What indicates a hung start during engine start?

A hung start refers to a condition during the engine start sequence where the engine starts, but fails to reach the normal operating parameters, particularly N1 (fan speed) and N2 (high-pressure compressor speed). When N1 or N2 fails to stabilize and remains at a low level despite the start sequence progressing, it indicates that the engine is not performing as expected. This can happen if the ignition occurs but the engine does not develop enough thrust or speed, resulting in a halted start.

In contrast, oil pressure below limits immediately indicates issues related to lubrication and engine health, while fluctuating ITT (Inter Turbine Temperature) during start might suggest other issues but does not specifically denote a hung start. Fuel flow discontinuity, although problematic, also does not directly correlate with the definition of a hung start. Being able to identify a hung start promptly is crucial for safety and operational protocols, enabling the crew to take appropriate corrective actions.