How many stages of compression are in the engine's N1 section?

• A. Two
• B. One
• C. Three
• D. Four

Answer: (A)

N1 is the low‑pressure compressor part of a gas turbine engine, and its number of stages means how many times the air is boosted in pressure on the low‑pressure side before moving on to the next section. In this engine, the N1 section has two stages, so air is compressed twice by consecutive rotor/stator pairs within the low‑pressure compressor. This two‑stage design provides the needed pressure rise and flow characteristics at various operating speeds without making the LP compressor unnecessarily large or heavy. Air exiting N1 then enters the next compression stage (the high‑pressure side) for further boosting. If there were only one stage, the pressure rise would be smaller; with three or four stages, the LP compressor would be larger and heavier, which isn’t matching this engine’s design.