Definition
An aircraft electrical power unit that combines a constant-speed drive (CSD) and an AC generator into a single sealed assembly. The CSD portion uses a hydromechanical transmission to convert the engine's variable-speed accessory drive output into a constant rotational speed, which then turns the generator to produce AC power at a stable frequency (typically 400 Hz).
Plain English
A single packaged unit, driven by the engine, that produces steady AC electrical power for the aircraft regardless of how fast the engine is turning.
Context Anchor
Seen in turbine aircraft electrical-system descriptions, cockpit electrical indications, and maintenance procedures for engine-driven power sources.
Derivation
Integrated means combined into one unit. Earlier aircraft used a separate constant-speed drive bolted to a separate generator. Putting both into one sealed housing made the package smaller, lighter, and easier to maintain — hence integrated drive generator.
Why Pilots Care
It supplies reliable constant-frequency power to avionics, flight instruments, and other critical systems, avoiding interruptions that could compromise safety or navigation.
Intuition Check
Do not read this as just “a generator installed in the airplane.” The important idea is that the speed-control drive and the generator are built into one assembly.
Example Sentence 1
After the left engine's IDG showed a high oil temperature, the crew disconnected it and continued on the right generator and APU.
Example Sentence 2
If the Integrated Drive Generator overheats in flight, the crew follows the procedure to disconnect it and switch to the backup generator.