What does a hung start indicate?

A hung start indicates a situation where there is a rapid increase in Interstage Turbine Temperature (ITT) without the engine achieving ignition. This condition typically occurs during the startup phase of a gas turbine engine when fuel is introduced, but the ignition process fails to happen as expected.

In a successful engine start, the fuel should ignite, leading to a proper rise in engine RPM and a stable ITT as the engine approaches operational parameters. However, if ignition does not occur, the temperature can continue to rise due to the injection of fuel, which can lead to potential damage if not addressed promptly. This scenario signals operators to investigate and rectify the underlying issue, ensuring the ignition system or fuel flow is functioning correctly.

Understanding this concept is critical in aviation and power generation contexts, where engine reliability and safety are paramount. This is why the rapid increase in ITT without ignition is the hallmark of a hung start.