What occurs if the propeller linkage fails?

When the propeller linkage fails, the functioning of the propeller control system is compromised. In this situation, the propeller will generally maintain its last set RPM due to the mechanical design of the system, which does not allow for a sudden change in propeller pitch or RPM. Specifically, a common phenomenon is that the propeller RPM will remain at the last RPM setting or default to a predetermined safety RPM, such as 2000 RPM, which is often engineered into the system as a fail-safe measure. This allows for a stable flight condition, avoiding extremes that could result from erratic or completely disengaged control mechanisms.

The other options do not accurately reflect the nature of the propeller linkage failure. For instance, a drop to idle RPM or an increase to maximum RPM would suggest active control of the pitch changing, which is not feasible when the linkage is malfunctioning. Similarly, erratic fluctuations are unlikely as the system is designed to stabilize at a specific operational parameter in case of failure.