What happens to Np during a hung start?

During a hung start, the indication of Np (the engine speed of a gas turbine) is typically stable or shows no significant indication of change. This is because a hung start occurs when the engine starts but does not reach the required RPM level for it to ignite and operate properly. Instead of accelerating, the Np may remain at low RPM without fluctuations, as the engine does not gain the necessary power from the combustion process to increase its speed.

In contrast, the other choices imply varying behaviors of Np, which do not accurately reflect the nature of a hung start scenario. The key aspect of a hung start is the engine's inability to progress through the start sequence, leading to a stable but low reading of Np. Understanding this helps in diagnosing engine start issues and ensuring that the correct procedures are followed during engine operations.