CD Aviation Services Acquires STC for Twin Commander Engine Upgrade

CD Aviation Services (CDAS), a specialized turbine engine maintenance provider, has officially announced the acquisition of Supplemental Type Certificate (STC) SA1024SO. According to the company’s press release, this certification authorizes the installation of Honeywell TPE331-5-252K engines on the Twin Commander 690, 690A, and 690B Commercial-Aircraft series. The STC, previously associated with Aero Air, LLC, provides a Federal Aviation Administration (FAA)-approved pathway for operators to upgrade their legacy powerplants.

For the legacy aviation community, this acquisition represents a critical development in maintaining the airworthiness of aging fleets. The core of the upgrade involves transitioning the aircraft’s fuel control system from the older Bendix configuration to the more widely supported Woodward system. By bringing this STC in-house, CDAS aims to directly support Twin Commander operators facing growing industry concerns over parts availability and maintenance bottlenecks.

As out-of-production aircraft continue to age, the availability of approved modifications is vital for their continued operation. The official announcement highlights that this STC not only modernizes the engine configuration but also aligns the aircraft with current industry maintenance standards, ensuring these vintage twin-turboprops remain viable for years to come.

Technical Details of the Engine Upgrade

Transitioning from Bendix to Woodward Fuel Systems

The primary technical shift facilitated by STC SA1024SO is the conversion from the Honeywell TPE331-5-251K engine to the TPE331-5-252K engine. According to the provided research data, the most significant change in this upgrade is the replacement of the legacy Bendix Fuel Control Unit (FCU) with a Woodward FCU. The conversion is performed in strict accordance with Honeywell Service Bulletin SB 72-0216, which outlines the necessary steps for transitioning between the two fuel control systems.

Understanding the differences between these two systems is essential to grasping the value of the STC. The legacy Bendix system, found on early TPE331-5 engines, was largely air-based. Historical maintenance data indicates that these units were prone to operational issues, such as moisture freezing within the system. Today, Bendix-equipped engines represent a minority in the active fleet, and operators face severe challenges due to decreasing parts availability and limited overhaul support.

Conversely, the Woodward FCU is a predominantly hydraulic system that has become the industry standard for these engines. While the Woodward system has faced its own historical airworthiness directives, such as AD 2006-15-08, which required a switch from steel to plastic fuel splines to prevent runaway engines, it is vastly more serviceable within the modern aviation maintenance network. Furthermore, upgrading to the Woodward system is a prerequisite for further engine enhancements, such as the -10 upgrade.

Impact on the Twin Commander Fleet

Extending the Lifespan of Legacy Aircraft

The Twin Commander 690 series consists of twin-turboprop executive business aircraft built primarily between 1972 and 1979. Known for their high-wing design, impressive climb rates, and cruise speeds of up to 250+ knots, these aircraft remain popular in the used market. Because the airframes have been out of production for decades, maintaining and upgrading their powerplants is critical for their continued airworthiness.

The acquisition of this STC by CDAS offers tangible benefits to operators of these vintage aircraft. By providing a legal and practical method to replace obsolete Bendix systems, the STC effectively extends the operational lifecycle of the Twin Commander 690 series. Operators will no longer have to hunt for scarce Bendix components, as the -252K configuration offers much broader parts availability across the global supply chain.

Additionally, the Woodward system is widely understood across the global maintenance network. This familiarity leads to expanded overhaul capabilities and potentially lower maintenance downtimes for operators, ensuring that these legacy aircraft can be serviced efficiently by authorized repair stations worldwide.

“This STC provides operators with a clear and practical path forward when evaluating engine upgrades or addressing long-term support concerns. Our focus is on delivering solutions that improve aircraft reliability, maintainability, and overall lifecycle support.”

About CD Aviation Services

Headquartered in Joplin, Missouri, CD Aviation Services has specialized in small turbine engine maintenance for over 20 years. According to company statements, they operate as a Honeywell Authorized Part 145 repair station, focusing specifically on Honeywell TPE331 and TFE731 engines, as well as GTCP36 series Auxiliary Power Units (APUs).

The strategic acquisition of STC SA1024SO expands the company’s in-house capabilities, allowing them to directly support Twin Commander operators rather than relying on third-party certificate holders. This move solidifies their position as a dedicated support hub for legacy Honeywell turbine engines.

AirPro News analysis

We view the acquisition of STC SA1024SO by CD Aviation Services as indicative of a broader trend within the aviation maintenance, repair, and overhaul (MRO) sector. As original equipment manufacturers (OEMs) naturally shift their focus toward newer platforms, specialized MROs are stepping in to acquire the intellectual property and certifications necessary to keep legacy fleets airborne. By taking ownership of this STC, CDAS is not merely offering a repair service; they are actively solving a critical Supply-Chain bottleneck regarding the obsolete Bendix FCU. This proactive approach is essential for the survival of out-of-production airframes like the Twin Commander 690, ensuring that operators have a predictable, FAA-approved path for modernization and continued Compliance.

Frequently Asked Questions (FAQ)

What aircraft does STC SA1024SO apply to?
According to the FAA-approved certificate details, the STC applies specifically to the Twin Commander 690, 690A, and 690B series aircraft.

What is the main difference between the Bendix and Woodward FCU?
The legacy Bendix Fuel Control Unit is an older, air-based system that suffers from parts scarcity and historical reliability issues (such as moisture freezing). The Woodward FCU is a newer, hydraulic-based system that serves as the current industry standard, offering better parts availability and broader maintenance support.

Why is this STC important for Twin Commander operators?
It provides a legal, FAA-approved method to upgrade from the TPE331-5-251K engine to the -252K configuration, allowing operators to abandon the obsolete Bendix fuel system in favor of the supportable Woodward system, thereby extending the aircraft’s operational lifespan.

Sources

• CD Aviation Services