Communications Overview and the Audio-Integrating Architecture

If the navigation chapter (ATA-34) is the aircraft's senses, the communications chapter (ATA-23) is its nerves and voice: how the crew talk to each other, to the cabin, to the ground engineer, to ATC and the company; how announcements reach the passengers; and how the aircraft records all of it. ATA-23 produces no flight data — it is the channel for every voice and every call between people, the aircraft, and the outside world.

This chapter has an unusual character: many boxes, simple logic. The hard part is not how any single transceiver works — it is how a heap of radios, interphones, a public-address system and a recorder are integrated into the two small panels the crew actually touch. So this first article raises two pillars before diving into any one box: the whole-chapter map, and the audio-integrating concept — the key that unlocks the rest of the chapter. Learn one sentence — the RMP chooses the frequency, the ACP chooses the station and whether you transmit or receive — and every later article is just another box hanging off that skeleton.

1. The chapter's purpose and the maintenance taxonomy

The maintenance manual states the purpose plainly. Per AMM 23-00-00:

The communication system allows crew members to communicate with each other, from the cockpit and from the ground. They can also communicate with the passengers, other aircraft and the ground stations.

Count the "who to whom" in that sentence: crew-to-crew, crew-to-ground, crew-to-passengers, aircraft-to-aircraft, aircraft-to-ground-station. Five audiences, and each maps to a class of hardware — interphones (within the crew), the ground-crew call and service interphone (crew to ground personnel), the PA (crew to passengers), and VHF/HF/SATCOM (aircraft to the outside world). The AMM realises these as functional families (§A radio communication, §B data transmission, §E audio integrating, §F static discharger, §G audio-video monitoring — CVR/CDSS/CIDS, §H integrated automatic tuning — RMP, §J data-bus communication — CCS). The flight-crew-relevant families are voice communication, audio integrating, frequency management, interphone/PA/CIDS, CVR, door surveillance, ELT and the static dischargers. The passenger in-flight-entertainment family (music, video, PATS, AM/FM) is a cabin and maintenance layer and is not covered here — not because it is unimportant, but because it is not flight-crew mechanism, and forcing it in would only dilute the depth.

2. The FCOM's three-way split — internal, external, emergency

The FCOM, written for the crew, re-cuts the same hardware by where it communicates to. Per FCOM DSC-23-10-10:

The communication system enables: Internal communication between the: Flight crew and additional cockpit occupant(s), Cabin crew, Ground crew, Passengers. Internal communication is possible via the flight, cabin, and service interphones, and via the Passenger Address (PA). External communication via radio communication (HF or VHF) or Satellite Communication (SATCOM), either in voice mode or data mode.

• Internal (articles 6, 7): flight, cabin and service interphones, and the PA;
• External (articles 4, 5): HF, VHF and SATCOM — each usable in voice or data mode;
• Emergency (FCOM DSC-23-40, articles 8, 9): evacuation signalling, cockpit alerting (anti-hijack) and the ELT.

Hold on to that voice-or-data dichotomy — it is the root of a whole family of later rules: VHF 3 normally carries data (do not casually use it for voice), HF has a datalink, and SATCOM offers voice and data channels in parallel.

3. Audio integrating — the key to the whole chapter

The FCOM immediately gives the three subsystems that form the skeleton. Per FCOM DSC-23-10-10:

The communications system comprises the following subsystems: VHF / HF transceivers, Radio tuning systems (Radio Management Panels), Audio integrating system (Audio Management Unit, Audio Control Panels).

Make the division of labour explicit and the chapter stands up:

1. Transceivers (VHF/HF/SATCOM) — the boxes in the avionics bay that actually radiate and receive; the crew never touch them;
2. RMP — radio tuning (article 2): decides what frequency each transceiver is set to. It manages frequency, not transmit/receive;
3. Audio integrating — AMU + ACP (article 3): decides which station I am using and whether I am listening or talking. The AMU is the switchboard behind the panel; the ACP is the keyed panel in front of the crew.

