Cabin Interphone, Passenger Address and the CIDS

This article steps through the cockpit door to the cockpit↔cabin trio — cabin interphone, passenger address (PA) and the CALLS panel — and the cabin backbone that carries them all: the CIDS (Cabin Intercommunication Data System).

The crew do not need the CIDS the way a purser does, but four points matter: the CIDS is the common data hub for almost every cabin system (interphone, PA, signs, lighting, evacuation signalling, lavatory smoke), with dual-director redundancy; how the cockpit calls the cabin (the CALLS panel) and the cabin calls the cockpit (ATT/PRIO CAPT); how to make a passenger announcement; and where the crucial pre-flight CABIN READY memo comes from.

1. Architecture

        cockpit                              CIDS hub (dual director)
   ┌──────────────┐          ┌───────────────────────────────────┐
   │ ACP (CAB/PA) │──AMU────▶│  Director 1 (active)  Director 2   │
   │ cockpit      │          │  (hot standby); one fails → the    │
   │  handset     │          │  other takes over immediately      │
   │ CALLS panel  │──discrete▶│                                    │
   └──────────────┘          │  8 main-deck data-bus lines:       │
                             │   ├ 6 top lines ─▶ DEU A (pax)      │
                             │   │                along the cabin   │
                             │   └ 2 middle lines▶ DEU B (crew)     │
                             │                     near the doors    │
                             │  FAP + CAM (layout) + OBRM (software)│
                             └──────────────┬────────────────────┘
        cabin terminals ◀──────────────────┘
   loudspeakers · signs (NS/FSB/RTS) · reading lights · illumination · lavatory smoke
   AIP · AAP · Area Call Panel · handsets · passenger call buttons

Every cabin terminal hangs on two identical directors; if the active one fails the hot-standby one takes over immediately. Six top-lines serve passenger systems, two middle-lines serve crew systems; DEU A (Decoder/Encoder Unit type A) runs the passenger terminals along the cabin, DEU B sits near the doors for crew terminals. Change the cabin layout and you change only the CAM (layout database) plugged into the FAP — the hardware stays.

2. The CIDS — the cabin's central nervous system

The AMM states the CIDS's role. Per AMM 23-73-00:

The Cabin Intercommunication Data System (CIDS) is a microprocessor-based system. It operates, controls and monitors the main cabin systems and can do different system and unit tests. The connected systems are: Air conditioning, Communications, Fire protection, Ice protection, Lights, Water/waste.

From this chapter's view, the CIDS carries the string the FCOM lists. Per FCOM DSC-23-10-30:

The Cabin Intercommunication Data System (CIDS) provides signal transmission, control and processing for the following cabin systems: Cabin and service interphone; Passenger address; Passenger signs; Reading lights (LED technology); General cabin illumination; Emergency evacuation signalling; Lavatory smoke indication; Passenger entertainment system.

Its philosophy is "software-defined cabin": a layout change changes only the software database (CAM), not the hardware. Redundancy is by dual director. Per AMM 23-73-00:

Two functional units for the data bus control, the CIDS directors 1 and 2, One director in active mode and the second one in hot standby mode, Immediate switchover to the second director if a failure of the first one occurs.

3. CIDS topology — two directors, eight buses, DEU A/B

How the buses divide is the skeleton. Per AMM 23-73-00:

Eight data bus lines on the main deck (six top lines for passenger-related systems and the cabin illumination and two middle lines for crew-related systems).

The two DEU types hang on the two bus classes. Per FCOM DSC-23-10-30:

Decoder / Encoder Units (DEUs) linked to the two directors: Type A units (for passengers) installed along the cabin. The loudspeakers, lighted signs, call buttons, call lights and general illumination ballast units are divided into small groups, each connected to a type A DEU. Type B units (for attendants) installed near the exit doors. The Area Call panels, attendant handsets, slide / door pressure sensors, attendant indicator panels, are connected to type B DEUs.

One line: DEU A = passengers (along the cabin, top lines); DEU B = attendants (near the doors, middle lines). The FAP is the crew's control/monitor interface; plugged into it, the CAM holds the cabin layout and the OBRM holds the system software.

4. Cabin interphone and the CALLS panel — two-way calling

Cabin interphone links cockpit and attendant stations, initiated by the centre-pedestal CALLS panel (cockpit→cabin) and the attendant handset (cabin→cockpit).

Cockpit calls the cabin (CALLS panel). Per FCOM DSC-23-20-20:

FLT REST/CAB REST/PURS/FWD/MID/EXIT/AFT pb — When pressed: A steady pink lights come on, on the corresponding area call panel; 'CAPTAIN CALL' message appears on the corresponding AIP, and a green light comes on; A high-low chime sounds through corresponding loudspeaker.

The ALL key calls all attendant stations; the guarded EMER key is for emergency. Per FCOM DSC-23-20-20:

EMER pb-sw (GUARDED) — When pressed: A pink lights flash on all area call panels; 'CALL PRIO CAPT' message appears on all AIPs, and a red light comes on; A high-low chime is repeated three times through all loudspeakers.

