High-performance, two-axis (roll & pitch) autopilot in an avionics stack-mounted case, containing the mode selector/programmer, annunciator, roll & pitch computers, and servo amplifiers.The S-Tec System 55X incorporates the GPS Roll Steering and tracking with glide slope capture and track, VOR/localizer/back course intercept and tracking, and vertical speed commands. The System 55X Computer/Programmer has an LCD digital display and is designed for mounting in the standard avionics stack. Options include heading pre-select, auto-trim, altitude pre-select, remote annunciator, etc.

Display Screen

HDG (heading) mode & heading preselect and hold*

When HDG & NAV are activated simultaneously, enables dual mode Intercept. Autopilot operates in heading mode to automatically intercept and track selected course or localizer; at which point HDG extinguishes.

Control wheel steering (CWS)

Allows you to hand-fly the aircraft and then let the autopilot takeover to hold the existing turn rate and vertical speed.

NAV mode (coupled navigation)

Automatically intercepts and tracks enroute NAV signals (VOR/GPS), or LOC (REV for backcourse). 3-level gain selection for NAV mode is automatic. When APR is lit (simultaneous with NAV), indicates high gain localizer mode for high sensitivity coupled approach. Flashing NAV or REV annunciates course deviation by a needle deflection of 50% or more. Selecting APR increases gain sensitivity for VOR or GPS approaches.

GPSS (GPS Steering)

Integrates A/P with GPS Navigator function, which outputs roll steering commands. GPSS does not follow a CDI needle movement; it acts on direct roll steering commands from the Navigator for extremely accurate, hands-off GPS navigation. See separate GPSS data sheet for details.

TRIM and up/down arrows.

Annunciate motion of auto trim or manual electric trim, if equipped; if not equipped, annunciates out-of-pitch-trim condition. 6 Pitch Mode. Includes VS, indicating vertical speed control has been selected; ALT indicating altitude hold is engaged, capturing existing altitude when activated; and GS, indicating glide slope coupling is armed and/or active. In altitude hold mode, altitude can be adjusted (trimmed) in 20’ increments using VS knob.


Mode selector buttons

HDG (heading hold and heading pre-select*), NAV (tracking VOR route or select twice for GPSS), APR (higher gain for LOC/VOR and GPS approaches), REV (LOC backcourse), ALT (altitude hold) and VS (vertical speed command).

VS knob

Dials digital vertical speed in 100’ increments. *Operational if heading system (e.g., DG with heading bug) is installed and active.

System Fifty Five X: features and functions

  • Case contained, radio stack mount
  • GPSS (GPS Roll Steering)
  • Heading preselect & hold*
  • Altitude hold with optional altitude trim
  • Course intercept capability
  • NAV mode
  • Dual mode-HDG/NAV & HDG/APR
  • VOR/LOC/GS/REV/GPS coupling with 3 gain levels
  • Selectable coupling gains
  • VOR/LOC/GS/REV/GPS course deviation and NAV flag warning
  • Digital vertical speed command
  • Pitch trim annunciation
  • Control wheel steering