The major components of the accessory gearbox are which two gear trains?

• A. N2 and N3
• B. N1 and N3
• C. N1 and N2
• D. N3 and N4

Answer: (C)

The part of the engine that powers accessories uses two separate gear trains, each tied to a different engine spool. These two gear trains are driven by the N1 and N2 spools. They provide the necessary reduction and torque to run all the accessories mounted on the gearbox, like pumps and starters. One train is connected to the low‑pressure spool (N1) and the other to the high‑pressure spool (N2), giving the gearbox drive across the engine’s speed range. In engines with other spools (N3, N4), those spools aren’t the two main accessory-drive paths, which is why N1 and N2 are the correct pair.