Engine Vibration — Vibration System, the EIVMU Name Revealed, N1/N2/N3 VIB

Engine Indicating shows VIB N1/N2/N3 on the ENG SD. This article covers the vibration-monitoring system itself, and reveals the EIVMU name: when 02/11 described the FADEC interface, the FCOM gave only "Engine Interface Unit (EIVMU/EIU)" and the "VM" was deferred to here, against AMM-77 — now resolved.

1. Vibration-system components

The engine vibration system comprises per engine: ‐ one vibration transducer ‐ one vibration junction box ‐ one RCC (Remote Charge Converter) ‐ one EIVMU (Engine Interface and Vibration Monitoring Unit) ‐ one once per Rev sensor (N1).

Per AMM 77-30-00, per engine: one vibration transducer, one junction box, one RCC (Remote Charge Converter), one EIVMU (Engine Interface and Vibration Monitoring Unit), and one once-per-rev sensor (N1).

[!note]- Paying off the EIVMU-name debt from 02/11 When 02/11 described the FADEC interface, FCOM DSC-70-20 wrote only "Engine Interface Unit (EIVMU/EIU)" and the "VM" was left unexpanded, deferred to here against AMM-77. AMM 77-30-00 verbatim reveals: EIVMU = Engine Interface and Vibration Monitoring Unit. So the EIVMU wears two hats: ① engine interface (forwarding aircraft data to the FADEC, 02) + ② vibration monitoring (this article).

2. Signal chain

Monitoring is performed by a vibration transducer on each engine. This produces electrical signals in proportion to the vibration detected. Electrical signals are sent from the vibration transducer to the RCC (Remote Charge Converter) through the vibration junction box. The signal is then amplified...

Per AMM 77-32-00:

 vibration transducer → junction box → RCC → EIVMU (amplify/monitor) → ENG SD (VIB N1/N2/N3)
 once-per-rev sensor (N1) ──────────────────────┘ (speed reference)

The transducer produces electrical signals proportional to the detected vibration, sent via the junction box to the RCC, then amplified.

3. VIB N1/N2/N3 display

N1, N2, N3 VIBRATIONS — The vibration of the LP(IP)(HP) rotor is in normal range. The level of LP(IP)(HP) rotor vibration is excessive.

Per DSC-70-90-40, the ENG SD shows VIB N1/N2/N3 for the LP/IP/HP rotors (01), in two states — normal / excessive (no precise numeric threshold is given here).

High vibration is often associated with FOD/bird strike (28), bearing wear (05 chip detector), blade damage, severe damage (30).

4. Counterintuitive point

[!warning]- The EIVMU wears two hats (interface + vibration monitoring) EIVMU = Engine Interface and Vibration Monitoring Unit (AMM-77-30-00) — both forwarding aircraft data to the FADEC (02) and doing vibration monitoring (this article). Earlier it appeared as just an "interface unit" because the FCOM description gave only half the name.

Self-test

[!note]- Q1. The vibration-system components per engine? 1 vibration transducer + 1 junction box + 1 RCC + 1 EIVMU + 1 once-per-rev sensor (N1).

[!note]- Q2. What does EIVMU stand for? Engine Interface and Vibration Monitoring Unit — two hats (interface + vibration monitoring).

[!note]- Q3. Which rotor is each of VIB N1/N2/N3? N1 = LP (fan), N2 = IP, N3 = HP.

[!note]- Q4. How many display states? normal / excessive (no precise numeric threshold given here).

Key takeaways

References

• AMM 77-30-00 §3 — vibration-system components + EIVMU = Engine Interface and Vibration Monitoring Unit.
• AMM 77-32-00 §3 — vibration signal chain: transducer → junction box → RCC → amplified.
• FCOM DSC-70-90-40 (10) — VIB N1/N2/N3 display, normal/excessive.

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.