What is the first sign of a potential problem in a gas turbine engine during startup?

The first sign of a potential problem in a gas turbine engine during startup is typically observed as a lack of RPM increase with engine ignition. During the startup sequence, the engine is expected to reach a certain RPM as the ignition system engages and the combustion process begins. If there is no increase in RPM, it indicates that the engine is not responding correctly to the start command, which could point to issues such as a malfunctioning ignition system, fuel delivery problems, or other mechanical failures that are preventing the engine from beginning the combustion process.

Observing no RPM increase can serve as an early warning for technicians to investigate and address the issue before proceeding, as it may prevent further complications or damage to the engine. In contrast, while excessive smoking or immediate shutdowns are also signs of potential problems, they generally occur after some initial operation has begun. No fuel flow detected is a critical issue but is often checked prior to the attempt to start the engine. Hence, the lack of RPM increase stands out as the first indicator during the initial startup phase.