Which factor is critical to ensure safe operation during engine start-up?

Monitoring turbine inlet temperature is critical to ensuring safe operation during engine start-up because it provides vital information about the engine's thermal condition. During start-up, the engine transitions from ambient temperature to operational temperature, and the turbine inlet temperature helps in assessing whether the engine is operating within its safe thermal limits.

An excessively high turbine inlet temperature can indicate a malfunction or an issue such as improper fuel flow, leading to an increased risk of engine damage or failure. Conversely, proper monitoring helps ensure that the engine is starting correctly and that combustion is stable. This data is essential for the safe operation of the engine and helps to prevent incidents that could arise from overheating.

The other choices, while related to engine performance, do not directly influence safe operation as critically as turbine inlet temperature. For example, compressor air temperature can affect performance but does not provide the same immediate insights during start-up. Similarly, exhaust plume color and fuel injector performance are important for overall engine operation and efficiency but do not specifically indicate the safety parameters necessary during engine start.