SAN DIEGO, Calif., 4 Feb. 2010 Express Logic's ThreadX real-time operating system (RTOS) is driving Avidyne Corp.'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 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. The RTOS 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," says Mark Krebs, Avidyne's vice president of 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."

Avidyne has completed this development and testing, and expects FAA DO-178B 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," says 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."

ThreadX has only about 20,000 liens of code to certify, Lamie continues, which makes it much less labor intensive to certify. Lamie adds that Express Logic is developing a DO-178B certification kit that will enable users of the RTOS to more quickly certify the systems.

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

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.