Communication Abnormals and Degradation

This article gathers the chapter's degradation strand — from handling a single ECAM alert, to the "only emergency power" communications inventory, to the "total loss of communication" continuation. Communication abnormals share a general character: most are Level 1/2 "crew awareness", rarely a red warning — because a communications failure does not directly imperil the aircraft, but affects the link to ATC, cabin management and the accident record. So the skill is knowing "what is left when it fails, and how to work around it".

The chapter's ECAM communication alerts live in PRO-ABN-COM (datalink-application-layer alerts are in PRO-ABN-DATALINK, ATA-46).

1. The ECAM communication alert family (PRO-ABN-COM at a glance)

2. The CIDS fault family — total loss versus PA alone

The CIDS is the cabin communications hub (article 7); its total loss is the widest-reaching communications fault. Per FCOM PRO-ABN-COM:

This alert triggers when there is a total loss of CIDS.

The consequence, per FCOM PRO-ABN-COM:

Passenger address, cabin and flight crew interphone, service interphone, passenger signs, and communication with the lower deck and flight crew rest compartment are inoperative.

[!warning]- CIDS total loss = the cabin goes mute Both directors lost (article 7's dual-director hot standby means a single failure switches over silently and does not raise this alert; this alert means both are gone) — PA and interphone between cockpit and cabin are both dead, and the signs go dark. Cockpit-to-cabin coordination falls back to the most basic means (face-to-face, prearranged signals). By contrast COM CIDS PA FAULT is only PA or cabin interphone degraded — far smaller reach. A textbook case of "read the alert name to judge the reach": 1+2 FAULT (total) >> PA FAULT (single item).

3. The stuck-PTT family — SINGLE PTT STUCK and VHF/HF EMITTING

A PTT stuck in transmit occupies a frequency continuously and blankets the whole channel — the most "neighbour-disturbing" communications fault. COM VHF/HF EMITTING (VHF transmit > 30 s or HF > 60 s) — first try to unstick. Per FCOM PRO-ABN-COM:

1. If any Push To Talk (PTT) transmission selector (sidestick PTT, PTT hand mike, or ACP PTT switch) is jammed in the transmit position, try to release it in order to remove the caution. 2. If unsuccessful, deselect the identified failed VHF/HF transmission keys on the associated Audio Control Panel (ACP) to remove the caution. This ACP should only be used in reception mode. The associated PTT transmission selectors must not be used.

COM SINGLE PTT STUCK (PTT stuck > 40 s VHF / > 180 s HF) — locate the faulty ACP (procedure steps):

DURING 20 s:
  ALL PTT ............................ CHECK RELEASED
  ACP1 VHF/HF TX ..................... DESELECT
  IF UNSUCCESSFUL: ACP2 VHF/HF TX .... DESELECT
  IF UNSUCCESSFUL: ACP3 VHF/HF TX .... DESELECT
Once the ACP linked to the stuck PTT is identified, the ECAM actions become:
  AUDIO SWTG ......................... DO NOT USE
  affected ACP, ALL TX KEYS .......... DO NOT USE
  all other ACP, TX KEYS ............. AS RQRD

(FCOM PRO-ABN-COM, COM SINGLE PTT STUCK)

[!warning]- Why "AUDIO SWTG DO NOT USE" once the stuck PTT is located The chain: a stuck PTT belongs to one ACP → you must isolate that ACP (all its transmit keys DO NOT USE, use another ACP for tx/rx). If you now used AUDIO SWITCHING (article 3) to route audio to the third channel, you could carry the faulty ACP's fault across, or defeat the isolation — so the procedure states "AUDIO SWTG DO NOT USE". This is the opposite of the everyday "ACP failed → use AUDIO SWITCHING to recover" (article 3): that is an ACP that has failed (not transmitting), this is a PTT that is stuck (transmitting continuously) — the former borrows a channel, the latter isolates one. Seeing "not transmitting versus over-transmitting" is the key to choosing the right handling. The unaffected side's ACP may recover the deselected VHF/HF channel (the EMITTING alert's note).

