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and grew in size and presentation detail. Autopilots were upgraded from rate-based analog units to attitude-based digital units. Then, in the mid-2000s, WAAS-capable GPS units were made available to the masses, and digital glide paths into runways big and small, moved from fantasy to reality. Nevertheless, while autothrottle technology improved dramatically across this same timeline, it only did so in large turbojet aircraft, leaving cabin class pilots clutching and tweaking their throttles in the same way they’d been doing for the previous 50 years or more.
Dreaming in Digital
Through the 2010s, digital avionics and autopilots got smaller, better, faster, and more feature-rich. Their use soon became the norm in production aircraft and was sweeping through the retrofit market. Retrofit companies began offering the latest technologies in comprehensive upgrade packages, which included improved engines, techy cabin enhancements, and complete flight deck makeovers. None of those packages had a turboprop au- tothrottle system, but it was being developed behind the scenes. As digital hardware became smaller and smaller, the feasibility of squeezing autothrottle components into the crowded spaces of cabin-class cockpits began to seem realistic. Meanwhile, software advances made the complex task of automating turboprop power manipulation pos- sible. The time had finally arrived for turboprop pilots to join their jet counterparts and enjoy the enhancements autothrottles could bring to flight safety and efficiency.
Like so much in aviation, change can be slow, even during times of rapidly advancing technology. This is a good thing too. New technologies need vetting, testing, and detailed scrutiny. When applied to certified aircraft, they must be proven to be safe and reliable. That process takes time measured in years, not days, and mountains of capital investment. Thus, while turboprop autothrottles were spoken of often throughout the 2010s, it was in the late 20-teens that news of certifications began to break. Initially, those certifications were retrofit systems only. However, several companies are now offering new produc- tion turboprops with autothrottle systems, too.
Pseudo FADEC
Another technology that has been around for decades now is Full Authority Digital Engine Control (FADEC). It allows pilots to move power levers as the situation demands without fear of exceeding engine limitations (torques, temperatures, pressures, etc.). The computer “reads” the pilot’s throttle “command” and provides the closest engine output to that command without exceeding any operational limits. Like autothrottle, though, FADEC has primarily been limited to turbojet engines. One of the principal challenges of developing and certifying a turboprop autothrottle system is getting that system to work without the input of FADEC data. The Pratt & Whitney PT6A turboprop engine is far and away the most common in cabin-class turboprop aircraft today. What
it is not, however, is digital. It operates via decades-old analog/hydromechanical technology. Highly reliable and versatile as it may be, strapping an autothrottle to a PT6A was a complex matter of tapping into the FADEC to utilize its data and software capabilities since no such FADEC existed.
The not-so-secret sauce is provided by linking elec- tromechanical components that control power output to hardware and software that constantly monitor engine parameters and trends. Along with this comes the equally safety-enhancing abilities to select and hold a desired indi- cated airspeed (IAS) and envelope and stability protection features that will kick in if a distracted pilot allows IAS to reach low or high-speed limits that could potentially cause a stall or structural damage. Additional safety features allow for speed protection in turbulent air or the auto- matic setting of maximum range or maximum endurance power. Of course, all this must also communicate with the autopilot systems to couple autothrottle adjustments to achieve the IAS, Altitude, Vertical Speed, and Navigation commands input by the pilot. In multi-engine aircraft (such as King Air variants), the autothrottle system must be capable of helping to manage an engine failure situation by adjusting power on the operating engine to achieve safe performance parameters and to assist in avoiding (or recovering from) a Vmca situation, for instance.
Retrofittable
In 2018, Innovative Solutions & Support (IS&S) achieved certification and began delivery of an autothrottle system for the Pilatus PC-12 (image page 22). Dubbed “Thrust- Sense,” the system is retrofittable in two ways, depending on the cost the buyer can justify and other enhancements they might desire. Simply adding autothrottle capabilities requires the addition of IS&S’s Integrated Standby Unit (ISU), which can replace any existing standby instru- ments. The ISU provides the software and control panel necessary to control the PT6A engine. Or, the owner could bundle the addition of autothrottle and ISU with a complete panel upgrade via IS&S’s NextGen 3015 sys- tem. The 3015 includes dual PFDs, a large central MFD/ Engine Display, WAAS, ADS-B In/Out, VNAV, RNP & LPV, electronic charts, TAWS, SynVis, radar, satellite weather capabilities, etc. Similar upgrade paths to ThrustSense are available from IS&S for the King Air 200 and 300 series. ThrustSense retrofit options for other cabin-class turboprops are in development, as well.
Factory Installed
First to market with an autothrottle system for a cabin- class turboprop was Daher, which introduced autothrottle capabilities to its TBM lineup with the TBM-940 model in 2019. All autothrottle control and programming are handled via the Garmin 3000 avionics suite and its req- uisite assortment of sensors and software. As of this writing, the TBM-960 is the Daher flagship, still sporting the G3000 and autothrottle. Piper followed soon after
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