Prior to thrust bearing measurements on the main engine, how long should the turbine be at ambient temperature with throttles shut?

To accurately perform thrust bearing measurements on the main engine, it is essential for the turbine to reach ambient temperature to ensure that the measurements reflect the true operating conditions without thermal expansion affecting the results. Allowing the turbine to sit at ambient temperature for 24 hours with throttles shut provides sufficient time for the engine components to cool down completely. This timeframe helps in stabilizing the thermal characteristics of the system, reducing the potential inaccuracies that may arise from residual heat.

Achieving this cooling period minimizes variables that could compromise the precision of the measurements and ensures that they align with standard procedure practices. The other durations specified do not correspond to the typical industry standards for this specific procedure, making the 24-hour period the correct and practical choice for measurement accuracy.