4. Audio channel failure and AUDIO SWITCHING

When ACP 1 or 2 (or the corresponding AMU channel) fails (does not transmit), use AUDIO SWITCHING to borrow the third channel (article 3, §7): CAPT ON 3 = the captain uses the third occupant's ACP; F/O ON 3 = the first officer does. The cost is the third occupant losing access. Note the contrast with §3 (see the callout above).

5. RMP failure

A single RMP fails → displays go black → switch it OFF (letting the upstream RMP take over transparently, article 2's leader priority); two fail → one controls all. Operating action in article 11 §8.

6. The emergency-electrical communications inventory

The thread planted in article 1 closes here: after a total loss of main generation, on emergency electrical power, communications keep only "one of each kind":

So emergency-power communications = RMP 1 + VHF 1 + HF 1 + the number-1 ACP — just enough to talk to ATC. Same "keep the number-1 side" philosophy as the electrical chapter's EMER ELEC margin and the navigation chapter's emergency-navigation margin (ATA-24).

7. Total loss of communication

When no voice means can establish contact with ATC (all equipment lost, or all frequencies tried without result): apply the loss-of-communication procedure — set the transponder to 7600 (radio failure), continue per the received clearance/expected routing, and if available relay via other aircraft or attempt SATCOM/CPDLC. The airborne/IFR communication-failure rules (altitude, routing, approach choice) are regulatory and link out to regulations (CCAR / ICAO Annex 10 / Doc 4444 communication-failure procedures).

[!note]- Closing mental map: the three lines of retreat in communications degradation (1) single system fault (an ECAM COM alert) → isolate/work around per PRO-ABN-COM; voice usually remains; (2) electrical degradation (EMER ELEC) → retreat to RMP 1 + VHF 1 + HF 1 + ACP 1, still able to reach ATC; (3) total loss → 7600 + regulatory procedure. Each retreat leaves fewer means but a floor. Hold these three lines and any communications fault can be placed: "which line am I on, and what remains".

Self-test

[!note]- Q1. What does COM CIDS 1+2 FAULT knock out, why does a single director failure not raise it, and how does it differ from CIDS PA FAULT? PA, cabin/flight/service interphone, passenger signs, lower-deck/rest comms. A single director switches over silently (dual hot standby). CIDS PA FAULT is only PA/cabin interphone degraded — far smaller reach.

[!note]- Q2. SATCOM DATA FAULT, SATCOM VOICE FAULT, SATCOM FAULT — what is lost and what remains in each? DATA FAULT: ACARS inop, telephone remains. VOICE FAULT: telephone inop, ACARS still via SATCOM. FAULT: both inop.

[!note]- Q3. Once a stuck PTT is located on an ACP, why is AUDIO SWITCHING then "do not use", and why is this opposite to "ACP failed → use AUDIO SWITCHING"? You must isolate the faulty ACP; AUDIO SWITCHING could carry the fault across or defeat isolation. A failed ACP (not transmitting) borrows a channel; a stuck PTT (over-transmitting) isolates one.

[!note]- Q4. What four items make up the emergency-power communications inventory, and why do they survive? RMP 1 + VHF 1 + HF 1 + the number-1 ACP — all fed from the essential network.

[!note]- Q5. What transponder code for total loss of communication, and where do the detailed rules live? 7600; the detailed rules are regulatory (CCAR / ICAO Annex 10 / Doc 4444).

Key takeaways

References

• FCOM PRO-ABN-COM — CIDS/PA/HF-SATCOM-VHF3 DATA faults, SINGLE PTT STUCK, VHF/HF EMITTING handling.
• FCOM DSC-23-10-20 / -30-10 — RMP 1 / VHF 1 / HF 1 as EMER ELEC survivors (degradation inventory).
• FCOM DSC-23-10-30 / -50 — AUDIO SWITCHING, RMP failure handling.
• FCOM PRO-ABN-DATALINK (ATA-46) — ATC COM VOICE ONLY / ATSU FAULT (datalink application layer; this chapter only points there).

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; §7 total-loss details follow regulations and the operator's manuals.