Engage the autopilot roll and pitch modes. Manually override the control yoke in all directions. The slip clutches in the servos must slip smoothly without mechanical jamming.
This paper serves as a technical overview and procedural guide for the installation of the S-TEC System Fifty Five X (55X) autopilot system. As one of the most prevalent General Aviation autopilot systems, the 55X requires precise integration with an aircraft’s existing pitot-static, electrical, and flight control systems. This document outlines the regulatory framework, physical installation considerations, electrical interfacing, and the mandatory post-installation testing protocols required for airworthiness certification.
The panel-mounted control unit contains the inner-loop logic, microprocessor, and user interface. It must be installed in the primary instrument panel within easy reach of both pilots. Turn Coordinator (Model 6405)
The internal slip clutches of the servos must be tested using a calibrated torque wrench. S-tec 55x Installation Manual
The installation requires a main wire harness kit. It is critical to use the correct gauge wire, shielded cables where necessary (especially for audio and sensitive analog signals), and properly crimped pins to ensure a reliable connection.
The Mode Controller (S-TEC P/N 0124X or similar) is the pilot interface. Installation involves:
Ensuring the aircraft intercepts and holds headings without hunting or oscillating. Engage the autopilot roll and pitch modes
The System 55X integrates with a wide variety of GPS, HSI, and EFIS systems via digital ARINC 429 buses or traditional analog steering lines (Left/Right, Up/Down deviations).
The (e.g., Garmin GNS430, GTN650, or an EFIS system) If you are troubleshooting an existing installation error
: Must be installed by an FAA-certified avionics technician or equivalent authority. This paper serves as a technical overview and
Because the pressure transducer was spliced into the static lines, a standard pitot-static system leak test per FAA 14 CFR Part 91.411 must be completed successfully. Ground Diagnostic Sequence
Turn on the avionics master. The S-TEC 55X should run through a brief internal diagnostic self-test, illuminating all display segments.
The System 55X is a rate-based autopilot. It derives its roll and yaw stabilization data from a modified electric Turn Coordinator. This gyro must be mounted perfectly level relative to the aircraft’s lateral and longitudinal axes. Servos (Pitch, Roll, and Trim)