ItРІР‚в„ўs 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.Р”Р„ttitude-based systems do all of that more precisely than a rate-based system. ThatРІР‚в„ўs because what weРІР‚в„ўre 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, itРІР‚в„ўs easy to have unrealistic expectations on what a modern system can do and how well it might perform. HereРІР‚в„ўs a look at the current retrofit autopilot market thatРІР‚в„ўs trending toward digital interfaces, increased reliability and higher costs. ItРІР‚в„ўs a drop-in, AHRS-based solution for replacing and increasing the performance of existing S-Tec systems. But S-Tec isnРІР‚в„ўt the only game in town.Р”В¬entury and Bendix King still build autopilots, too. ThatРІР‚в„ўs roughly the cost of an average engine replacement-or an average Skyhawk.Р”Р‡or 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.

Stec 50 autopilot tracking problems