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ATR 42/72-600 Systems Guide — Chapter F: Communications

2026-06-23

Chapter F. COMMUNICATIONS (FCOM DSC 23, 34)

1. SYSTEM SCHEMATIC OVERVIEW (Page 62)

The Communications system (ATA 23) coordinates all short-range and long-range radio transceivers, data link paths, cabin address loops, and maintenance interphones.

  AUDIO MANAGEMENT INTERFACE TOPOLOGY
  ┌────────────────────────────────────────────────────────┐
  │                 COCKPIT HEADSETS / MASKS               │
  └───────────────────────────┬────────────────────────────┘
                              │
                              ▼
  ┌────────────────────────────────────────────────────────┐
  │               AUDIO CONTROL PANELS (ACP)               │
  │        (Station Level Transmission & Volume Selects)   │
  └───────────────────────────┬────────────────────────────┘
                              │
                              ▼
  ┌────────────────────────────────────────────────────────┐
  │              AUDIO MANAGEMENT UNIT (AMU)               │
  │        (Central Allocation Electronic Rack Matrix)     │
  └─────┬─────────────┬─────────────┬─────────────┬────────┘
        │             │             │             │
        ▼             ▼             ▼             ▼
    [VHF 1]       [VHF 2]       [VHF 3]        [ PA ]
  (ATC Comm)   (Data/Company) (Aux/Guard)   (Cabin Seats)
  • Audio Management Unit (AMU): A centralized digital processor rack that manages audio channel priority lines, side-tone validation loops, and line isolation protocols across all flight deck terminals.

2. PTT AND NOSE WHEEL STEERING GRIP MECHANICS (Page 63)

Radio transmissions and internal communications are managed via split-action controls mounted directly to the flight crew control yokes.

  CONTROL YOKE LEFT GRIP SWITCH DETAIL
  ┌────────────────────────────────────────────────────────┐
  │      [ PTT ] ──► Up: INT (Hot Intercom Loop)           │
  │                  Down: RAD (VHF Transmission)          │
  │                                                        │
  │      [ NWS ] ──► Push-and-Hold: Rudder Pedal Steering  │
  │                  Disconnect / Ground Override          │
  └────────────────────────────────────────────────────────┘

2.1. Push-To-Talk (PTT) Toggle Operation:

  • INT Position (Toggle Pressed Up): Connects the microphone directly to the internal flight deck and cabin interphone loop. This creates an open channel without broadcasting over external radio frequencies.
  • RAD Position (Toggle Pulled Down): Activates the transmitter lines of the specific VHF or HF radio channel selected on the active Audio Control Panel.

2.2. Nose Wheel Steering (NWS) Switch:

  • Placed on the yoke grip to permit quick disconnect indexing. Pressing the switch toggles priority control pathways between the hydraulic steering actuators and the primary rudder pedals during runway tracking transitions.

3. AUDIO CONTROL PANEL (ACP) LAYOUT (Page 64)

Three identical ACPs are installed on the center pedestal (Captain, First Officer, and an optional third observer station on the rear console).

  AUDIO CONTROL PANEL (ACP) LAYOUT
  ┌────────────────────────────────────────────────────────┐
  │  VHF 1    VHF 2    VHF 3     HF 1      INT      PA     │
  │  [ X ]    [   ]    [   ]     [   ]    [   ]    [   ]   │
  │                                                        │
  │  ( O )    ( O )    ( O )     ( O )    ( O )    ( O )   │
  │                                                        │
  │   RAD               VOICE              AUDIO SEL       │
  │  [   ]              [   ]               [NORM]         │
  │   INT               IDENT               [ALT ]         │
  └────────────────────────────────────────────────────────┘

3.1. ACP Control and Selection Matrix (Page 65)

Component Type Control Label Selection / Operational System Logic
Transmission Keys VHF 1 / 2 / 3, HF 1, INT, PA Pushbutton switches. Depressing a key selects that specific system for transmission. A green indicator strip illuminates above the active channel. Only one transmission channel can be active at a time.
Reception Knobs Volume Dials Push-to-release rotary potentiometers. Pressing the knob pops it outward to activate audio monitoring for that channel. Rotating the knob adjusts individual volume levels. Multiple channels can be monitored simultaneously.
RAD / INT Toggle Mode Switch A manual fallback toggle switch. Replicates the functionality of the yoke PTT switch for continuous stationary communication profiles.
VOICE / IDENT Filter Switch VOICE: Filters out continuous Morse code station identifiers to improve voice clarity during navigation checks.

