You’ll still need a backup attitude gyro, but it doesn’t need to have the outputs for driving the autopilot. They’re more precise, reliable and promise a longer life. A rate-based autopilot works by reference from a rate gyro inside an electric turn coordinator, arguably a less stable reference, especially in turbulence as the turn coordinator bounces.Īs we reported in the instrument upkeep article in the January 2013 issue of Aviation Consumer, PFD systems equipped with non-spinning, electronic gyros have become the preferred sources for driving autopilots. An attitude-based autopilot computer receives roll and pitch signals from a compatible attitude gyro (or digital AHRS, in a PFD-equipped aircraft).
It’s all about the precision and stability of the reference source that feeds the autopilot computer. In addition, we expect full-featured systems to precisely fly all segments of an instrument approach, including course reversals and holding patterns, following the lead of integrated GPS navigators and FMS systems.Īttitude-based systems do all of that more precisely than a rate-based system. That’s because what we’re really asking the system to do is maintain aircraft stability, particularly when turbulence and out-of-trim conditions depart the airframe from the intended roll-and-pitch axis. Rather than an automatic pilot, the better description is flight control system. Since pilots buy autopilots to fly the aircraft more smoothly and with more accuracy than a human, it’s easy to have unrealistic expectations on what a modern system can do and how well it might perform. Here’s a look at the current retrofit autopilot market that’s trending toward digital interfaces, increased reliability and higher costs. It’s a drop-in, AHRS-based solution for replacing and increasing the performance of existing S-Tec systems. But S-Tec isn’t the only game in town.Ĭentury and Bendix King still build autopilots, too.
That’s roughly the cost of an average engine replacement-or an average Skyhawk.įor years, S-Tec (now Cobham Avionics) has dominated the autopilot retrofit market with thousands of STC approvals, from Cessna 150s to Beech 1900s. Higher-end models with add-on options can easily snowball a project to $40,000. Even entry-level wing-leveling systems start at $10,000, not including installation.
Proposals for new autopilot upgrades can be shocking.
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