The AMM's definition of audio integrating is the fullest. Per AMM 23-00-00:

The audio integrating system integrates and allows easy selection of all audio signals (audio outputs, microphone inputs, sidetone and push-to-talk) produced by and feeding the radio communication and radio navigation systems. The system also provides SELCAL, part of call and flight interphone functions.

"Integrates" is the operative word: the crew never re-patch a headset between VHF 1, VHF 2 and HF 1. They press "VHF 1 receive" or "HF 1 transmit" on one ACP, and the AMU routes the microphone, headset, sidetone and PTT to the right station behind the scenes. The A330 abstracts "a dedicated transmit/receive control per radio" into "choose frequency (RMP) + choose station and transmit/receive (ACP)" — two panels for everything. Learn that abstraction and every device in articles 4–7 becomes simply "another audio source hung on the AMU".

[!warning]- The RMP does not transmit; the ACP does not tune The commonest confusion: pressing VHF 1 on the RMP does not let you talk on VHF 1. It does not. The RMP only sets VHF 1 to a frequency; to listen or speak you go to the ACP and press VHF 1's reception knob / transmission key. Frequency (RMP) and transmit/receive (ACP) are two separate things on two separate panels. This division is the bedrock of the chapter.

4. The physical radios that carry the datalink, and the ATSU boundary

All three external radios can carry data. Where the data goes, and what happens when it cannot, the AMM states plainly. Per AMM 23-00-00:

...These data are transmitted through the VHF 3 system (or through the SATCOM system if installed).

The FCOM completes the switching logic in the SATCOM section. Per FCOM DSC-23-30-20-10:

ACARS or ATSU communications normally transmit via VHF 3. They automatically switch to SATCOM when VHF 3 is not available.

This draws the chapter's single most important boundary:

[!warning]- Boundary: the datalink "pipe" is ATA-23, the "content" is ATA-46 The physical radios (VHF3-data, HF-data, SATCOM-data) belong to this chapter — they are the datalink's pipes. But the datalink application layer — the ATSU (Air Traffic Service Unit), CPDLC, AOC, FANS and the DCDU display — lives in ATA-46 Information Systems (FCOM DSC-46-10) and DSC-22 (MCDU). This chapter teaches the pipe, not the messages that run through it. The one exception is the RMP LOAD function (article 2): ATC sends a frequency by datalink, the ATSU validates it, and the crew load it into the standby window with one key press — the single deep interface between the datalink and this chapter's hardware. Everything else datalink links out to ATA-46. This split follows Airbus's own ATA taxonomy (23 = communications hardware and voice; 46 = information systems / data application).

5. Static dischargers — keeping communications and navigation legible

Why does a row of small wicks on the wingtips belong to a communications chapter? The AMM gives the cause and effect. Per AMM 23-00-00:

During flight the aircraft can become charged with static electricity. If the discharge of this static electricity is not controlled, it can cause interference in the communications and navigation systems. Static dischargers are installed on the aircraft to decrease the interference.

The mechanism: flying through cloud, precipitation or dust charges the airframe (precipitation static, "p-static"). If that charge coronates uncontrolled from wingtips and trailing edges, it radiates broadband RF noise that swamps VHF/HF reception and the VOR/ADF identification audio — the crew hear a hiss on the radios and see the ADF needle wander. The static dischargers (discharge wicks) on the wing, tail and control-surface trailing edges bleed the charge back to the atmosphere in a fine, weak, spectrally-concentrated way so the discharge does not land in the communications band. That is why a structural item lives in the communications chapter: its customer is communications and navigation signal quality (navigation side: ATA-34-06).

6. The spectrum basis — HF skywave, VHF line-of-sight, SATCOM satellite

The physical difference between the three external radios is worth fixing once (detail in articles 4 and 5). Per AMM 23-10-00:

[HF] Two transceivers and associated equipment allow long range voice communications within 2.8 to 23.999 MHz frequency range, with 1KHz spacing. In DATA mode, they operate within 2 to 29.999 Mhz frequency range, with 100 Hz channel spacing.

[VHF] Three transceivers and associated equipment allow short range voice communications within 118 to 136.975 MHz frequency range with 8.33 KHz spacing.