IDENT: Bypasses filters to allow verification of Morse code station signals. | | AUDIO SEL Switch | Emergency Guard | NORM: Normal operating logic loops through the primary AMU modules.

ALT (Alternate): Hardwires the station terminal directly to a dedicated backup transceiver if an AMU computer module fails (Capt hardwires to VHF 1, F/O to VHF 2). |

4. VHF RADIO TUNING AND FREQUENCY CONTROL (Page 66)

Primary radio frequency entry and channel scheduling are driven digitally via the Multi-Function Computer Display Units (MCDU) on the central console.

  • MCDU COM Page Access: Pressing the COM function key calls up the active/standby frequency matrix for VHF 1, VHF 2, and VHF 3.
  • Frequency Transfer: Entering digits into the scratchpad and pressing the respective side key updates the standby memory buffer. Pressing the central transfer arrow toggle (◄►) swaps the standby frequency into the active broadcast stage.

5. CALLS OVERHEAD PANEL LAYOUT (Page 67)

Located on the forward overhead console panel. Controls alerts between the flight deck, passenger cabin, and ground maintenance bays.

  CALLS INTEGRATION CONTROL PANEL
  ┌────────────────────────────────────────────────────────┐
  │                         CALLS                          │
  │                                                        │
  │       ATT           MECH          CABIN          FWD   │
  │      [   ]         [    ]         ALERT         ALERT  │
  │                    [PROP]         (Red)         (Red)  │
  └────────────────────────────────────────────────────────┘

5.1. Signaling Logic States:

  • ATT Pushbutton: Signals the forward cabin attendant station. This illuminates an advisory panel in the cabin and plays a high-low tone chime.
  • MECH Pushbutton: Commands an external ground call horn inside the nose landing gear bay to sound. This alerts ground crews during pre-flight walkarounds.
  • PROP Indication (Amber): Flashes if a ground configuration fault is detected while the engine is running in Hotel Mode (propeller brake engaged).

6. ATC TRANSPONDER & TCAS CONTROL INTEGRATION (Page 68)

The transponder panel handles squawk tracking and controls the Traffic Alert and Collision Avoidance System (TCAS).

  ATC / TCAS CENTRAL CONTROL INTERFACE
  ┌────────────────────────────────────────────────────────┐
  │   [ 4 3 2 1 ] ◄── Squawk Code Register Display         │
  │                                                        │
  │    MODE SEL:      XPDR SEL:       TRAFFIC MODE:        │
  │    ( STBY )        (  1  )         (   ABOVE   )       │
  │    (ALT ON)        (  2  )         (   NORM    )       │
  │    (TA/RA )                        (   BELOW   )       │
  └────────────────────────────────────────────────────────┘

6.1. Mode Selection Rules:

  • STBY (Standby): The transponder isolates its RF output lines; no responses are broadcast.
  • ALT ON (Altitude Reporting): Transmits active Mode S squawk codes and pressure altitude data to ground radar arrays. TCAS processing remains disabled.
  • TA/RA (Traffic Advisory / Resolution Advisory): Full utility activation. Evaluates nearby traffic parameters. Generates visual target icons on the Navigation Display (ND) and outputs vertical coordination maneuvers via synthesized voice alerts if an un-cleared flight path conflict occurs.

7. COCKPIT VOICE RECORDER (CVR) PANEL LAYOUT (Page 69)

Located on the overhead panel space.

  CVR SYSTEM CONTROL PANEL
  ┌────────────────────────────────────────────────────────┐
  │                          CVR                           │
  │                                                        │
  │     STATUS        TEST         ERASE        HDST JACK  │
  │     (Green)      [ PUSH]      [ PUSH]         ( O )    │
  │                                                        │
  └────────────────────────────────────────────────────────┘
  • TEST Pushbutton: Pressing and holding this button tests the system's internal channels. A green status light confirms normal operation.
  • ERASE Pushbutton: Wipes recorded audio data from the solid-state memory tracks.
  • Safety Interlock Logic: The internal memory erase loop is disabled unless the aircraft is on the ground with the parking brake fully engaged (ON).

