.
• Twin Commander Aircraft LLC type support. The same Service Center network that supports the 690, 695, and earlier Commander variants covers the 685; recurrent training and AD management are actively maintained.

Trade-offs

• GTSIO-520 powerplant economics. Geared, turbocharged, and fuel-injected, the GTSIO-520-F/K is among the most operationally demanding Continental piston engines: hot-start discipline, careful power management, expensive overhauls, and a shrinking pool of shops with current experience.
• Tiny production run, thin parts pool. 66 airframes built across six model years means airframe-specific parts often require salvage sourcing or fabrication; the 690 next door has parts commonality on many systems but not on the powerplants or engine mounts.
• Piston operating costs at turbine-airframe utility levels. The 685 carries a 690-class hangar footprint and pressurization maintenance domain on a piston-twin operating budget; buyers often find the total-cost-of-ownership envelope unflattering compared with a King Air 90.
• Frequently misattributed in listings and databases. The 685 is regularly described as an “Aero Commander 685” or conflated with the 680T/V/W turbine series or the 690 turbine variants; verify engine fitment, model year, and TC details on any candidate airframe.
• Aerodynamic refinements postdate the 685. Several of the 690’s later-production improvements (winglet kits, engine-nacelle refinements, larger windows on later -A/-B variants) are not retrofittable to the 685; the airframe represents the early-1970s state of the platform.

See Also

• Commander 690 – Direct turbine successor on the same airframe; the TPE331-powered 690 is what the 685 became when Rockwell committed to turbines for the family. Compare
• Cessna 421C Golden Eagle – Direct period peer and Wichita’s dominant pressurized piston cabin twin of the same era; twin TSIO-520-N turbocharged Continentals, a smaller and lower-MTOW cabin, and the deepest support network in the bracket. Compare
• Piper PA-31P Pressurized Navajo – Direct period peer with the closest powerplant economics: Lycoming TIGO-541-E1A geared turbocharged sixes whose maintenance domain and shrinking-support profile most closely mirror the 685’s GTSIO-520. Compare
• Beech 60 Duke – Pressurized piston cabin twin from the same era in a tighter cabin; TIO-541-E1A4 geared turbocharged Lycoming with a similar operational-demand profile to the 685’s GTSIO-520 – both engine families have shrinking support networks. Compare
• Aero Commander 680FP – Sister pressurized piston Commander on the earlier 680F airframe; IGSO-540 powerplant rather than GTSIO-520, and a smaller cabin. Compare
• Cessna 340A – Smaller pressurized piston cabin twin in the same general market segment; a step down in size, performance, and operating cost. Compare
• Aero Commander 680FL – Predecessor stretched-cabin Commander; unpressurized, IGSO-540-powered Grand Commander on the prior airframe lineage. Compare