Avionics Maker First To Certify Underspeed Protection That Guards Against Autopilot-Induced Stalls

Avidyne announced Thursday they have received FAA amended STC approval for their recently-certified DFC90 Digital Flight Control System which enables speed-based Flight Envelope Protection.

 
Avidyne DFC 90

"Avidyne's Flight Envelope Protection guards against autopilot and flight director-induced stalls and overspeeds, which lead to a significant number of GA accidents," said Patrick Herguth, Avidyne's Chief Operating Officer. "The DFC90 with Flight Envelope Protection provides significant safety enhancement, especially for pilots in high work-load IFR environments."     

"The certification of Flight Envelope Protection is a significant achievement for Avidyne, as well as a considerable step forward in general aviation autopilot performance and safety," said Avidyne President and CEO, Dan Schwinn. "Avidyne is committed to continuously enhancing safety for all of our customers, and Flight Envelope Protection, as well as the Straight and Level function and other capabilities of the DFC90, establish a new watermark in general aviation autopilot performance and safety."

Flight envelope protection is designed to significantly enhance safety by addressing many of the situations that lead to accidents. Accident data have pointed to many scenarios where Flight Envelope Protection could have made a positive difference.

One example scenario is when the pilot is descending at reduced power to the Final Approach Fix, where the autopilot captures the preseleced altitude. If the pilot were to get distracted on the radio or for other reasons and forgets to apply adequate power to maintain altitude, the DFC90's aural and visual "Underspeed" warning would make the pilot aware of his dangerously decaying airspeed and prompt him to take action, and the autopilot's Flight Envelope Protection would gently reduce the pitch of the airplane to maintain a 20% margin above stalling airspeed (1.2X Vs).

Another observed scenario shows how Flight Envelope Protection provides protection even in an engine out situation. In a Turbo airplane at high altitude, due to an oxygen system failure or oxygen exhaustion, the pilot has been incapacitated from hypoxia. The autopilot is engaged and holding altitude. The aircraft flies along until fuel starvation on the selected tank occurs causing the engine to stop. With existing autopilots, the autopilot will continue to try and hold the pre-selected altitude and fly the airplane into a stall. With Flight Envelope Protection, the autopilot would instead reduce the pitch of the airplane as airspeed declines due to lack of engine power, inducing a smooth descent. At a lower altitude with higher pressure and adequate ambient oxygen, the pilot could recover, assess the situation, switch tanks, perform a restart, and have a much more favorable outcome.

For Flight Envelope Protection, available lift and speed margin are calculated constantly whenever any autopilot or flight director modes are in operation. As the aircraft approaches stall, the autopilot gradually reduces bank (if in a turn) and pitch just enough to maintain a 20% airspeed margin over the stall speed, while visually and audibly annunciating the condition to the pilot. As a result, departure from controlled flight is prevented with the least impact on achieving mission-level objectives like navigation, climb or approach. Overspeed is handled similarly, with anticipation and minimal but effective inputs. In Flight Director modes, all these actions appear as guidance cues with corrections blended into the "V-bar" commands.

Display Showing An Underspeed Condition

The DFC90 is an attitude-based digital autopilot system that is designed as a slide-in replacement for the S-TEC55X autopilot in existing Entegra-equipped Cirrus SR20 and SR22 aircraft. The significant performance and safety benefits of the attitude-based DFC90 make it a very attractive upgrade for the more than 4,000 owners of Entegra-equipped Cirrus aircraft. 

The Release 8.0.2 software and Mod 55 PFD hardware upgrades enable the DFC90 autopilot to take advantage of the precision attitude information of Entegra's integrated Air Data and Attitude Heading Reference System (ADAHRS), without the need for costly wiring changes to the 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). Customers upgrading from the STEC 55X will notice several major performance and feature improvements including:

• Greatly improved stability due to the use of attitude data to control the autopilot inner control loops. This is particularly evident and important when tracking an ILS to minimums in windy conditions.
• Avidyne's speed-based Flight Envelope Protection virtually eliminates autopilot-induced stalls (underspeed) and overspeeds, which lead to a significant number of GA accidents. With Flight Envelope Protection, the autopilot avoids exceeding the flight envelope while providing visual and aural warnings to the pilot.
• The new Indicated Airspeed Hold (IAS) vertical mode includes a dedicated Airspeed knob and a new airspeed bug on the PFD, and provides a more elegant way to make Flight Level changes.
• The"Straight & Level" button overrides all autopilot modes and levels the aircraft in both pitch and roll from a wide range of capture attitudes for an added measure of safety.
• The Flight Director capability of the DFC90 is vastly improved and greatly improves the ability to hand-fly approaches.

There are many other improvements, such as a dedicated Vertical Speed knob, pitch hold mode, wide autopilot engagement, additional annunciations in PFD 8.0.2, a dedicated GPSS button, automatic Back Course Approach selection, multiple color annunciations to indicate armed and active states, intercept mode annunciations, and Avidyne's hallmark ease of use.

The retail price of the DFC90 Digital Flight Computer is $9,995. The cost of Release 8.0.2/Mod 55 is $3,895 for PFDs that are at Release 7. The cost of Release 8.0.2/Mod 55 is $5,395 for PFDs that at are currently at Release 6 or older.

DFC90s are now shipping, and PFDs with Release 8.0.2 and MOD 55 enhancements are available through Avidyne's Platinum Exchange program.

FMI: www.avidyne.com