When observing engine performance, what should be monitored for signs of a cold start?

Monitoring engine performance for signs of a cold start is crucial for ensuring safe and optimal operation. When observing during a cold start, a gradual rise in N1 (the first stage compressor speed) accompanied by low ITT (inter-turbine temperature) indicates that the engine is progressing through its start cycle correctly. This behavior reflects the fact that the engine is in the early stages of operation where it is not yet generating significant heat, and it is expected for N1 to increase as the engine starts to spool up.

In this situation, low ITT suggests that the combustion process has not yet reached its operating temperature, which is typical during a cold start. This serves as an important safety and operational indicator, giving the pilot or technician insights into the engine's performance during initial startup.

The other scenarios would indicate different issues or conditions that are not typical of a proper cold start process. For instance, a stable N1 with increasing ITT might suggest that the engine is possibly not firing properly, while a rapid increase in N1 without an ITT change could indicate a malfunction. The focus on a gradual rise in N1 with low ITT is therefore the correct observation when assessing a cold start.