During start, which parameter is a critical limit to avoid engine damage?

• A. Oil viscosity.
• B. Ambient humidity.
• C. Maximum allowable EGT during start.
• D. Color of exhaust.

Answer: (C)

During start, the critical limit is the maximum allowable exhaust gas temperature. This temperature reflects the thermal load the turbine components can safely handle. If EGT rises beyond the limit, the blades and hot sections can overheat, leading to thermal damage, accelerated wear, or even failure. The start sequence is designed to keep fuel delivery and rotation within a safe EGT window, using the EGT limit as the primary safeguard.

Oil viscosity matters for lubrication and bearing health, but it doesn’t provide a direct, immediate limit to prevent damage during start. Ambient humidity and the color of exhaust aren’t reliable metrics for protecting the engine in the start transient, and they do not define a sharp damage threshold like EGT does.