The N2 displays on a gray background until the engine is ______.

The N2 displays on a gray background until the engine is ______.

• A. Stable
• B. Running
• C. Starting
• D. Off

Answer: (A)

During engine start, certain indications use a gray background to show the value isn’t yet valid. N2 is the speed of the high‑pressure spool, and you can’t rely on its reading until the engine is in a stable operating condition. Once the engine reaches a stable N2 (within the normal idle/running range and not fluctuating), the indication becomes valid and the display returns to its normal color. So the gray background stays until stability is achieved, which is why the correct fill is that the engine is stable.

During engine start, certain indications use a gray background to show the value isn’t yet valid. N2 is the speed of the high‑pressure spool, and you can’t rely on its reading until the engine is in a stable operating condition. Once the engine reaches a stable N2 (within the normal idle/running range and not fluctuating), the indication becomes valid and the display returns to its normal color. So the gray background stays until stability is achieved, which is why the correct fill is that the engine is stable.