The A320 IDG: That Thing You Only Think About When It Quits

Hey - Simon here. Welcome to this week’s Bus Juice.

Today we’re looking at the electrical powerhouse of the A320, the IDG.

I know, I know, exciting… calm down.

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Most pilots (hopefully!) know the golden rule about the IDG disconnect button - three seconds max. But beyond that? The details start to blur, like the runway edges on a foggy morning.

Here’s what we’re covering:

• What an IDG actually is, how it works, and why you should care

• Common IDG issues

• Some associated ECAMs

• And more… (meaning a meme I thought was kinda funny)

Find the TLDR here

DEEP DIVE

What the HECK is an IDG anyway? 🤔

The Integrated Drive Generator (IDG) is the heart of your A320's electrical system, taking varying engine speeds and converting it into a steady electrical output for your aircraft's systems.

It consists of 4 key components:

• Constant Speed Drive (CSD): A hydraulic transmission system that maintains a steady output shaft speed of 12,000 RPM regardless of engine N2

• AC Generator: Attached to the CSD, creates 115V/400Hz three-phase AC electrical power

• Oil System: Serves dual purposes - cools/lubricates components and acts as the working fluid for the CSD's hydraulic control system

• Protection Systems: Monitor temperature, pressure, voltage, and frequency

How it all works:

1️⃣ Engine power transfers to the IDG via a drive shaft from the accessory gearbox

2️⃣ The CSD uses a hydraulic trim unit with planetary gears to maintain a constant output speed (very clever)

3️⃣ The generator produces up to 90 kVA of electrical power

4️⃣ Protection systems monitor parameters, and signal faults when limits are exceeded

Each A320 has two independent IDGs, one per engine, (durrr thanks Simon), providing redundancy in the electrical system.

The IDG can be disconnected from the engine in flight if necessary, but this is a one-way decision that requires maintenance intervention to reconnect on the ground.

Three Critical IDG ECAM Messages

1️⃣ ELEC IDG 1(2) OIL LO PR

What you'll see: On the ELEC page, "LO PR" appears in amber next to the IDG, and the IDG label changes from white to amber. 1 remains white if the engine is running.

What's happening: Your IDG oil pressure has dropped below 140 psi, affecting both lubrication and the hydraulic control system.

Common culprits:

• External oil leak (maybe visible during pre-flight)

• Internal seal failure (probably not visible during pre-flight)

• Oil pump wear

• Contaminated oil

• Blocked filter or pipelines

Helpful Hints:

This warning often serves as your early warning before a full failure.

Keep in mind that low pressure and high temperature are closely related - always watch for both.

The system suppresses this warning during low N2 operations, like engine start, to avoid false alarms.

Remember that the timeline from initial warning to actual fault can vary widely—from minutes to hours depending on severity.

Your response: 

✅ Follow ECAM procedures to disconnect the IDG. Press the IDG pb-sw until the GEN FAULT light comes on. But not for more than 3s!

✅ Monitor oil temperature trend

✅ Consider starting the APU

2️⃣ ELEC IDG 1(2) OIL OVHT

What you'll see: Temperature display on ELEC page:

• 147-185°C: Flashing green (early advisory)

• Above 185°C: Amber (overheat condition)

• Normal range: 70-110°C during cruise

What's happening: IDG oil temperature has exceeded safe operating limits—typically above 185°C.

Common culprits:

• Degraded cooling efficiency

• Internal mechanical issues generating excess heat

• Restricted oil flow

• Extended high-power operation

• Low oil quantity

• Seal failure letting hot engine air in

Helpful Hints:

This is serious and can rapidly lead to failure.

Keep in mind that rising temperature indicates potential mechanical damage occurring internally.

The IDG FAULT pushbutton will likely illuminate.

Disconnection is often required to prevent permanent damage to the system but auto disconnect will occur at 200°C.

The timeline from initial temperature warning to critical failure can accelerate quickly once the process begins.

Your response: 

✅ Following an advisory (see QRH) consider sheading load - GALLEY or GEN OFF

✅ Monitor temperature - stable or rising?

✅ Prepare for IDG disconnect if directed by ECAM

✅ Consider starting the APU

3️⃣ ELEC IDG 1(2) DISCONNECTED

What you'll see: On the ELEC page, "DISC" appears in amber below the IDG temperature, generator parameters show "OFF" in white, and the IDG label displays in amber.

What's happening: The IDG has physically separated from the engine, either:

• Manually (you pressed the button)

• Automatically (protection systems activated)

• Mechanically (connection failure)

Helpful Hints:

This condition is irreversible in flight, so maintenance will be required on the ground.

Remember that the affected generator is completely offline and cannot be recovered during flight.

The electrical system automatically reconfigures distribution to maintain essential power.

Monitor the remaining power sources carefully as you now have reduced redundancy in your electrical system.

Your response: 

✅ Verify bus tie has connected automatically

✅ Confirm affected AC bus is powered by remaining generator

✅ Start APU if available for redundancy

✅ Monitor remaining generator(s) load

A note about the MEL 📖

If despatching with an IDG inop you are limited to 33500ft.

As such if you have a failure in flight it might be worth considering a descent.

The reason for this is redundancy.

If you have a second failure, will the APU be able to cope?

The older FCOMs used to show a 90kVA limit at 33500ft and ISA.

Some food for thought…

MEME

The Meme Deck

Not sure I remember a tail wheel was mentioned during the type rating!?

TLDR

• IDGs convert variable engine speeds to constant electrical power

• Watch for: worn hydraulics, issues during idle descent, and cascading failures

• Remember the 3-second rule for disconnect button

• Know your ECAM for OIL LO PR, OIL OVHT, and DISCONNECTED

• Limited to 33,500ft with an IDG inop by MEL

• Always have a backup plan (APU) ready

Hope this helps!

Talk soon,

-Simon

^{Disclaimer - AKA don’t do dumb stuff and try and blame me}

^{This newsletter is intended for informational purposes only and should not replace official training materials, aircraft manuals, or company procedures. All information provided is based on publicly available sources and general operational knowledge. While every effort has been made to ensure accuracy, pilots should always refer to their company's Standard Operating Procedures (SOPs), Flight Crew Operating Manuals (FCOMs), Quick Reference Handbooks (QRHs), and Minimum Equipment Lists (MELs) for definitive guidance. The author and Bus Juice accept no responsibility for any actions taken based on this information. Always follow your company's policies and manufacturer's recommendations when operating an aircraft.}