What does LUSU indicate?

• A. Lock unlock shaft
• B. Loss of reduction gear L/O pressure
• C. Lube oil system leak
• D. Line shaft isolation

Answer: (A)

LUSU is about the status of the propulsion shaft’s locking mechanism. It signals whether the shaft lock is engaged or released, which is crucial for safe maintenance and operations. If the indicator shows the shaft is locked, the shaft is immobilized and safe to work on in that state; if it shows unlocked, the shaft can rotate and requires caution or further action before maintenance or alignment.

This is why the option describing the shaft’s lock/unlock state is the correct one. The other possibilities refer to oil leaks, pressure loss in the reduction gear, or line shaft isolation—issues that would be indicated by different alarms or indicators and are not what LUSU communicates.