8. EMERGENCY LOCATOR TRANSMITTER (ELT) OPERATION (Page 70)

The Emergency Locator Transmitter (ELT) architecture provides automated emergency broadcasting if the airframe encounters extreme deceleration.

  • Impact Activation: Internal G-switches trigger an immediate broadcast if structural impact boundaries are exceeded. It transmits emergency signals across international search-and-rescue frequencies ($121.5\text{ MHz}$ and $406\text{ MHz}$).
  • Oxygen Mask Microphone Interlocks: The flight crew oxygen mask features an integrated microphone. Opening the oxygen mask container doors activates an internal microswitch. This action isolates the standard headset boom mic lines and routes the mask microphone directly into the active ACP channel to ensure clear communication during emergency descents.

Chapter F. COMMUNICATIONS (CONTINUED)

11. HEADSET, BOOM SET, AND HAND MICROPHONE INTERFACES (Page 71)

The flight deck provides dedicated hardware terminals at each crew station to interface headsets, oxygen mask microphones, and hand microphones with the Audio Management Unit (AMU).

11.1. Station Jack Allocation

  • Captain / First Officer Lateral Panels: Contain dedicated jack ports for:
  • High-fidelity boom-microphone headsets.

  • Handheld microphones (Handmikes).

  • Observer / Third Occupant Panel: Located on the aft center pedestal structure, providing independent jack connections linked to Audio Control Panel 3 (ACP 3).

  • Service Interphone System Ground Jacks: External maintainer plug points are physically distributed across the airframe to allow point-to-point communications during maintenance or ground handling ops:
  • Nose landing gear bay (adjacent to the ground calls panel).
  • Main avionics bay electronics rack.
  • Aft cabin service area.
  • Refueling control panel enclosure.

12. PUBLIC ADDRESS (PA) AND CABIN CA ALERT LOGIC (Page 72)

The Public Address (PA) system allows flight crews to broadcast announcements directly to the passenger cabin loudspeakers and handles high-priority chime generation.

12.1. System Priority Override Matrix

To ensure critical flight crew announcements are never blocked, the AMU applies a hardwired priority hierarchy across the PA network. Higher priority channels automatically mute lower priority transmissions:

  PA SOURCE PRIORITY MATRIX
  ┌────────────────────────────────────────────────────────┐
  │ Priority 1: CAPTAIN PA INTERACTION     (Highest)       │
  └───────────────────────┬────────────────────────────────┘
                          ▼
  ┌────────────────────────────────────────────────────────┐
  │ Priority 2: FIRST OFFICER PA INTERACTION               │
  └───────────────────────┬────────────────────────────────┘
                          ▼
  ┌────────────────────────────────────────────────────────┐
  │ Priority 3: FORWARD CABIN ATTENDANT HANDSET            │
  └───────────────────────┬────────────────────────────────┘
                          ▼
  ┌────────────────────────────────────────────────────────┐
  │ Priority 4: AFT CABIN ATTENDANT HANDSET                │
  └───────────────────────┬────────────────────────────────┘
                          ▼
  ┌────────────────────────────────────────────────────────┐
  │ Priority 5: PRE-RECORDED ANNOUNCEMENTS / MUSIC (Lowest)│
  └────────────────────────────────────────────────────────┘

12.2. Cabin Call Sound Profile Definitions

  • Flight Deck to Cabin Attendant: Plays a discrete high-low chime sequence through the cabin speakers and illuminates a green/cyan call light on the cabin area indicator panels.
  • Cabin Attendant Emergency Call to Flight Deck: Triggers a unique acoustic red alert signal sequence. This illuminates the CABIN ALERT or FWD ALERT red warning lights on the cockpit overhead Calls panel, bypassing normal volume attenuation limits.

13. ADDITIONAL COMMUNICATIONS SYSTEMS SUMMARY (Page 73)

Integrated communications telemetry links maintain peripheral data tracking paths:

  • Cockpit Loudspeaker Controls: Independent volume adjustment potentiometers are mounted on the outer edges of the glaresheld. These allow pilots to monitor active radio channels without wearing headsets during low-workload cruise flight.
  • Audio Interlock Relays: When a handmike or yoke PTT switch is toggled, an automatic loop back block silences the adjacent cockpit speakers to prevent acoustic feedback screaming across open flight deck microphones.