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Express Logic’s THREADX® RTOS Selected for Avidyne Digital Flight Control System

San Diego, CA (November 23, 2009)

Express Logic, Inc., the leader in royalty-free real-time operating systems (RTOS), today announced that its popular THREADX® RTOS drives Avidyne Corporation’s new DFC90 attitude-based Digital Flight Control System. The DFC90 is an integrated flight computer and control panel designed as a slide-in replacement for existing rate-based STEC 55X flight computers. Avidyne’s DFC90 specifically targets Cirrus SR20 and SR22 aircraft with Avidyne’s Entegra Flight Deck Systems.

THREADX is Express Logic’s small, fast, reliable RTOS for deeply embedded real-time applications, such as Avidyne’s new aircraft flight control system. In a flight control system, aircraft flight is controlled by servos that deflect aelerons and elevator control surfaces to induce turns and/or pitch changes for climb or descent. The DFC90 flight control system receives input regarding the aircraft’s attitude, heading, and altitude, as well as input from the pilot and navigation system that specify the desired attitude, heading, altitude, and rate of climb/descent. The DFC90 calculates the precise commands that drive the servos in real time, so that the desired flight path is achieved.

As the operating system powering Avidyne’s flight control system, THREADX controls all functions in the DFC90. THREADX delivers low overhead and fast real-time response, critical requirements for systems such as Avidyne’s DFC90.

“Developing flight critical systems is hard enough without worrying about the RTOS,” noted Mark Krebs, Avidyne’s VP Engineering for Guidance and Controls. “Avidyne is pleased to introduce a new level of performance and safety to General Aviation lightplanes with our DFC90 and DFC100 Cirrus autopilot. THREADX software was easy to use, rock solid and high performance. We won’t be looking anywhere else for our next RTOS.”


The FAA requires that all operational software in an aircraft that flies in US airspace be developed and certified in conformance with DO-178B, a safety-critical software standard used widely in other industries as well. DO-178B requires detailed documentation and testing of the entire software system, including the RTOS. Avidyne has completed this development and testing, and expects FAA certification for the DFC90 in mid-2010. Avidyne reports that THREADX represented only a small percentage of the overall software system, adding minimal code requiring certification.

“Avidyne’s new DFC90 has many new, advanced, state-of-the-art safety features, yet it required nothing our THREADX RTOS couldn’t provide,” said William E. Lamie, President of Express Logic. “Avionics systems—an application requiring rigorous government certification—can depend on THREADX to handle a system’s technical requirements, and be easily certified to DO-178B.”

DFC90 Autopilot

Avidyne’s DFC90 Attitude-Based Digital Autopilot enhances flight precision and improves safety for Entegra-equipped Cirrus SR20 and SR22 aircraft.

The DFC90 adds the precision of an attitude-based flight control system and Avidyne’s innovative, safety-enhancing Envelope Protection capability.

The DFC90 has all the standard vertical and lateral modes of operation of a turbine-class autopilot system, including Flight Director (FD), Altitude Hold (ALT), Airspeed Hold (IAS), Vertical Speed Hold (VS), Heading (HDG), and Navigation (NAV, APPR, LOC/GS, GPSS). The DFC90 also includes Avidyne’s “Straight & Level” button, which overrides all autopilot modes and levels the aircraft in both pitch and roll for an added measure of safety. For envelope protection, available lift and speed margin are monitored constantly regardless of the mode of operation. As the aircraft approaches stall, the autopilot gradually reduces maximum bank and vertical speed just enough to keep the wing flying, while annunciating the condition to the pilot. As a result, departure from controlled flight is prevented with the least obtrusive impact on achieving mission-level objectives like navigation, climb or approach. Overspeed is handled similarly, with anticipation and minimal but effective inputs.

“The DFC90 raises the bar on light aircraft flight control,” noted John Carbone, Express Logic vice-president of marketing, and an instrument-rated pilot. “It gives me an extra level of confidence to know that Cirrus flights will be controlled by a flight system powered by THREADX. With over 650 million deployments, THREADX has earned its stellar reputation as a robust, rock-solid RTOS.”

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