Cabin calls the cockpit (attendant handset): the CAPT key gives ATT light + buzzer on the ACP; the PRIO CAPT key (emergency) gives ATT + three buzzers. One key inhibition. Per FCOM DSC-23-20-20:

[CAPT key] In the cockpit, the 'ATT' lights up on the ACP, and a buzzer sounds. [...] The buzzer is inhibited during takeoff and landing.

[!note]- A routine call chimes once, an emergency call three times; the buzzer is inhibited on take-off/landing The count encodes urgency: a routine CAPT = one chime/buzzer, an emergency PRIO CAPT / EMER = three. The routine buzzer is inhibited on take-off/landing (critical-phase silence, like SELCAL in article 4), but the EMER level is not. Hear "three in a row" and it is the cabin reporting something urgent.

5. Passenger address

For announcing to passengers, the FCOM gives the entry. Per FCOM DSC-23-20-40:

The passenger address system allows flight personnel to make passenger announcements in the cabin via the loudspeakers. It can be operated from the cockpit (with ACP, or handset), or from the cabin (attendant stations).

The cockpit has two paths: the ACP PA transmit key (article 3: spring-loaded, must be held) plus a microphone; and the cockpit handset at the bottom of the pedestal, which announces without touching the ACP. Per FCOM DSC-23-20-40:

Note: The flight crew may use a cockpit handset to make PA announcements without action on the ACPs.

PA is priority-ranked (announcement over entertainment music, crew over pre-recorded); picking up the cockpit handset is the fastest way to broadcast.

6. CABIN READY — the pre-flight memo

The most important memo the CIDS sends the cockpit is the pre-take-off/landing cabin-ready signal. Per FCOM DSC-23-49:

CABIN READY — This memo indicates to the flight crew that the cabin is ready for take-off or for landing. This memo appears when the cabin crew presses the 'CABIN READY' key on the FAP.

Companions are CABIN...CHECK (in the take-off/landing memo checklist, meaning the cabin is not ready — CABIN READY not pressed on the FAP) and VIDEO IN USE (a pre-recorded IFE video announcement in progress).

[!note]- CABIN READY is a digital cabin-to-cockpit handshake Cabin readiness used to come by handset/chime and a spoken report; the CIDS digitises it into a memo — the purser presses CABIN READY on the FAP, and the cockpit ECAM shows CABIN READY (or CABIN...CHECK disappears from the take-off/landing checklist). This is the source of the "CABIN … READY" checklist item (article 11).

Self-test

[!note]- Q1. Which classes of cabin system does the CIDS carry, why can the layout change without changing hardware, and how do the two directors give redundancy? Interphone, PA, signs, reading lights, illumination, evacuation signalling, lavatory smoke, entertainment. Layout is software-defined (the CAM). One director active, one hot standby, with immediate switchover.

[!note]- Q2. How do the eight buses divide, and what do DEU A and DEU B each connect and where? Six top lines (passengers) + two middle lines (crew). DEU A = passenger terminals along the cabin; DEU B = crew terminals near the doors.

[!note]- Q3. Cockpit presses FWD, ALL, then EMER — how does the cabin respond to each? FWD: steady pink light + CAPTAIN CALL on the AIP + high-low chime at that station. ALL: all stations respond. EMER (guarded): flashing pink on all, CALL PRIO CAPT red, chime three times on all.

[!note]- Q4. CAPT versus PRIO CAPT key from the cabin — how many buzzers in the cockpit, and why is the routine buzzer inhibited on take-off/landing but not EMER? CAPT = one buzzer, PRIO CAPT = three. The routine buzzer is inhibited in critical phases; the emergency level is not.

[!note]- Q5. What are the cockpit's two PA paths, and which is fastest? Who triggers CABIN READY and how? ACP PA key + microphone, or the cockpit handset (without the ACP — fastest). The purser triggers CABIN READY by pressing it on the FAP.

Key takeaways

Point	Detail
CIDS	Dual director (1 active / 1 hot standby); 8 buses (6 passenger / 2 crew); DEU A pax / DEU B crew; software-defined layout
CALLS panel	Cockpit→cabin FLT REST…/ALL/EMER (guarded); cabin→cockpit CAPT (one) / PRIO CAPT (three)
Buzzer inhibit	Routine cabin-call buzzer inhibited on take-off/landing; EMER not
PA	ACP key (hold) or cockpit handset (no ACP, fastest)
CABIN READY	Purser presses it on the FAP → cockpit memo; source of the checklist item

References

FCOM DSC-23-10-30 — CIDS systems carried, dual director, DEU A/B, FAP/AIP/AAP/Area Call Panel.
FCOM DSC-23-20-20 — CALLS panel (cockpit→cabin FLT REST…/ALL/EMER), cabin→cockpit CAPT/PRIO CAPT, buzzer inhibit.
FCOM DSC-23-20-40 — PA (ACP or handset); cockpit handset without the ACP.
FCOM DSC-23-49 — CABIN READY / CABIN...CHECK / VIDEO IN USE memos.
AMM 23-73-00 — CIDS microprocessor hub, software-defined layout, 8 buses (6 top/2 middle), dual-director hot-standby switchover.

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.