• HF (2.8–24 MHz) reflects off the ionosphere (skywave) for beyond-line-of-sight reach — the pre-satellite means of crossing oceans, and still SATCOM's backup;
• VHF (118–137 MHz) travels line-of-sight, covering roughly 200 nm — the workhorse over land;
• SATCOM (L-band, ~1.5 GHz) relays via geostationary satellites, covering the globe except the poles (article 5).

One line to remember: HF bounces the ionosphere for range, VHF runs straight for the near field, SATCOM goes up to the satellite for global cover. Their coverage differences directly drive the "which one for which phase" logic in article 11.

7. The emergency-electrical communications inventory

A single thread runs the length of this chapter: after a total loss of main generation, on emergency electrical power (EMER ELEC CONFIG), communications keeps only one of each kind. Three FCOM lines pin the three classes:

Per FCOM DSC-23-10-20: Only RMP1 functions in EMER ELEC CONFIG.

Per FCOM DSC-23-30-10: Only VHF1 operates in EMER ELEC CONFIG.

Per FCOM DSC-23-30-10: Only HF1 is supplied in EMER ELEC CONFIG.

So the emergency communications inventory is RMP 1 (tuning) + VHF 1 (short range) + HF 1 (long range) + the number-1 ACP — just enough to talk to ATC. This is one face of the same "keep the number-1 side" philosophy as the electrical chapter's emergency survivors and the navigation chapter's emergency-navigation inventory (ND 1, FMGC 1, VOR 1, DME 1 …). Article 12 gathers this inventory into the complete communications-degradation picture.

8. Configuration baseline

Optional-equipment content in this material follows the configuration summary some operators carry in the QRH operational data, cross-checked against the FCOM section applicability and the AMM. The configuration covered here is:

Self-test

[!note]- Q1. How does the FCOM split communications into three classes, and what does "internal communication" comprise? Internal / external / emergency. Internal = flight, cabin and service interphones plus the PA. External = HF, VHF, SATCOM, each in voice or data mode. Emergency = evacuation signalling, cockpit alerting and the ELT.

[!note]- Q2. What does "audio integrating" integrate? What does the RMP manage versus the ACP? It integrates all audio outputs, microphone inputs, sidetone and PTT of the radios and nav receivers into one selection surface. The RMP manages frequency; the ACP manages which station and transmit/receive. Pressing VHF 1 on the RMP does not let you transmit.

[!note]- Q3. ACARS/ATSU data normally routes via which radio, and where does it switch when that is unavailable? Normally VHF 3; it automatically switches to SATCOM when VHF 3 is not available.

[!note]- Q4. Why is the datalink not fully in this chapter? What does this chapter manage and not manage, and what is the single exception? The physical radios (pipes) are ATA-23; the ATSU/CPDLC application layer is ATA-46. The one deep interface is the RMP LOAD function (loading an ATSU-validated ATC frequency).

[!note]- Q5. Why is a structural item — the static discharger — in the communications chapter? Because uncontrolled airframe static discharge radiates RF noise into the communications and navigation bands; the dischargers bleed the charge off cleanly to protect signal quality.

[!note]- Q6. What communications survive on emergency electrical power, and why those? RMP 1 + VHF 1 + HF 1 + the number-1 ACP — all fed from the essential network — just enough to talk to ATC. Same "keep the number-1 side" philosophy as ATA-24/34.

Key takeaways

References

• FCOM DSC-23-10-10 — communications overview: internal/external split, the three subsystems.
• FCOM DSC-23-10-20 / DSC-23-30-10 — RMP 1 / VHF 1 / HF 1 as EMER ELEC survivors.
• FCOM DSC-23-30-20-10 — ACARS/ATSU via VHF 3, switching to SATCOM.
• AMM 23-00-00 — chapter purpose, functional families, audio-integrating definition, static dischargers.
• AMM 23-10-00 — HF and VHF frequency ranges and channel spacing.

Independent study material, not an Airbus publication and not endorsed by the manufacturer. Always defer to the current operator FCOM, FCTM, and QRH for operational use.