ATR 42/72-600 Systems Guide — Chapter E: Automatic Flight Control System

2026-06-23

Chapter E. AUTOMATIC FLIGHT CONTROL SYSTEM (FCOM DSC 22)¶

1. AFCS CORE ARCHITECTURE (Page 55)¶

The Automatic Flight Control System (AFCS) coordinates the Flight Director (FD), Autopilot (AP), and Yaw Damper (YD) loops to provide precise guidance and stabilization control across the aircraft performance envelope.

  AFCS SYSTEM SCHEMATIC INTERFACE
  ┌────────────────────────────────────────────────────────┐
  │                      FGCP PANEL                        │
  │             (Mode Selections & Targets)                │
  └──────────────────────────┬─────────────────────────────┘
                             │
                             ▼
  ┌────────────────────────────────────────────────────────┐
  │              FLIGHT GUIDANCE COMPUTERS                 │
  │            [ FGC 1 ]           [ FGC 2 ]               │
  └─────────────────┬──────────────────┬───────────────────┘
                    │                  │
         ┌──────────┘                  └──────────┐
         ▼                                        ▼
  ┌──────────────┐                         ┌──────────────┐
  │ PRIMARY PFD  │                         │ SERVO MOTORS │
  │ (FMA Blocks) │                         │(Flight Paths)│
  └──────────────┘                         └──────────────┘

Core Processors: System computing is split across two redundant Flight Guidance Computers (FGC 1 and FGC 2) installed inside the main avionics bay framework. Only one FGC acts as the active system master at any given time, driving the autopilot servos directly.

2. FLIGHT MODE ANNUNCIATOR (FMA) SYSTEM REGIONS (Page 56)¶

The Flight Mode Annunciator (FMA) strip is integrated directly into the upper bezel region of the Primary Flight Display (PFD) to provide immediate status tracking of active and armed flight control modes.

  PFD FMA MODES LAYOUT
  ┌────────────────────────────────────────────────────────┐
  │  LATERAL MODES   │   AP/YD ENGAGEMENT   │ VERTICAL MODES │
  │                  │                      │                │
  │  [NAV ] [HDG]    │     AP 1   │  YD     │ [ALT ] [IAS]   │
  │  (Green) (White) │     (Green)  (Green) │ (Green) (White)│
  └──────────────────┴──────────────────────┴────────────────┘

Color Convention Rules:¶

Green Text: Identifies a system mode that is currently Active and guiding the aircraft.
White Text: Identifies an Armed capture mode. The system will activate this mode automatically once its capture coordinates are satisfied.
Amber Flashing Text: Indicates an automatic mode change, a sensor validation mismatch, or an emergency system disengagement.

2.1. FMA Lateral Control Modes Matrix (Page 57)¶

The system prioritizes lateral tracking based on five primary operational guidance pathways:

HDG SEL (Heading Select): Tracks the manual heading bug selected on the EFCP/ND control interface.
NAV (Navigation Mode): Tracks localized lateral guidance tracks from VOR stations, ILS Localizer arrays, or internal LNAV software lines.
APP (Approach Mode): Configures high-sensitivity tracking parameters for Category I / II ILS Localizer beams or precision GPS approach vectors.
BC (Back Course): Inverts tracking polarity parameters to permit instrument approaches utilizing localized back-course signal structures.
LNAV (Lateral Navigation): Couples flight tracking directly to active FMS navigation track legs.

2.2. FMA Vertical Control Modes Matrix (Page 58)¶

Vertical guidance profiles follow precise altitude, speed, and vertical speed constraints:

ALT HOLD (Altitude Hold): Tracks and maintains the specific pressure altitude reference active at the moment of button engagement.
ALT SEL (Altitude Select): Armed automatically when a new target altitude is dialed into the selector box. It manages the capture intercept trajectory safely.
VS (Vertical Speed): Tracks a constant target climb or descent velocity profile dialed into the pitch thumbwheel.
IAS (Indicated Airspeed Select): Modulates pitch parameters automatically to match and lock the current airspeed value.
VNV (Vertical Navigation): Couples vertical tracking profiles to FMS altitude constraints and glide path matrices.

3. FLIGHT GUIDANCE AND CONTROL PANEL (FGCP) LAYOUT (Page 59)¶

The FGCP is mounted centrally on the cockpit glaresheld to provide single-point mode management controls.

  FLIGHT GUIDANCE CONTROL PANEL (FGCP)
  ┌─────────────────────────────────────────────────────────────────────────┐
  │  COURSE 1   NAV SOURCE CAPT      HDG      NOSE DN     IAS      AP       │
  │   ( O )    [VILS1][VILS2][FMS1]  [   ]   ┌───────┐   [   ]   [   ]      │
  │                                  [NAV ]  │ Pitch │   [VS ]   [YD ]      │
  │                                  [APP ]  │ Wheel │   [VNV]              │
  │    [ FD ]                        [BC  ]  │       │   [ALT]   [CPL]      │
  │    [    ]    [ HDG PUSH SYNC ]   [STBY]  └───────┘   [   ]   [   ]      │
  └─────────────────────────────────────────────────────────────────────────┘

Core Interface Elements:¶

NAV SOURCE CAPT Selection Buttons: Set the sensor priority line (VILS1, VILS2, or FMS1) for the Captain's primary displays.
HDG Push Sync Dial: Controls manual heading targets. Pressing the dial syncs the target heading bug directly to the aircraft's current magnetic heading.
Pitch Thumbwheel: Rotates up or down to vary target pitch angles, vertical speed rates, or airspeed metrics depending on the active vertical mode.
AP / YD Engagement Switches: Dual magnetic-latch pushbuttons that couple FGC output to the primary flight control cable servos.

4. INDEX CONTROL PANEL (ICP) & COUPLING LOGIC (Page 60)¶

The system routing pathways require an explicit definition of sensor priority to prevent guidance loops from fighting conflicting telemetry parameters.

CPL Pushbutton (Coupling Selector): Links autopilot servo loops to either the left or right flight computer data streams:
CPL L (Left): Autopilot loops utilize the Captain's air data computer, FMS data, and flight director matrices.
CPL R (Right): Autopilot loops utilize the First Officer's air data computer, FMS data, and flight director matrices.
Automatic Disengagement Criteria: The autopilot servos will immediately trip offline, activate the Master Warning system, and trigger the cavalry charge acoustic alarm if any of the following conditions occur:
Active control surfaces encounter a physical jam.
Mismatched data parameters are detected between ADC 1 and ADC 2.
The aircraft's pitch or bank angle breaches safety margins ($>25^\circ$ bank or structural stall limits).

Chapter E. AUTOMATIC FLIGHT CONTROL SYSTEM (CONTINUED)¶

4.1. AFCS GO-AROUND (GA) MODE LOGIC (Page 61)¶

The Go-Around (GA) mode provides automated vertical and lateral guidance trajectories during a missed approach sequence.

Engagement Parameters: Triggered by pressing either of the dual GA buttons located on the forward side of the engine power levers.
FMA Phase Transitions:
Vertical Column: Switches immediately to GA (Green text), commanding a fixed symmetric pitch climb profile ($13.5^\circ$ initial pitch up target).
Lateral Column: Switches immediately to GA (Green text), locking the track profile to the heading active at the exact moment of button engagement.
Autopilot Behavior: Engaging GA mode automatically disengages the Autopilot (AP), while the Flight Director (FD) bars remain active to provide visual path steering commands. The Yaw Damper (YD) remains fully engaged to stabilize directional control.