The major components of the accessory gearbox are the ______ gear train and the ______ gear train.

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

Answer: (A)

The thing being tested is how the accessory gearbox gets power from the engine spools. In a typical two-spool engine, the accessory gearbox contains two independent gear trains: one driven by the N1 spool and one driven by the N2 spool. These two gear trains are the pathways that reduce the high speeds of the engine spools to the slower, usable speeds needed by accessories such as pumps, generators, and starter gear. The N2 gear train is the primary drive for most accessories, while the N1 gear train provides a secondary drive path that ensures accessories can be powered from either spool or provide backup as conditions require. That dual-gear-train arrangement is why the major components of the accessory gearbox are described as the N1 gear train and the N2 gear train. The other options pair spools (like N3 or N4) that correspond to different engine configurations and aren’t part of the standard two-spool AGB description.