FAA Powerplant Written Practice Test

If stress rupture cracks are found on the leading edge of a first stage turbine blade, what condition should be suspected?

1. Excessive vibration

2. Over-temperature condition

3. Improper blade alignment

4. Residual stress from manufacturing

The correct answer is: Over-temperature condition

When considering the presence of stress rupture cracks on the leading edge of a first-stage turbine blade, the condition most closely associated with this phenomenon is an over-temperature condition. Turbine blades in jet engines are subject to extreme temperatures and stresses during operation. When these blades experience temperatures beyond their designed operational limits, material integrity can be compromised, leading to stress rupture. The leading edge of a turbine blade is particularly susceptible to these high-temperature effects due to the intense aerodynamic forces and thermal gradients encountered at this crucial point. If a blade is subjected to temperatures that exceed its material capabilities, it can lead to a breakdown in the crystal structure of the metal, resulting in cracks. These stress rupture cracks are typically indicative of thermal fatigue failures rather than other issues such as excessive vibration, improper blade alignment, or manufacturing-related residual stresses. In summary, the presence of stress rupture cracks is a clear sign of over-temperature conditions, underscoring the importance of monitoring operating temperatures to ensure the longevity and safety of turbine blades.